Chevy 250 hp confusion

Posted by: TonyPa

Chevy 250 hp confusion - 07/20/17 03:22 PM

Hi guys...I just bought a completely stock 74 Nova off of a older gentleman two months ago.
It has the 250, which I truly love. Th350 tranny and a 8.5 posi, with I believe might have 3:08's. I never verified this. Only going by a nova resource website that said that's what they put in them.
At present I have 100hp, and 175lbs of torque. which makes it tough where I live with climbing hills.
I'm not after big hp, but would like around 170-190. I know I have seen a lot of bolt on options. Not cheap, but available.
I refuse to go V8, I truly like the 6's.
Here's my confusion.
Although I have a low mileage engine that is very quiet and in great condition, and runs perfect.
I came across a 250 out of a 66 impala, that runs great for a 100 bucks. I looked up the specs and online and everywhere it states 155hp with 235 lbs of torque.
I'm confused because the stroke and bore are the same?? I did see that my compression is 8.25.1 and the 66 250 is 8.51.1
So the compression seems a tiny bit higher. Not sure why?
Is that where the extra 55hp is coming in?
I can't bolt on 55hp for a 100 bucks.
But I've also been told that how they changed the hp ratings over the years? Just confused and need advice. What's the true difference? ..,thank you!!
Posted by: efi-diy

Re: Chevy 250 hp confusion - 07/20/17 05:58 PM

Upto 1971 all the HP ratings were gross, no muffler, no fan, no alternator, and sometimes a deep sump dyno oil pan.

After 1972, this changed to net - all the parts that are needed to run a car were required to be added. The drop in compression maybe took out 5 HP. Changing the engine for the 66 - not worth the trouble.

If you tested the 66 engine to net spec's it would be with in 10 hp of whats in the car now.
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/20/17 08:52 PM

Thank you! I could not figure out why the 55hp gain from and older engine, but the same stroke and bore. I appreciate your response.
I guess I will have to figure out which way to go, to get a little more hp.
My engine is very quiet, and solid. I honestly didn't want to not use it.
I see they "someone" out there makes a Holley 390? And maybe and HEI, and some headers. I don't know how much that combo would wake it up.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 12:31 AM

Minor correction on net and gross HP. 1970 and earlier numbers are gross, 1972 and later are net. However both net and gross were advertised in 1971. I have the numbers only for Camaros, and since Nova is it's close cousin there should not be much difference:

1967 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo-3/4spd 3.55perf-all
1968 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo3/4spd 2.56econ-pglide 3.55perf-all
1969 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo3/4spd 2.56econ-pglide&TH350 3.08perf-pglide 3.36perf-3/4spd
1970 -155hp -8.5:1 -non-int -2"ex -points -3.08 3spd 2.73pglide
1971 -145hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide

1971 -110hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide
1972 -110hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide
1973 -100hp -8.25:1 -non-int -2"ex -points -3.08 3spd&TH350
1974 -100hp -8.25:1 -non-int -2"ex -points -3.08 3spd&TH350
1975 -105hp -8.25:1 -1st-int -2.25"ex -HEI -3.08 3spd 2.73TH350 3.08perf-TH350
1976 -105hp -8.25:1 -1st-int -2.25"ex -HEI -2.73 3spd&TH350 3.08perf-both
1977 -110hp -8.3:1 -2nd-int -2.25"ex -HEI -2.73 3spd&TH350 3.08perf-TH350
1978 -110hp -8.1:1 -2nd-int -2.25"ex -HEI -2.73 3spd&TH350
1979 -115hp -8.0:1 -non-int -2.25"ex -HEI -2.56 3spd&TH350

Sorry if the axle ratios are a bit messy on there. Your '74 auto Nova with posi should be 8.25:1 CR with TH350 and a 3.08 posi rear. I'm not sure what year they went to the 8.5" rear, but IntegratedJ's and my '78s are 8.5", so I assume the '75 to '77 must have been as well. The only advantage the '66 engine has over the '74 is 0.25:1 extra CR. Hardly worth it.

Your '74 has hardened exhaust seats for unleaded, which is a plus. And it has a non-integrated cylinder head which is great for upgrading. Your wheezy 210cfm Monojet and 2" exhaust manifold can be swapped for a Holley 390cfm, Offy intake, and a pair of Langdon cast headers. Tubular headers won't fit on car engines, only trucks have the clearance. An alternative is getting a 2.5" HD 292 exhaust manifold or reproduction of it for tractor/generator inlines. HEI was the year after yours, but definitely upgrade to an HEI distributor with a quality cap/rotor/wires. Upgrade it with a Crane adjustable vacuum advance and springs kit. And while you're at it, swap the fixed 4 blade fan for the 3 blade truck clutch fan, or electric fans.

To figure out power upgrade numbers, best consult DueceCoupe and his Gonkulator.

But to take full advantage of the bolt ons, the stock non-integrated head is the weak point. That needs lumps and 1.84"/1.6" valve upgrades, and decking the head to reduce CCs too. And upgrading from the stock cam at least a step up to a hydraulic 240 or more.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/21/17 07:21 AM

It might be worthwhile to pick up that $100 engine. I believe you have the integrated head. The earlier 250's had the intake and exhaust non-integrated. You can swap the head over, get an Offy intake, mild cam, Langdon split headers and gain a lot of power.

The tough thing for you is that none of that is available for your integrated head. Changing the head opens up a lot more possibilities for bolt-ons that will make a huge difference.

Lumps and valves could be done before you do the swap. This way you're just doing a little at a time and keeping the monthly budget low enough to keep the wife happy.

...you could make the old lower end into a coffee table...
Posted by: THE FRENCHTOWN FLYER

Re: Chevy 250 hp confusion - 07/21/17 07:54 AM

Originally Posted By: gbauer

...you could make the old lower end into a coffee table...

Mine get made into wine racks.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/21/17 08:12 AM

Originally Posted By: THE FRENCHTOWN FLYER
Originally Posted By: gbauer

...you could make the old lower end into a coffee table...

Mine get made into wine racks.


Why not both?

https://s-media-cache-ak0.pinimg.com/originals/2d/e4/bc/2de4bc0336e6cdd75f4e73804bc12a78.jpg

With a matching side table?

http://i.ebayimg.com/00/s/MTYwMFg3Njk=/z/Pq8AAOSwXY5ZToME/$_35.JPG?set_id=880000500F

Perhaps some lighting for ambiance?

https://s-media-cache-ak0.pinimg.com/originals/4d/56/27/4d5627a1158e720c9f002a3bdf8f216f.jpg

Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 08:22 AM

Originally Posted By: gbauer
It might be worthwhile to pick up that $100 engine. I believe you have the integrated head. The earlier 250's had the intake and exhaust non-integrated. You can swap the head over, get an Offy intake, mild cam, Langdon split headers and gain a lot of power.

The tough thing for you is that none of that is available for your integrated head. Changing the head opens up a lot more possibilities for bolt-ons that will make a huge difference.

Lumps and valves could be done before you do the swap. This way you're just doing a little at a time and keeping the monthly budget low enough to keep the wife happy.

...you could make the old lower end into a coffee table...


He does NOT have an integrated head. The 1st integrated head is 1975 and 1976. The second version is 1977 and 1978. !979 went back to the non-integrated head for the last year in cars.

The integrated head came with a change to a 2.25" exhaust with a catalytic converter, HEI, and the dual profile camshaft. The only difference between his 1974 engine the 1966 is a slightly less dished piston (0.25 CCs worth). Oh, and the old 1bbl versus the Monojet on his.
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/21/17 08:32 AM

Originally Posted By: Lifeguard
Minor correction on net and gross HP. 1970 and earlier numbers are gross, 1972 and later are net. However both net and gross were advertised in 1971. I have the numbers only for Camaros, and since Nova is it's close cousin there should not be much difference:

1967 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo-3/4spd 3.55perf-all
1968 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo3/4spd 2.56econ-pglide 3.55perf-all
1969 -155hp -8.5:1 -non-int -2"ex -points -3.08 3/4spd 2.73pglide&econo3/4spd 2.56econ-pglide&TH350 3.08perf-pglide 3.36perf-3/4spd
1970 -155hp -8.5:1 -non-int -2"ex -points -3.08 3spd 2.73pglide
1971 -145hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide

1971 -110hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide
1972 -110hp -8.5:1 -non-int -2"ex -points -3.08 3spd&pglide
1973 -100hp -8.25:1 -non-int -2"ex -points -3.08 3spd&TH350
1974 -100hp -8.25:1 -non-int -2"ex -points -3.08 3spd&TH350
1975 -105hp -8.25:1 -1st-int -2.25"ex -HEI -3.08 3spd 2.73TH350 3.08perf-TH350
1976 -105hp -8.25:1 -1st-int -2.25"ex -HEI -2.73 3spd&TH350 3.08perf-both
1977 -110hp -8.3:1 -2nd-int -2.25"ex -HEI -2.73 3spd&TH350 3.08perf-TH350
1978 -110hp -8.1:1 -2nd-int -2.25"ex -HEI -2.73 3spd&TH350
1979 -115hp -8.0:1 -non-int -2.25"ex -HEI -2.56 3spd&TH350

Sorry if the axle ratios are a bit messy on there. Your '74 auto Nova with posi should be 8.25:1 CR with TH350 and a 3.08 posi rear. I'm not sure what year they went to the 8.5" rear, but IntegratedJ's and my '78s are 8.5", so I assume the '75 to '77 must have been as well. The only advantage the '66 engine has over the '74 is 0.25:1 extra CR. Hardly worth it.

Your '74 has hardened exhaust seats for unleaded, which is a plus. And it has a non-integrated cylinder head which is great for upgrading. Your wheezy 210cfm Monojet and 2" exhaust manifold can be swapped for a Holley 390cfm, Offy intake, and a pair of Langdon cast headers. Tubular headers won't fit on car engines, only trucks have the clearance. An alternative is getting a 2.5" HD 292 exhaust manifold or reproduction of it for tractor/generator inlines. HEI was the year after yours, but definitely upgrade to an HEI distributor with a quality cap/rotor/wires. Upgrade it with a Crane adjustable vacuum advance and springs kit. And while you're at it, swap the fixed 4 blade fan for the 3 blade truck clutch fan, or electric fans.

To figure out power upgrade numbers, best consult DueceCoupe and his Gonkulator.

But to take full advantage of the bolt ons, the stock non-integrated head is the weak point. That needs lumps and 1.84"/1.6" valve upgrades, and decking the head to reduce CCs too. And upgrading from the stock cam at least a step up to a hydraulic 240 or more.


Thank you for the extensive answer!!!

Yes mine is a 10 bolt 8.5 rear. I dont like the 308's in the rear, but they'll have to do for now. I am not racing or anything. Just a daily driver but would like some different size gears later on.

I didn't know my 74 had hardened exhaust seats for unleaded, since I didn't have a cat converter. I keep adding lucas ethanol treatment with every tank full.

The combination you just named is pretty much what I wanted to do. I figure start buying the parts, and once I have everything, then do the work.

My head was replaced right before I bought the car. He had blown the rad, and ended up cracking the head. He bought a used head, and had broughers speed shop check the used head he bought, and had it pressure tested also. Car runs perfect, besides me wanting more hp for hills...etc.

I did have the valve cover off to replace the gasket, he over tightened it...., and the numbers I found were as follows:

J69 towards the front of the engine on the head.
Towards the middle, looked like 1828000

I looked everywhere, but someone on a Nova forum said it appeared to be a 292 head from 69? I dunno. I can't find those numbers anywhere on the net.

I don't see those 390 holleys online anywhere, unless I am just being stupid and getting older. I found a local Offy intake on the craiglist, but he wants 500 bucks. Bit steep for me on a used one.
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/21/17 08:34 AM

Originally Posted By: gbauer
It might be worthwhile to pick up that $100 engine. I believe you have the integrated head. The earlier 250's had the intake and exhaust non-integrated. You can swap the head over, get an Offy intake, mild cam, Langdon split headers and gain a lot of power.

The tough thing for you is that none of that is available for your integrated head. Changing the head opens up a lot more possibilities for bolt-ons that will make a huge difference.

Lumps and valves could be done before you do the swap. This way you're just doing a little at a time and keeping the monthly budget low enough to keep the wife happy.

...you could make the old lower end into a coffee table...


Mines not the integrated head. That started in 75. I have a 74, so I just made the cut...LOL
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 09:10 AM

Originally Posted By: TonyPa


Thank you for the extensive answer!!!

Yes mine is a 10 bolt 8.5 rear. I dont like the 308's in the rear, but they'll have to do for now. I am not racing or anything. Just a daily driver but would like some different size gears later on.

I didn't know my 74 had hardened exhaust seats for unleaded, since I didn't have a cat converter. I keep adding lucas ethanol treatment with every tank full.

The combination you just named is pretty much what I wanted to do. I figure start buying the parts, and once I have everything, then do the work.

My head was replaced right before I bought the car. He had blown the rad, and ended up cracking the head. He bought a used head, and had broughers speed shop check the used head he bought, and had it pressure tested also. Car runs perfect, besides me wanting more hp for hills...etc.

I did have the valve cover off to replace the gasket, he over tightened it...., and the numbers I found were as follows:

J69 towards the front of the engine on the head.
Towards the middle, looked like 1828000

I looked everywhere, but someone on a Nova forum said it appeared to be a 292 head from 69? I dunno. I can't find those numbers anywhere on the net.

I don't see those 390 holleys online anywhere, unless I am just being stupid and getting older. I found a local Offy intake on the craiglist, but he wants 500 bucks. Bit steep for me on a used one.



I should make a chart for that, but Photobucket won't let me post pics on the forum anymore. Still hunting for a free pic host that won't do the same in the future.

From 1972 model year on, they induction hardened the exhaust valve seat so they all run on 87 unleaded after that. But since you have a replacement head off a '69 292, you don't have it.

$500 for a used Offy is ridiculous. I'll look up my parts list on my spreadsheet and post it with links to sources in a few hours.

A running 250 for $100 is not a bad price. The wrecking yard up the road from me wanted $300 for a running 250 Varajet head engine out of an '84 truck. A second head is nice for working on while having a running car.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 11:51 AM

Here's another thorough answer. Feel free to shop for the best deals, I just linked to Summit Racing for ease of reference. There might be some alternate parts that are better or cheaper too.

For the HEI, here's my parts list and links assuming you are getting a functional or rebuilt HEI distributor. I recommend the Crane kit because it has the springs and advance you need to do everything. The BWD cap and rotor were higher quality pieces than the stock replacement, and I included the wires and retainer I used (for some reason I can't find the WR1 retainer on Advance Auto anymore). You can probably reuse the coil cover too, and use the stock coil as long as it is good.

Crane Vacuum Advance Kit 99600-1 $35.40 https://www.summitracing.com/parts/crn-99600-1

Fel-Pro distributor base gasket 12665 $0.97 https://www.summitracing.com/parts/fel-12665

BWD HEI distributor cap L6 C198 $34.99 https://shop.advanceautoparts.com/p/bwd-distributor-cap-c198/18200052-P?searchTerm=bwd+c198

BWD coil cap cover C198A $8.19 https://shop.advanceautoparts.com/p/bwd-distributor-cap-cover-c198a/20170298-P?searchTerm=bwd+c198

BWD HEI rotor D157 $13.99 https://shop.advanceautoparts.com/p/bwd-distributor-rotor-d157/18200115-P?searchTerm=bwd+d157

BWD plug wire retainer ring WR1 $3.99 https://www.oreillyauto.com/detail/bwd-3...7/chevrolet/p30

Denso 8mm ignition wire set 671-6020 $39.99 https://shop.advanceautoparts.com/p/dens...=denso+671-6020

Spectre Performance spark plug wire sep 4601 $5.99 https://www.summitracing.com/parts/spe-4601



For the intake and exhaust swap, here's a list of all the major and minor parts you will need to put a 390cfm Holley on an Offy intake mounted with the primaries toward the passenger side. Keep your manifold bolts, but you will need to either use washers with the aftermarket parts, or grind down some of the surfaces to make the factory hold-down pieces seat property.

Offenhauser single quad intake manifold w/ linkage 5416 $309.97 https://www.summitracing.com/parts/ofy-5416

Fel-Pro manifold gasket set MS9786 $9.99 https://www.summitracing.com/parts/fel-ms9786

Holley 4160 390cfm 4bbl carb 0-8007 $488.95 https://www.summitracing.com/parts/hly-0-8007

Holley throttle cable bracket 20-88 $27.25 https://www.summitracing.com/parts/hly-20-88

Holley inline fuel filter 152-523 $13.22 https://www.summitracing.com/parts/hly-162-523

Spectre Performance throttle return spring bracket 4708 $6.99 https://www.summitracing.com/parts/spe-4708

Moroso 0.5 carb spacer 64945 $42.97 https://www.summitracing.com/parts/mor-64945

Moroso carb studs 37961 $14.99 https://www.summitracing.com/parts/mor-37961

Trans-Dapt 3 air filter stud 2174 $1.97 https://www.summitracing.com/parts/trd-2174

Proform 10x2 air cleaner 66802 $19.97 https://www.summitracing.com/parts/pro-66802

Summit valve cover breather SUM-G3418 $3.97 https://www.summitracing.com/parts/sum-g3418

Langdon Stovebolt cast exhaust headers 42-0070 $277 http://www.langdonsstovebolt.com/store/#!/Stovebolt-Cast-Exhaust-Headers-for-GM194-230-250-292-engines/p/1395980/category=18665955

Langdon Heat Plate 10-9999 $30 http://www.langdonsstovebolt.com/store/#!/Heat-Plate-for-GM194-230-250-292-Inlet-Manifold/p/1222036/category=18665977&forcescroll=true

pair of plumbing pipe tees from hardware store, plus additional heater hose to route coolant to heat plate (not sure on size)

two 2.25 to 2 reducer pipes for the Stovebolts (or is it 2.5" to 2", the Langdon website says 2.25"?)

For the exhaust, you can put on a dual 2" exhaust with dual mufflers or glass packs and keep the six cylinder whoop-whoop exhaust note. If you want to settle the exhaust sound down, then add a crossover pipe or run them through a single transverse muffler in the stock location between the axle and fuel tank. An alternative is to run the dual 2" pipes back to a Y-pipe, then a single 2.5" exhaust and muffler from there to the tailpipe.



For vacuum components, you are going to have to delete the EGR valve and replace its tee to it from the vacuum line. You are also removing the EFE valve and vacuum lines, plugging the sensor whole in the engine block, as this system is replaced by the coolant heat from the heater core running to the Langdon plate on the Offy. I am assuming that you are going the cheap route and replacing the ducted THERMAC air cleaner with a simple open element, and eliminating that vacuum line (if not, then you have to find a 4bbl unit along with a bolt on stove pipe and duct route, but probably keeping the factory breather vent filter in the assembly).

You'll want to keep the PCV and EVAP canister so that you don't smell up the garage with fuel vapor. But the fuel bowl vent line valve will need to be capped as the Holley has open fuel bowl vents. The thermal valve on the water neck will only open vacuum to the EVAP during highway cruising conditions; but not during warmup, idle, or under load. If you have power brakes, you'll need a fitting for the Offy manifold to connect that line. Photobucket will not let me imbed pictures in postings anymore, so here's a direct link to my diagram for vacuum layout on the Holley:

http://i1109.photobucket.com/albums/h434/Lifeguard2005/emission-hose-diagram_zpsux6ry15k.png

http://i1109.photobucket.com/albums/h434/Lifeguard2005/Holley_zpsbwxjpkba.png
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 12:19 PM

Almost forgot. An alternative to the Langdon Stovebolt cast headers is a reproduction manifold for the 292:

http://www.ebay.com/itm/Exhaust-Manifold-Made-To-Fit-John-Deere-Combines-w-292-Chevy-Engine/400750523442?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

People have complained that the castings for these parts have some shift and will take a bit of grinding to clean them up, and the Offy intake needs a few extra gaskets between manifolds for the gap. But you don't need the coolant heat for the intake, as the passive exhaust heat will warm the Offy quite well. And of course you can use a single 2.5" exhaust system with it instead.

If you can find a HD Chevy truck with 292, those have the same manifold with EFE flapper valve on them. The HD came with a 250cfm Monojet instead of the 210cfm for SD, and the exhaust manifold had a 2.5" outlet instead of the later stock 2.25" (I think earlier 292s come with 2" manifolds no matter what capacity the truck was). That is a good cheap exhaust alternative, and will use your EFE lines to work the flapper in it for warm up.


To free up some hp, eithe replace the fixed blade fan and spacer with an electric fan(s) or replace with the later L6 truck fan that had 3 blades and a clutch:

http://www.borthautoparts.com/images/cars/chevy/1980%20Chevy%20Pick%20up%20Truck%20350%20Engine/1980-81%20Chevy%20Truck%20Engine%203%20Blade%20Clutch%20Fan%20No.H-14015379%20%20H537%20Blazer,Jimmy,Gmc%20Truck.jpg

You just need to get some shorter bolts to attach it to the water pump and pulley. For a bit less drag, you can also hunt down the truck pulley that came with the fixed fan blade before the clutch one. It is 1" greater diameter, and will be like adding an under drive pulley to the crank (since we can't do that with the L6 as the balancer is also the belt pulley). I'm not sure on the part number for this, so I can't say what years and accessories combos to look for. IntegratedJ has one of these on his Nova. The power steering and alternator belts will need to be slightly longer too.
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/21/17 07:54 PM

Originally Posted By: Lifeguard
Originally Posted By: TonyPa


Thank you for the extensive answer!!!

Yes mine is a 10 bolt 8.5 rear. I dont like the 308's in the rear, but they'll have to do for now. I am not racing or anything. Just a daily driver but would like some different size gears later on.

I didn't know my 74 had hardened exhaust seats for unleaded, since I didn't have a cat converter. I keep adding lucas ethanol treatment with every tank full.

The combination you just named is pretty much what I wanted to do. I figure start buying the parts, and once I have everything, then do the work.

My head was replaced right before I bought the car. He had blown the rad, and ended up cracking the head. He bought a used head, and had broughers speed shop check the used head he bought, and had it pressure tested also. Car runs perfect, besides me wanting more hp for hills...etc.

I did have the valve cover off to replace the gasket, he over tightened it...., and the numbers I found were as follows:

J69 towards the front of the engine on the head.
Towards the middle, looked like 1828000

I looked everywhere, but someone on a Nova forum said it appeared to be a 292 head from 69? I dunno. I can't find those numbers anywhere on the net.

I don't see those 390 holleys online anywhere, unless I am just being stupid and getting older. I found a local Offy intake on the craiglist, but he wants 500 bucks. Bit steep for me on a used one.



I should make a chart for that, but Photobucket won't let me post pics on the forum anymore. Still hunting for a free pic host that won't do the same in the future.

From 1972 model year on, they induction hardened the exhaust valve seat so they all run on 87 unleaded after that. But since you have a replacement head off a '69 292, you don't have it.

$500 for a used Offy is ridiculous. I'll look up my parts list on my spreadsheet and post it with links to sources in a few hours.

A running 250 for $100 is not a bad price. The wrecking yard up the road from me wanted $300 for a running 250 Varajet head engine out of an '84 truck. A second head is nice for working on while having a running car.


I used photobucket for years, but it got flakey now. I am going to start using http://imgur.com/.

I never verified if my head is a 292, only went by what someone told me on the number I posted above. I can't find the numbers anywhere.

I thought 500 was way out of control! SO I never even bothered to call and barter with him, not being that high already.

See, thats my thought.. For a 100 bucks, put it on a stand, and pull the head, and mess with the head. And save the bottom end since mine is still in good condition. Or...I guess take my time, and redo the one on the stand completely? I hate making decisions..LOL
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/21/17 08:01 PM

Originally Posted By: Lifeguard
Here's another thorough answer. Feel free to shop for the best deals, I just linked to Summit Racing for ease of reference. There might be some alternate parts that are better or cheaper too.

For the HEI, here's my parts list and links assuming you are getting a functional or rebuilt HEI distributor. I recommend the Crane kit because it has the springs and advance you need to do everything. The BWD cap and rotor were higher quality pieces than the stock replacement, and I included the wires and retainer I used (for some reason I can't find the WR1 retainer on Advance Auto anymore). You can probably reuse the coil cover too, and use the stock coil as long as it is good.

Crane Vacuum Advance Kit 99600-1 $35.40 https://www.summitracing.com/parts/crn-99600-1

Fel-Pro distributor base gasket 12665 $0.97 https://www.summitracing.com/parts/fel-12665

BWD HEI distributor cap L6 C198 $34.99 https://shop.advanceautoparts.com/p/bwd-distributor-cap-c198/18200052-P?searchTerm=bwd+c198

BWD coil cap cover C198A $8.19 https://shop.advanceautoparts.com/p/bwd-distributor-cap-cover-c198a/20170298-P?searchTerm=bwd+c198

BWD HEI rotor D157 $13.99 https://shop.advanceautoparts.com/p/bwd-distributor-rotor-d157/18200115-P?searchTerm=bwd+d157

BWD plug wire retainer ring WR1 $3.99 https://www.oreillyauto.com/detail/bwd-3...7/chevrolet/p30

Denso 8mm ignition wire set 671-6020 $39.99 https://shop.advanceautoparts.com/p/dens...=denso+671-6020

Spectre Performance spark plug wire sep 4601 $5.99 https://www.summitracing.com/parts/spe-4601



For the intake and exhaust swap, here's a list of all the major and minor parts you will need to put a 390cfm Holley on an Offy intake mounted with the primaries toward the passenger side. Keep your manifold bolts, but you will need to either use washers with the aftermarket parts, or grind down some of the surfaces to make the factory hold-down pieces seat property.

Offenhauser single quad intake manifold w/ linkage 5416 $309.97 https://www.summitracing.com/parts/ofy-5416

Fel-Pro manifold gasket set MS9786 $9.99 https://www.summitracing.com/parts/fel-ms9786

Holley 4160 390cfm 4bbl carb 0-8007 $488.95 https://www.summitracing.com/parts/hly-0-8007

Holley throttle cable bracket 20-88 $27.25 https://www.summitracing.com/parts/hly-20-88

Holley inline fuel filter 152-523 $13.22 https://www.summitracing.com/parts/hly-162-523

Spectre Performance throttle return spring bracket 4708 $6.99 https://www.summitracing.com/parts/spe-4708

Moroso 0.5 carb spacer 64945 $42.97 https://www.summitracing.com/parts/mor-64945

Moroso carb studs 37961 $14.99 https://www.summitracing.com/parts/mor-37961

Trans-Dapt 3 air filter stud 2174 $1.97 https://www.summitracing.com/parts/trd-2174

Proform 10x2 air cleaner 66802 $19.97 https://www.summitracing.com/parts/pro-66802

Summit valve cover breather SUM-G3418 $3.97 https://www.summitracing.com/parts/sum-g3418

Langdon Stovebolt cast exhaust headers 42-0070 $277 http://www.langdonsstovebolt.com/store/#!/Stovebolt-Cast-Exhaust-Headers-for-GM194-230-250-292-engines/p/1395980/category=18665955

Langdon Heat Plate 10-9999 $30 http://www.langdonsstovebolt.com/store/#!/Heat-Plate-for-GM194-230-250-292-Inlet-Manifold/p/1222036/category=18665977&forcescroll=true

pair of plumbing pipe tees from hardware store, plus additional heater hose to route coolant to heat plate (not sure on size)

two 2.25 to 2 reducer pipes for the Stovebolts (or is it 2.5" to 2", the Langdon website says 2.25"?)

For the exhaust, you can put on a dual 2" exhaust with dual mufflers or glass packs and keep the six cylinder whoop-whoop exhaust note. If you want to settle the exhaust sound down, then add a crossover pipe or run them through a single transverse muffler in the stock location between the axle and fuel tank. An alternative is to run the dual 2" pipes back to a Y-pipe, then a single 2.5" exhaust and muffler from there to the tailpipe.



For vacuum components, you are going to have to delete the EGR valve and replace its tee to it from the vacuum line. You are also removing the EFE valve and vacuum lines, plugging the sensor whole in the engine block, as this system is replaced by the coolant heat from the heater core running to the Langdon plate on the Offy. I am assuming that you are going the cheap route and replacing the ducted THERMAC air cleaner with a simple open element, and eliminating that vacuum line (if not, then you have to find a 4bbl unit along with a bolt on stove pipe and duct route, but probably keeping the factory breather vent filter in the assembly).

You'll want to keep the PCV and EVAP canister so that you don't smell up the garage with fuel vapor. But the fuel bowl vent line valve will need to be capped as the Holley has open fuel bowl vents. The thermal valve on the water neck will only open vacuum to the EVAP during highway cruising conditions; but not during warmup, idle, or under load. If you have power brakes, you'll need a fitting for the Offy manifold to connect that line. Photobucket will not let me imbed pictures in postings anymore, so here's a direct link to my diagram for vacuum layout on the Holley:

http://i1109.photobucket.com/albums/h434/Lifeguard2005/emission-hose-diagram_zpsux6ry15k.png

http://i1109.photobucket.com/albums/h434/Lifeguard2005/Holley_zpsbwxjpkba.png


WOW!!! Thank you!! Thats what I call being very helpful!

I had no idea those langdon split manifolds were so cheap. Under 300 bucks!! I also had no idea they still sold the Offy intake, and Holley for our adaption process! This is all good news. I can buy a part at a time!

Your information is absolutely appreciated. I feel really at home not like an outsider wanting to keep my 6 in my car! I would truly be happy picking up about 50-75 hp. Looks like that may be possible.
Posted by: TonyPa

Re: Chevy 250 hp confusion - 07/21/17 08:05 PM

Originally Posted By: Lifeguard
Almost forgot. An alternative to the Langdon Stovebolt cast headers is a reproduction manifold for the 292:

http://www.ebay.com/itm/Exhaust-Manifold-Made-To-Fit-John-Deere-Combines-w-292-Chevy-Engine/400750523442?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

People have complained that the castings for these parts have some shift and will take a bit of grinding to clean them up, and the Offy intake needs a few extra gaskets between manifolds for the gap. But you don't need the coolant heat for the intake, as the passive exhaust heat will warm the Offy quite well. And of course you can use a single 2.5" exhaust system with it instead.

If you can find a HD Chevy truck with 292, those have the same manifold with EFE flapper valve on them. The HD came with a 250cfm Monojet instead of the 210cfm for SD, and the exhaust manifold had a 2.5" outlet instead of the later stock 2.25" (I think earlier 292s come with 2" manifolds no matter what capacity the truck was). That is a good cheap exhaust alternative, and will use your EFE lines to work the flapper in it for warm up.


To free up some hp, eithe replace the fixed blade fan and spacer with an electric fan(s) or replace with the later L6 truck fan that had 3 blades and a clutch:

http://www.borthautoparts.com/images/cars/chevy/1980%20Chevy%20Pick%20up%20Truck%20350%20Engine/1980-81%20Chevy%20Truck%20Engine%203%20Blade%20Clutch%20Fan%20No.H-14015379%20%20H537%20Blazer,Jimmy,Gmc%20Truck.jpg

You just need to get some shorter bolts to attach it to the water pump and pulley. For a bit less drag, you can also hunt down the truck pulley that came with the fixed fan blade before the clutch one. It is 1" greater diameter, and will be like adding an under drive pulley to the crank (since we can't do that with the L6 as the balancer is also the belt pulley). I'm not sure on the part number for this, so I can't say what years and accessories combos to look for. IntegratedJ has one of these on his Nova. The power steering and alternator belts will need to be slightly longer too.


I truly wanted dual exhaust, with quiet mufflers though. Nothing too noisy. So the offy intake, and langdon splits will work together?

I didn't know if there was any gain from using a 292 manifold. I did read someone else did that.

Electric fan would be nice honestly. I never hooked one up from scratch. But can't be that hard.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/21/17 09:04 PM

Originally Posted By: TonyPa


I truly wanted dual exhaust, with quiet mufflers though. Nothing too noisy. So the offy intake, and langdon splits will work together?

I didn't know if there was any gain from using a 292 manifold. I did read someone else did that.

Electric fan would be nice honestly. I never hooked one up from scratch. But can't be that hard.


You're welcome. I'm in the same situation. I bought a non-running '78 Camaro with an inline, 3spd manual, and an open 2.73 rear. Original intent was to swap a V8 and 4spd or TH350, but I played with the engine a bit and got it running. I got a lot of attention for the six from bystanders and online, plus I went through a financial hardship, so I decided to investigate keeping it that way and working on it.

Yeah, not as cheap as headers, carb and intake for a small block but still around a grand for the main stuff. Yeah, the Langdon Stovebolts will work with Offy when you use the heat plate hooked into the coolant to warm the intake.

I was missing everything from the cat on back, so I swapped it out for the '77-'81 Z28 cat back dual resonator setup. Quieted it down for the condo association. IntegratedJ is putting together a dual 2" that Ys into a 2.5" down through a single transverse muffler on his '78 Nova with auto.

Your exhaust manifold is a single 2" outlet. The later 292 manifold came in two versions, the SD with 2.25" outlet and the HD version with a 2.5" outlet. For a daily driver or mannered street cruiser with a smaller cam, a dual 2" setup or a single 2.5" exhaust is the right size.

I have my electric fans out right now, and I'm using the 3 blade clutch fan. But when I flush my cooling system and replace the thermostat next, I'm going to put them back on and run a wire from a connector at the electric choke to the relay so that the fans will stop running when I turn the engine off.

The cylinder head is a big part of upgrading the inline. There's a lot of machine work involved to add lumps, bigger valves, multi angle valve job, and deck the head to reduce CCs. The cylinder head is about $800 to $1200 depending on how much of the work you do yourself and how cheap your machine shop is.

Sounds like you want to do little by little as you can afford it. Probably start with HEI first as that's your cheapest upgrade, or adding electric fans. Then you have a choice between doing the exhaust or intake next. Probably head and camshaft last. Beyond that, you can try to raise compression with pistons, but unless you can find some old 307 factory flat tops or TRW forged flat tops, the only option is the Ross pistons which are pricey. Oh, and sounds like you want to swap out the 3.08 posi gears for some 3.42 at some point.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/24/17 08:42 PM

I was looking at my notes on timing. Looks like I was planning on setting 10*@800rpm initial, with 20-22* centrifugal with the springs all in around 3000rpm. Then setting 12* vacuum advance without the EGR (16* if were with the EGR). And I expanded the spark plug gap from 0.035" to 0.045". I also bought a variety of plugs so that I could swap to index them to point toward the exhaust valve.

I just got my Monojet in for now, so I can't do much with that. Just set the idle for my manual transmission at 800rpm, base idle at 425rpm (screw setting, with solenoid unplugged), fast idle arm at 2000rpm, and set the idle screw starting at two turns from full seat to back it off until rpm does not increase.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/25/17 08:15 AM

Originally Posted By: Lifeguard
Originally Posted By: gbauer
It might be worthwhile to pick up that $100 engine. I believe you have the integrated head. The earlier 250's had the intake and exhaust non-integrated. You can swap the head over, get an Offy intake, mild cam, Langdon split headers and gain a lot of power.

The tough thing for you is that none of that is available for your integrated head. Changing the head opens up a lot more possibilities for bolt-ons that will make a huge difference.

Lumps and valves could be done before you do the swap. This way you're just doing a little at a time and keeping the monthly budget low enough to keep the wife happy.

...you could make the old lower end into a coffee table...


He does NOT have an integrated head. The 1st integrated head is 1975 and 1976. The second version is 1977 and 1978. !979 went back to the non-integrated head for the last year in cars.

The integrated head came with a change to a 2.25" exhaust with a catalytic converter, HEI, and the dual profile camshaft. The only difference between his 1974 engine the 1966 is a slightly less dished piston (0.25 CCs worth). Oh, and the old 1bbl versus the Monojet on his.


Thanks. I was a year off.

In that case just do bolt-ons a little at a time like I did.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/25/17 08:16 AM

Originally Posted By: Lifeguard

Still hunting for a free pic host that won't do the same in the future.


try www.imgur.com

I use it all the time. Free and easy to use.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/25/17 09:06 AM

Couple of things I learned the hard way:

Buy a new carb. Don't bother with rebuilding an old one. You'll end up at the same price point in the end.

HEI: I went with an ebay EFI distributor. It lasted 2 years before going bad but it was cheap so I just bought the same one again. Also be sure to remove the resistance wire from the firewall to the distributor.

Do it in stages. I started with Langdon headers and made my own heat plate. Just get the Langdon heat plate. You won't save money making it yourself. Sealing it is a PITA. I used a ton of RTV.

As far as staging goes here's the order I'd do it in if I did it again:

1) HEI and electric fan. Runs so much smoother that way and frees up a couple ponies. I used a pusher style fan and bought a 3 core radiator on Ebay. came out nice.

2) Offy intake and carb. Use the exhaust heat for now.

3) Langdon split header and exhaust. Heat the carb with water. A couple ways to do it. I tapped into the heater hoses at the fire wall. Others tap into the front of the engine. If you have a tapped hole on your thermostat neck that'll make life easier.

4) Cam. On my Camaro I was able to change the cam by pulling off my grill, unbolting the engine mounts, and jacking up the engine. This gave me just enough room to pull it out the front. You'll also need an aluminum cam gear when you do it and new valve springs. Lifters as well.

5) Head. This is where that spare engine might come into play. Get lump ports and oversized valves.

6) Transmission. I had a powerglide. Swapped to a 2004r. HUGE difference. I highly recommend this one. You can get them used pretty cheaply, wire in the lockout, new linkage, and gear selector bezel. Worth every penny!

7) Gearing. Once you have all that done you can now get better gears.



You can see the heater lines at the firewall. I used brass T's as I couldn't get the plastic ones to hold up.



The linkage for the throttle on the 2004r. Bought a kit somewhere for it. Been a while so I can't recall where. It's critical this is done correctly or you'll burn up the trans. I did it with the trans pan off and a caliper. The other option is with a pressure gauge.



Stovebolt Headers (Langdon). You can have him ceramic coat or buy a can of it at your parts store and do it yourself.



Original cam gear. See that hole with the screw behind it? That's the retainer. I got extremely lucky with mine. When I pulled the cover the engine happened to have been stopped at the perfect spot.



New cam gear. Nice and shiny. Original is a composite and you'll never get it off without breaking it. New one is press-fitted on.

....and for the most important advice I can give you!



USE THE RIGHT OIL! Modern oils do NOT have the right chemical make up for solid lifter engines. Brad Penn makes a good oil for your car. There are others out there as well.

I did my research and on paper Mobil1 appears to have the right stuff. It does NOT. Wiped a cam.

Find a local machine shop or speed shop. They'll sell you the right oil. Don't go to NAPA or other big chain parts stores. In a pinch you can use Valvoline VR1 but I prefer the good stuff.

I live in Hanover, PA now. Somewhat local to you. If you get stuck sometime reach out to me. I love working on these old engines and have enough experience to not do things like I did again...
Posted by: efi-diy

Re: Chevy 250 hp confusion - 07/25/17 06:02 PM

gbauer.. how much do you have into all your modes?
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 07/26/17 07:22 PM

Originally Posted By: gbauer
Couple of things I learned the hard way:

Buy a new carb. Don't bother with rebuilding an old one. You'll end up at the same price point in the end.

HEI: I went with an ebay EFI distributor. It lasted 2 years before going bad but it was cheap so I just bought the same one again. Also be sure to remove the resistance wire from the firewall to the distributor.

Do it in stages. I started with Langdon headers and made my own heat plate. Just get the Langdon heat plate. You won't save money making it yourself. Sealing it is a PITA. I used a ton of RTV.

As far as staging goes here's the order I'd do it in if I did it again:

1) HEI and electric fan. Runs so much smoother that way and frees up a couple ponies. I used a pusher style fan and bought a 3 core radiator on Ebay. came out nice.

2) Offy intake and carb. Use the exhaust heat for now.

3) Langdon split header and exhaust. Heat the carb with water. A couple ways to do it. I tapped into the heater hoses at the fire wall. Others tap into the front of the engine. If you have a tapped hole on your thermostat neck that'll make life easier.

4) Cam. On my Camaro I was able to change the cam by pulling off my grill, unbolting the engine mounts, and jacking up the engine. This gave me just enough room to pull it out the front. You'll also need an aluminum cam gear when you do it and new valve springs. Lifters as well.

5) Head. This is where that spare engine might come into play. Get lump ports and oversized valves.

6) Transmission. I had a powerglide. Swapped to a 2004r. HUGE difference. I highly recommend this one. You can get them used pretty cheaply, wire in the lockout, new linkage, and gear selector bezel. Worth every penny!

7) Gearing. Once you have all that done you can now get better gears.



I guess those of us with 1975 to 1978 cars with integrated heads have to combine steps 2, 3, and 5 into one step. Although that's a good time to do 4 as well. Not sure on which year the Varajet integrated head came into use on trucks.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/27/17 05:45 AM

Originally Posted By: efi-diy
gbauer.. how much do you have into all your modes?


Didn't keep track but I'd say around 4 grand. Keep in mind this was spread out over 3 years and I did most of the work myself. I also never did a job that took more than 2 weekends. I was able to drive it almost every day I owned it (if I wanted to).

She ran really well when I was done. Unfortunately I sold her about 4 months ago to buy a much bigger house on much more land for my kids.

Well worth the heart ache of seeing her drive away one last time...

https://www.youtube.com/watch?v=lJdZDW0AiO8

That was the last I saw her.

On a brighter note the red car is my daily driver. It's every bit as fun and a heck of a lot faster.

I'm thinking my next project car will be a slightly different inline 6.



Used to own one as a daily driver. Sold it when I had my first kid. Really regret that sale...

Mine was a 98 M Roadster with an M50 manifold, cold air intake, Dinan tune, Randy Forbes subframe with dual ear diff, gears, and other stuff. Tore up many an autocross course with it. 275 hp or so. Ran a 13.2 in the 1/4 mile but it wasn't built for straight line racing. It was built for autocross.
Posted by: gbauer

Re: Chevy 250 hp confusion - 07/27/17 05:48 AM

Originally Posted By: Lifeguard

I guess those of us with 1975 to 1978 cars with integrated heads have to combine steps 2, 3, and 5 into one step. Although that's a good time to do 4 as well. Not sure on which year the Varajet integrated head came into use on trucks.


Unless you go forced induction that list is pretty much the only path to take to get decent power out of these. I suppose you could go really radical and get that head that brings the intake on the passenger side and exhaust out the driver's side but I can't see you gaining a whole lot with it.

After all that I did I was still a 15 second car. But it was a very neat 15 seconds and sounded great while doing it.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 07:37 AM

Originally Posted By: Lifeguard
Originally Posted By: TonyPa


I truly wanted dual exhaust, with quiet mufflers though. Nothing too noisy. So the offy intake, and langdon splits will work together?

I didn't know if there was any gain from using a 292 manifold. I did read someone else did that.

Electric fan would be nice honestly. I never hooked one up from scratch. But can't be that hard.


You're welcome. I'm in the same situation. I bought a non-running '78 Camaro with an inline, 3spd manual, and an open 2.73 rear. Original intent was to swap a V8 and 4spd or TH350, but I played with the engine a bit and got it running. I got a lot of attention for the six from bystanders and online, plus I went through a financial hardship, so I decided to investigate keeping it that way and working on it.

Yeah, not as cheap as headers, carb and intake for a small block but still around a grand for the main stuff. Yeah, the Langdon Stovebolts will work with Offy when you use the heat plate hooked into the coolant to warm the intake.

I was missing everything from the cat on back, so I swapped it out for the '77-'81 Z28 cat back dual resonator setup. Quieted it down for the condo association. IntegratedJ is putting together a dual 2" that Ys into a 2.5" down through a single transverse muffler on his '78 Nova with auto.

Your exhaust manifold is a single 2" outlet. The later 292 manifold came in two versions, the SD with 2.25" outlet and the HD version with a 2.5" outlet. For a daily driver or mannered street cruiser with a smaller cam, a dual 2" setup or a single 2.5" exhaust is the right size.

I have my electric fans out right now, and I'm using the 3 blade clutch fan. But when I flush my cooling system and replace the thermostat next, I'm going to put them back on and run a wire from a connector at the electric choke to the relay so that the fans will stop running when I turn the engine off.

The cylinder head is a big part of upgrading the inline. There's a lot of machine work involved to add lumps, bigger valves, multi angle valve job, and deck the head to reduce CCs. The cylinder head is about $800 to $1200 depending on how much of the work you do yourself and how cheap your machine shop is.

Sounds like you want to do little by little as you can afford it. Probably start with HEI first as that's your cheapest upgrade, or adding electric fans. Then you have a choice between doing the exhaust or intake next. Probably head and camshaft last. Beyond that, you can try to raise compression with pistons, but unless you can find some old 307 factory flat tops or TRW forged flat tops, the only option is the Ross pistons which are pricey. Oh, and sounds like you want to swap out the 3.08 posi gears for some 3.42 at some point.


Yeah that's the problem is money of course. I guess it all takes time though. I do see that the head is truly a big improvement for power. I pulled my valvecover to replace the gasket and put the numbers up on the Nova forum since I could not find anything even close to my number.
Seems when he replaced the head according to a fellow that found my numbers online somewhere, he thought my head might be a 1969 292 head. Which I guess is no increase on anything. I can put my nnumbers up. I never found rhrm online.

I do know my gears are holding me back. Truly great on the highway. But i don't do much highway driving. I seen summit sells posi gear packs if thats what their called. About 500 bucks or so. Never installed a complete set up.

I seen you have to really dial them in or something. Many have seemed to change their gears before doing anything and noticed an improvement from that until getting the motor reworked.

Going to a 3.43, is there a pretty good difference from the 3.08? Or is 3.73 better? Or too much for a TH350 3 speed at 45mph cruise?

The parts are pricey and will take time. But would be nice to grab about another 50hp.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 07:46 AM

Originally Posted By: Lifeguard
I was looking at my notes on timing. Looks like I was planning on setting 10*@800rpm initial, with 20-22* centrifugal with the springs all in around 3000rpm. Then setting 12* vacuum advance without the EGR (16* if were with the EGR). And I expanded the spark plug gap from 0.035" to 0.045". I also bought a variety of plugs so that I could swap to index them to point toward the exhaust valve.

I just got my Monojet in for now, so I can't do much with that. Just set the idle for my manual transmission at 800rpm, base idle at 425rpm (screw setting, with solenoid unplugged), fast idle arm at 2000rpm, and set the idle screw starting at two turns from full seat to back it off until rpm does not increase.


Mines set right now at 10 degrees. I didnt want to go any higher. Wasnt sure if it can cause any bad things to happen. It was set at 12 degrees when I got it.

I disconnected my EGR then hooked it back up. I read somewhere that it wont burn the un used fuel or something. I swear with the EGR not connected it felt more snappy. Could have been a placebo with me.

I dont understand how to set the vac advance differently. As in where to set it.

There were new plugs installed on my 74 250 when I boight it. Not sure where the gap is. Should I set mine to .045?

My solenoid isnt working. Has power to it, but when i unplug it, it does nothing. I just found out on here yesterday about the screw in the end. I have to look, I didnt know there was one inside there. I just turned the whole thing. Dont know if mine not working will help with adjusting the screw?
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 07:47 AM

Originally Posted By: gbauer
Originally Posted By: Lifeguard

Still hunting for a free pic host that won't do the same in the future.


try www.imgur.com

I use it all the time. Free and easy to use.


I juat started using it lastnight. Much nicer than photobucket.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 07:57 AM

Originally Posted By: gbauer
Couple of things I learned the hard way:

Buy a new carb. Don't bother with rebuilding an old one. You'll end up at the same price point in the end.

HEI: I went with an ebay EFI distributor. It lasted 2 years before going bad but it was cheap so I just bought the same one again. Also be sure to remove the resistance wire from the firewall to the distributor.

Do it in stages. I started with Langdon headers and made my own heat plate. Just get the Langdon heat plate. You won't save money making it yourself. Sealing it is a PITA. I used a ton of RTV.

As far as staging goes here's the order I'd do it in if I did it again:

1) HEI and electric fan. Runs so much smoother that way and frees up a couple ponies. I used a pusher style fan and bought a 3 core radiator on Ebay. came out nice.

2) Offy intake and carb. Use the exhaust heat for now.

3) Langdon split header and exhaust. Heat the carb with water. A couple ways to do it. I tapped into the heater hoses at the fire wall. Others tap into the front of the engine. If you have a tapped hole on your thermostat neck that'll make life easier.

4) Cam. On my Camaro I was able to change the cam by pulling off my grill, unbolting the engine mounts, and jacking up the engine. This gave me just enough room to pull it out the front. You'll also need an aluminum cam gear when you do it and new valve springs. Lifters as well.

5) Head. This is where that spare engine might come into play. Get lump ports and oversized valves.

6) Transmission. I had a powerglide. Swapped to a 2004r. HUGE difference. I highly recommend this one. You can get them used pretty cheaply, wire in the lockout, new linkage, and gear selector bezel. Worth every penny!

7) Gearing. Once you have all that done you can now get better gears.



You can see the heater lines at the firewall. I used brass T's as I couldn't get the plastic ones to hold up.



The linkage for the throttle on the 2004r. Bought a kit somewhere for it. Been a while so I can't recall where. It's critical this is done correctly or you'll burn up the trans. I did it with the trans pan off and a caliper. The other option is with a pressure gauge.



Stovebolt Headers (Langdon). You can have him ceramic coat or buy a can of it at your parts store and do it yourself.



Original cam gear. See that hole with the screw behind it? That's the retainer. I got extremely lucky with mine. When I pulled the cover the engine happened to have been stopped at the perfect spot.



New cam gear. Nice and shiny. Original is a composite and you'll never get it off without breaking it. New one is press-fitted on.

....and for the most important advice I can give you!



USE THE RIGHT OIL! Modern oils do NOT have the right chemical make up for solid lifter engines. Brad Penn makes a good oil for your car. There are others out there as well.

I did my research and on paper Mobil1 appears to have the right stuff. It does NOT. Wiped a cam.

Find a local machine shop or speed shop. They'll sell you the right oil. Don't go to NAPA or other big chain parts stores. In a pinch you can use Valvoline VR1 but I prefer the good stuff.

I live in Hanover, PA now. Somewhat local to you. If you get stuck sometime reach out to me. I love working on these old engines and have enough experience to not do things like I did again...


That looks nice!! I did find a rebuilt carb on summit for now. Some say not to buy a rebuilt that their junk. Because they dont do the throttle body shaft bushings. But it had a great review by someone. I just need it as a get me by for now.

I do want an HEI I know it should smooth things out a bit. Their all over the internet. Just which one to choose.

You did everything in a nice order. I guess its going to take some time. I need to slow my brain down. My wallet can't keep up...lol

I used regular Castrol. But I added ZDDP additive from rislone. There is a place about a half hour from me that sells Brad Penn.

Im not getting email notifications when theres a post on my threads...ugh
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 08:06 AM

Lovely!!! I joined this forum quite a while back but didnt keep my car long. I made a new username as Tracker64. Didnt realize that my browser somehow grabbed the old one. So I posted as Tonypa and also Tracker64. I hate getting older with technology. Ugh!!!
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/03/17 08:08 AM

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Posted by: TonyPa

Re: Chevy 250 hp confusion - 08/03/17 11:43 AM

No I never heard of it. I'm actually in Irwin, I just put Greensburg because it's the closest big town that people are familiar with. Every time I say Irwin, no one has heard of it. I have to google your area.

Says 3 hours15 minutes from me.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/04/17 12:51 AM

Originally Posted By: Tracker64
Lovely!!! I joined this forum quite a while back but didnt keep my car long. I made a new username as Tracker64. Didnt realize that my browser somehow grabbed the old one. So I posted as Tonypa and also Tracker64. I hate getting older with technology. Ugh!!!


Wait, I'm terribly confused. So you have two accounts here? TonyPA and Tracker64?

The tuneup decal says 0.035" spark plug gap for L6, and 0.045" for V8 small block. Not sure why there is a difference as the HEI is the same save for the shaft length and number of terminals on the cap. And old power and fuel economy trick is to increase plug gap to make a longer spark for igniting the fuel/air mixture. 0.045" is supposed to be the largest gap the stock HEI can handle, so that's what I set mine at. Also bought several different plugs so that I could try them on each cylinder and see which ones face the exhaust valve when seated. I put a line on the porcelain in the direction of the gap so i could see where it indexed at. Plugs #1 and #2 have the intake valves between them, same with #3/4 and #5/6.

My factory specs say 6* @ 800rpm for my 3spd manual, but I advanced it to 10*. I may check it again to see if I can advance it a little more for optimum, after I'm done changing fluids. Plugging my vacuum advance with my vacuum gauge and seeing, and with my timing light seeing where I have peak vacuum. I might stay with 10* or might go up a bit.

Yeah, to set initial idle speed, plug your vacuum advance (instructions say to plug the EGR/EVAP line too) and turn the solenoid on the Monojet with a 9/16" wrench. Then to set the base idle speed, use your 9/16" wrench to hold the solenoid still while you turn the hex screw inside with a 1/8" Allen wrench. Tighten the screw all the way down, then unplug the solenoid. While holding the solenoid with the 9/16" wrench, back out the hex screw until you get the base idle speed you want. Plug the solenoid back in and check to see that your initial idle speed returns.

While you got your vac adv off, have your vacuum gauge hooked and you can adjust the idle mixture screw while you are at it. Start with it at two turns from full seat, and turn it 1/4 turn at a time and watch for peak vacuum. When you see vacuum drop off, back it off a little. I get 20" HG with the mixture screw nearly out. I'm at 820' above sea level here.

The fast idle is set by bending the linkage when it is sitting on the lobe of the cam on the read of the carb. Mine was pretty close. One of these days I'm going to make a video on how to tune all the stock components for reference for YouTube.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/04/17 07:04 AM

Originally Posted By: Lifeguard
Originally Posted By: Tracker64
Lovely!!! I joined this forum quite a while back but didnt keep my car long. I made a new username as Tracker64. Didnt realize that my browser somehow grabbed the old one. So I posted as Tonypa and also Tracker64. I hate getting older with technology. Ugh!!!


Wait, I'm terribly confused. So you have two accounts here? TonyPA and Tracker64?

Here's what happened. About three years ago, if you look at my "TonyPa" profile. I was posting a few times, but ended up selling my car. Well, fast forward three years until now, I could not remember my name and password. So on my "phone", I created a new account under "Tracker64". I have been posting from my phone and tablet. I got on my laptop the other night which I rarely do, mostly when I need a bigger screen to enjoy. My google browser must have held the TonyPa user after all that time. I was posting then scrolled back, and was like...what the heck? I will continue to use Tracker64. I fixed it on my laptop, so TonyPa no longer is saved. Quite humiliating!


The tuneup decal says 0.035" spark plug gap for L6, and 0.045" for V8 small block. Not sure why there is a difference as the HEI is the same save for the shaft length and number of terminals on the cap. And old power and fuel economy trick is to increase plug gap to make a longer spark for igniting the fuel/air mixture. 0.045" is supposed to be the largest gap the stock HEI can handle, so that's what I set mine at. Also bought several different plugs so that I could try them on each cylinder and see which ones face the exhaust valve when seated. I put a line on the porcelain in the direction of the gap so i could see where it indexed at. Plugs #1 and #2 have the intake valves between them, same with #3/4 and #5/6.

I am going to set mine at .045 tomorrow and see what it does. I don't have an HEI yet, but it can't hurt to test it. The plugs are easy to get to. LOL

My factory specs say 6* @ 800rpm for my 3spd manual, but I advanced it to 10*. I may check it again to see if I can advance it a little more for optimum, after I'm done changing fluids. Plugging my vacuum advance with my vacuum gauge and seeing, and with my timing light seeing where I have peak vacuum. I might stay with 10* or might go up a bit.

Mine calls for 8 degrees at 600 rpm. When I got the car they had it set to 12 degrees, not sure why. I backed it to 8, then back up to 10. I wasn't sure if advancing could cause running hot, or dieseling??
I might put it back at 12, and see what happens.


Yeah, to set initial idle speed, plug your vacuum advance (instructions say to plug the EGR/EVAP line too) and turn the solenoid on the Monojet with a 9/16" wrench. Then to set the base idle speed, use your 9/16" wrench to hold the solenoid still while you turn the hex screw inside with a 1/8" Allen wrench. Tighten the screw all the way down, then unplug the solenoid. While holding the solenoid with the 9/16" wrench, back out the hex screw until you get the base idle speed you want. Plug the solenoid back in and check to see that your initial idle speed returns.

I will do that for sure. my solenoid is not working. Power to it, but doesn't function. I will make that adjustment. My buddy told me to unplug my EGR and leave it capped off at the thermostat housing. Dunno why he said to do that. I see that it helps burn up the fuel or something. But he said makes it a bit more snappy. I did it, and I could tell a slight difference, Placebo? Maybe! But I plugged it back in.


While you got your vac adv off, have your vacuum gauge hooked and you can adjust the idle mixture screw while you are at it. Start with it at two turns from full seat, and turn it 1/4 turn at a time and watch for peak vacuum. When you see vacuum drop off, back it off a little. I get 20" HG with the mixture screw nearly out. I'm at 820' above sea level here.

When you say the vac advance unplugged, do you mean put a vac gauge on the carb at that port? I think that port on mine only sucks under throttle pressure, pretty sure anyhow. I don't have a vac gauge!! Ugh!!


The fast idle is set by bending the linkage when it is sitting on the lobe of the cam on the read of the carb. Mine was pretty close. One of these days I'm going to make a video on how to tune all the stock components for reference for YouTube.


Yes I do remember bending those rods many years ago. I really never have a fast idle. Only when it feels like it. LOL
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/04/17 09:03 PM

Ooooofff......ok, where to start. Yeah, I've never had points.....oldest two cars I've had were '76 so I'm not sure how much gap the points unit will do. If you start to get misses, I guess that plug gap was too wide.

Yeah, the factory settings on initial idle and advance are different depending on year, transmission, and AC option combo. I've been told to set initial advance at wherever you get the best vacuum at the recommended initial speed. I've heard some set it to 10* and others at 12*. Mine's at 10*, but after I'm done with fluids and the cooling system, I'm checking all my settings again and see what is optimal for mine.

Yeah, as I said in the other thread if the solenoid is frozen, get a new one. Not sure if adjusting the hex screw works in that case? Again, hex screw is tightened all the way in with the allen wrench while holding the solenoid with the other wrench. Unplug, and then begin loosening it and see if the base idle changes.

Yeah, just plug your vacuum gauge in the port to the advance on the distributor, before you set initial idle and advance then the base idle. You don't want the vacuum advance kicking in while you are trying to adjust those. The Thermac air cleaner and vac adv are both plugged into full manifold vacuum port at the base of the Monojet. Mine has a thermal valve and delay on top of the water neck that the vacuum advance runs thought, and I'm not sure what year they started doing that.

The timed vacuum port toward the top of the carb is for the vacuum hose going to the thermal valve attached to the lower water neck. It only opens when the engine if fully warmed up, and the timed port only pulls vacuum while cruising and not idling. So it shouldn't really affect the idle adjustments, but the recommendations tell you to plug it while you are tuning (I never have, and neither has IntegratedJ78). But it then Ys off there to the EGR valve and the EVAP canister. You can live without your EGR and gain some fuel economy by removing that Y in the vacuum line and just connecting to EVAP only. The EVAP canister scavenges the lost fuel vapor from the carb and fuel tank during cruising, so that increases fuel economy. The EGR is there to introduce some exhaust gas to the intake to decrease CO and NOx in the exhaust. So that's why your friend was recommending it. IntegratedJ78 made a plate to cover the EGR port so I could remove my rusty one.

Oh no vacuum gauge? They are good for seeing if you are going in the right direction or not, otherwise just watch engine speed. Yeah, just unplug the hose at the vac adv and stick a golf tee or or a pencil tip into it to plug it while you are working on timing and speed. The vac adv should be plugged into the full manifold vacuum at the base of the carb, unless points are set up different from HEI? Most sources suggest the timed vacuum port for advance, but GM always uses the full port for advance from the factory.

Tell you what, put some pics up that show the routing of the vacuum hoses and distributor/carb on your imagr and post them on the thread. I'll get my account up and running and repost the pics of my '78 routing of everything so we can see what the differences are between those years. I'm curious if anything changed?
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/05/17 11:15 AM

Imgur account activated:



Here's what my engine bay looked like when I bought it.




Cleaning up and replacing parts.




The radiator, fan, and hoses off show all the components well.




early view of the engine bay after cleanup.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/05/17 11:19 AM

Here's some views of the current state of my engine bay. Notice the HEI upgrades and the new hose to air cleaner (they sent the wrong color). The radiator is a plastic/aluminum replacement, but it was already installed when I bought the car.





Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/05/17 11:47 AM

Here's some of the basic upgrades I've made.



Here you can see the original HEI cap and four blade fixed fan. I've already replaced the fuel pump and put an inline filter in the fuel hose going from the fuel line on the frame to the pump (the fuel line from pump to carb is all metal and would need to be cut to add the inline filter).



I added a high quality cap and rotor from BWD, and also got a new coil cap and wire loom to go with it. You can see the new cap, wires, and vacuum advance on the engine in the pic in the previous post.



Here's a pic of the the three blade clutch fan off the later truck 250 and 292. You can see it in the pic in the previous post too.

Not visible is the K&N air filter I added too. Currently the cooling system is apart and being wired for the electric fans to replace the clutch fan.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/06/17 08:41 AM

Originally Posted By: Lifeguard
Ooooofff......ok, where to start. Yeah, I've never had points.....oldest two cars I've had were '76 so I'm not sure how much gap the points unit will do. If you start to get misses, I guess that plug gap was too wide.

Yeah, the factory settings on initial idle and advance are different depending on year, transmission, and AC option combo. I've been told to set initial advance at wherever you get the best vacuum at the recommended initial speed. I've heard some set it to 10* and others at 12*. Mine's at 10*, but after I'm done with fluids and the cooling system, I'm checking all my settings again and see what is optimal for mine.

Yeah, as I said in the other thread if the solenoid is frozen, get a new one. Not sure if adjusting the hex screw works in that case? Again, hex screw is tightened all the way in with the allen wrench while holding the solenoid with the other wrench. Unplug, and then begin loosening it and see if the base idle changes.

Yeah, just plug your vacuum gauge in the port to the advance on the distributor, before you set initial idle and advance then the base idle. You don't want the vacuum advance kicking in while you are trying to adjust those. The Thermac air cleaner and vac adv are both plugged into full manifold vacuum port at the base of the Monojet. Mine has a thermal valve and delay on top of the water neck that the vacuum advance runs thought, and I'm not sure what year they started doing that.

The timed vacuum port toward the top of the carb is for the vacuum hose going to the thermal valve attached to the lower water neck. It only opens when the engine if fully warmed up, and the timed port only pulls vacuum while cruising and not idling. So it shouldn't really affect the idle adjustments, but the recommendations tell you to plug it while you are tuning (I never have, and neither has IntegratedJ78). But it then Ys off there to the EGR valve and the EVAP canister. You can live without your EGR and gain some fuel economy by removing that Y in the vacuum line and just connecting to EVAP only. The EVAP canister scavenges the lost fuel vapor from the carb and fuel tank during cruising, so that increases fuel economy. The EGR is there to introduce some exhaust gas to the intake to decrease CO and NOx in the exhaust. So that's why your friend was recommending it. IntegratedJ78 made a plate to cover the EGR port so I could remove my rusty one.

Oh no vacuum gauge? They are good for seeing if you are going in the right direction or not, otherwise just watch engine speed. Yeah, just unplug the hose at the vac adv and stick a golf tee or or a pencil tip into it to plug it while you are working on timing and speed. The vac adv should be plugged into the full manifold vacuum at the base of the carb, unless points are set up different from HEI? Most sources suggest the timed vacuum port for advance, but GM always uses the full port for advance from the factory.

Tell you what, put some pics up that show the routing of the vacuum hoses and distributor/carb on your imagr and post them on the thread. I'll get my account up and running and repost the pics of my '78 routing of everything so we can see what the differences are between those years. I'm curious if anything changed?


Yeah my solenoid is bad. But...No one sells a replacement for mine. I cannot find one anywhere? Quite odd. Im kinda screwed on that one. I just universal ones that look strange.

I need to get a vac gauge. I got busy here for a few days so I havent been to the store. I was just at harbor freight the other day for just cheap stupid things to keep on hand, I wished I would have grabbed one. I copied down your instructions, I am going to try and get this running better. Its not terrible, but it happens randomly.

I think my carb truly needs a rebuilt, it is a rebuilt one on there, but I have no idea when he replaced it. Looks dirty, so hard to tell.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/06/17 08:45 AM

Originally Posted By: Lifeguard
Here's some of the basic upgrades I've made.



Here you can see the original HEI cap and four blade fixed fan. I've already replaced the fuel pump and put an inline filter in the fuel hose going from the fuel line on the frame to the pump (the fuel line from pump to carb is all metal and would need to be cut to add the inline filter).



I added a high quality cap and rotor from BWD, and also got a new coil cap and wire loom to go with it. You can see the new cap, wires, and vacuum advance on the engine in the pic in the previous post.



Here's a pic of the the three blade clutch fan off the later truck 250 and 292. You can see it in the pic in the previous post too.

Not visible is the K&N air filter I added too. Currently the cooling system is apart and being wired for the electric fans to replace the clutch fan.


I really need to upgrade to and Hei like you did. Everyone seems to do that./ I have new points, and complete tune up. Actually runs very smooth, for except a very slight rough idle in gear, and that fluttering once in a while, when under throttle demand.

Yours looks nice. I need to get some photos of mine. I do have the 4 blade fan. I didn't know if going to the three blade or electric would do much. I see a lot are doing it though.

my stock air cleaner was missing the lid. So I put a open air filter on. One of those Mr. gasket chrome ones from summit. I dunno if that hurt anything doing that. As in....changing the way the carb acts?
Although when I got the car, it was worse. I got it top run better. Just started to do the fluttering recently while under acceleration.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/06/17 01:37 PM

Originally Posted By: Tracker64


I really need to upgrade to and Hei like you did. Everyone seems to do that./ I have new points, and complete tune up. Actually runs very smooth, for except a very slight rough idle in gear, and that fluttering once in a while, when under throttle demand.

Yours looks nice. I need to get some photos of mine. I do have the 4 blade fan. I didn't know if going to the three blade or electric would do much. I see a lot are doing it though.

my stock air cleaner was missing the lid. So I put a open air filter on. One of those Mr. gasket chrome ones from summit. I dunno if that hurt anything doing that. As in....changing the way the carb acts?
Although when I got the car, it was worse. I got it top run better. Just started to do the fluttering recently while under acceleration.


Yeah, for street performance the HEI is pretty good from the factory. Factory coil is all that is needed.

Yeah, all the car 250 inline sixes came with the fixed 4-blade fan from the factory until they discontinued them after 1979. The truck motors came with the same fixed 4-blade fan but had a larger diameter water pump pulley it was mounted to reduce the drag of the accessories. When they went to a 3-blade clutch fan for trucks (I don't remember which year) they used the smaller pulley from the cars. The least parasitic drag combo would be the early truck pulley with electric fans, next best would be the truck pulley and clutch fan. I haven't been able to find an early inline truck pulley, with grooves in the right spot yet for PS and alternator. When I switched from fixed fan to electric fans for a short while, I saw a jump of almost 3mpg in fuel efficiency.....so yeah big difference. I switched to the clutch fan temporarily while I sorted out the electrical issues as I couldn't find a switched wire for the regulator, and just had it wired to the battery and always on but that was too hard on the battery.

Open element air cleaner flows better, but it's sucking hot engine compartment air, so it's mixed bag. My factory THERMAC air cleaner actually has a hose that draws cooler air from in front of the radiator support. But it is right behind the left turn signal. So I removed the assembly, created a duct with reflective inside and a cut out for the turn signal housing, and now i have a stealth ram air duct. The flexible 3" duct I got to replace the factory paper one also allows a pretty direct feed of the ducted air to the air cleaner. My air cleaner probably doesn't flow as well as your open element, but with my K&N filter and cool ram air ducted to it, it's probably probably a tie between the two as far as power and fuel efficiency goes.

I'm just wondering if you capped the vacuum port that feeds the factory air cleaner? The vacuum that actuates the flap in the snorkel is the full manifold port on the bottom of the Monojet. It has a metal Y port with one angled up to supply vacuum to the THERMAC, and one pointing straight out that the distributor vacuum advance is attached to. Did you cap it off or just break the second port off and push the vac adv hose all the way onto it?

Yeah cleaning up the rust and grime is lot of work. You have to get in there with degreaser, toothbrushes, rags, and elbow grease. Sand and rustoleum the rusty parts. It's best to remove as many parts as possible to clean and really get in there. Plus when they are off, it is easier to repaint them. The gold cadmium parts are best replaced or just painted with cast pant. The aluminum and unpainted metal can be clear coated once the oxidation and rust is removed, or painted with aluminum paint and cast iron paint. I use the cast-blast paint for the hinges and other items that have that phosphate coating. Rattle can Chevy engine orange is ok for the engine, but the parts that are close to the exhaust manifold will definitely burn off after awhile. It's best to remove the valve cover, engine lift eyelets, side covers, water neck, even water pump to clean paint those separately. The rest is removing hoses, belts, and wires; or moving and masking them, and spraying as much of the engine as you can reach. When you go to remove head and intake, it's better to paint those with a spray gun and proper engine paint so that they last. That's what I plan to do as the only way to get the GM corporate blue is the canned paint, they actually put Chrysler blue in the rattle cans and label it GM blue.......there's definitely a difference.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/06/17 03:40 PM

I'm going to definitely do an HEI swap soon. I do see a lot of not mostly all have done that.

For the fan I'm thinking electric as long as I can find one that bolts up. I'm sure some fabricating will be involved. The wiring....that's where I'll get lost. On where to wire it up and how to make it come on a a specified temperature.

My vac ports are all hooked up. Odd thing is...when I removed the factory air cleaner. It had a small vac line on it, but nowhere for it to go. Quite odd.
I agree I'm pulling more air with the aftermarket, unfortunately hot air. Ugh

I'll be on my laptop in a few hours.

I found a brand new rebuilt carb still in the box from classic industries on the Craigslist I can grab for about 80.00.

He took photos of all four sides for me. So I took photos of all 4 sides of mine. I have to upload them and post them here. It's for a 69, and mines a 74.

It's missing one vac port that goes to my charcoal canister. I don't think that's important? And the throttle linkage looks a little different, at least to me. Maybe it can still be used.

I'll upload both carbs of all 4 sides and maybe you can tell me if it would work?
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/06/17 05:40 PM

Okay here we go!! LOL

If this carb can be made to fit, then I may grab it for 80 bucks, its never been mounted.

It looks different to me at the throttle linkage, and also there is no place for a choke pull off. So I don't know how my choke would work. This is for a 69. Mine is a ...74.

His is missing the top vac port. On mine it only goes to the charcoal canister. SO maybe thats not a big deal?

The bottom port on his is like mine, goes to vac advance. Hopefully on his, its the same "type" of portto make the vac advance work properly...

Here's His...



Here's mine....



His...Looks the same there, same vac port..



Mine....



His.....



Mine...



Okay....Now one more confusion...His throttle linkage looks different for a 69. And my return spring is set different.... I dunno??



Mine.....






Here's the box with the part number. I dunno if that helps..



.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/06/17 06:11 PM

Just a photo of my engine for reference....

Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/08/17 12:05 AM

Alright, I can see your kick down linkage for your auto. And is see that there is no AC and no power brakes just like mine. Nice valve cover there. wink I'll put up some HEI and electric fan pics later.

For the carbs, your factory carb looks similar to mine, but there are some odd differences. I can't see where the lines for the EGR and EVAP (charcoal) canister are going or coming from. Could you get a pic of the front of the engine and over the EVAP canister so I can figure out how your hoses are running? Alright I got a few more pics of my carb:



First here's a pic of my air cleaner and a lot of other things off so you can see how everything routes. I have the factory assembly manual, so I have checked all the attachments to make sure they are correct. I'm putting it on top so it is right below your engine pic in the message above so you can see them both.



I don't have pic of the front of my carb, but here is the passenger side of it. You can see the solenoid is there like yours, but I have an electric choke there and you have a hose going somewhere? You also have what I guess is the timed vacuum port on this side, which should be running to both the EGR and EVAP (charcoal) canister? It's hard to see, but it looks like you have the main EVAP hose and PCV hose running to a vacuum port on the manifold in the same place as mine.



Here's the rear of my carb. Aside from the lack of an electric choke on yours, it looks the same to me. The EFE vacuum line appears to connect to a port at the base of your Monojet, while on mine there is a vacuum port on the manifold for it.



Ok, here is a shot of the driver side of my carb. Right away on the upper top right you see a port that is not on yours. This is a timed vacuum port and it runs to a thermal valve on the water neck which then runs to the EGR and EVAP. On the upper left side is a hose on mine that vents the fuel bowl to the EVAP to prevent fuel vapor in the bowl from being released to the atmosphere. On your's someone has capped it.....which there really is no reason to as this just passively collects fuel vapor from the carb when parked and keeps it from smelling up your garage. The Holly 390cfm has bowl vents that just vent straight up so this hose is useless once you switch (although you could drill a hole in the bottom of the air cleaner and get a port to seal it too and hook the hose to try to collect any vapor settling on the bottom of the air cleaner).

On the top of the pic you see the bottom of my air cleaner and the hose running from there to full vacuum port at the base of the carb in a tee fitting with the vac adv line too. I suspect this is where your dangling air cleaner vac line plugged in too, but someone broke that part of the tee off and pushed the vac adv hose all the way on to cover the hole. Pull it off and see if there is a broken off port tee there.



Here is a labeled pic of how the hoses function. It's hard to see the lines running from the PCV and EVAP to the manifold port which has a tee fitting as well.



And here is the 1978 49-state diagram of how everything runs. I made notes on for a Holley-390/Offy/Stovebolt swap as to which hoses can be retain and what they will plug into, and which need to be deleted.



Here's my labels where the hoses go on the Holley 390cfm for the swap.



Here's one more shot to show how the '78 is set up. You can see two thermal valves screwed into the water neck. One on top is attached to a delay valve in the line running from the distributor vacuum advance to the full vacuum port on the bottom of the Monojet.

The second one is on the bottom half of the neck and has one line running from it to the vacuum source on the carb which is the top timed vacuum port. The other line runs a few inches and then has a red plastic Y to split the line with one going to the EGR. The other line goes to the EVAP canister where there it plugs into one of the two valves on top of it (I forget which one, need to snap a pic of that).

I hope that helps. Take some pics of the front of your engine and the EVAP (charcoal) canister and I can see how your hoses are routed, because they are not quite the same as mine.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/08/17 06:52 PM

Okay I gave it my best! LOL I only got to remove the valve cover so far. I haven't had the car long. I hope these photos help. I labeled them the best I could.

The prior owner had a rebuilt carb put on, but probably quite a while ago. He seemed to understand cars, but I wouldn't call him a mechanic. So if he messed up the vac lines, I wouldn't be surprised.











Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/08/17 08:48 PM

I'm going to have to study your hose layout more, but here's a few quick observational differences I see.

The EVAP (charcoal) canister is different from mine. It is like a V8 canister and not the L6. maybe they changed, or maybe the carb or canister are not original. The V8 only has one vac valve on top because the second one is built into the 2GC or Qjet bowl. The Monojet just has the single port above the bowl that leads to the second vac vent on the EVAP canister.

It looks like the full manifold vacuum port on the driver side, which is the vac-adv/THERMAC on mine, is the EGR port on yours. My EGR is run off a timed port on top. This must have been a change later, maybe when the catalytic converter was introduced. The thermal valve for your EGR is located on top of the water neck, which is where the thermal valve is for my distributor vac adv.

I see your distributor vacuum advance just goes straight to the advance canister without a delay valve or a thermal valve on it. It's on the bottom so this should be a a full manifold vacuum port too.

I forgot about the Th350 vacuum line. Too used to a manual now.

Yeah, the port on the manifold sucks fuel vapor from the crankcase through the PCV and fuel vapor from the EVAP (charcoal) canister to mix with the income air/fuel mixture.

There's a lot of electrical tape on the wires above the intake. Looks like someone pulled the plastic wire housing off them and just taped them up afterwards.

Notice the hose coming off the EVAP (charcoal) canister and running over the inner fender and disappearing beside the firewall? That's the line to the fuel tank. When I got my Camaro it was there but disconnected from the metal line. Stunk up the garage with gas vapor like you can't believe. The EVAP (charcoal) is worth keeping just for this reason alone. Plus it saves gas instead of venting it to the atmosphere......gas you paid for, why would someone do that? :P

I'm still wondering about the lack of an electric choke on your Monojet? Was there a heated coil choke on the Monojets earlier like the 2GC? I don't see where it is housed if there is one?
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/08/17 09:07 PM

BTW, to delete your EGR, you just need to cap the vacuum port on the carb. You can just pull the hoses then, as the valve stays shut without vacuum and no exhaust enters the intake. You could take the thermal valve off the water neck and just put a plug in it too. If you want to go far enough, you can make a plate to cover the opening after removing the EGR valve. But once you throw the Offy and Holley 390cfm on it, there is no place on the Offy for the EGR anyway.

BTW, just noticed the blue color of the Nova, I like that color.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/08/17 10:57 PM

Thank you its the factory midnight blue.

He did replace the carb sometime ago. So who knows when you buy a rebuilt what your really getting.

My EGR goes to that switch on the thermostat housing. My buddy did tell me to unplug the EGR and cap that hose off. He said I would notice a slight difference.

I'll chase that canister hose and see where it goes. I just assumed it went back to the gas tank. I'll see where its going. I do smell gas once in a while right after turning off the car walking past it in the garage. But I have no leaks anywhere.

The prior owner replaced the head gasket with the guidance of a buddy. So who knows if they have some of the hoses hooked up wrong. Very possible just from talking to him.

I checked the numbers on the carb and its for a 1976 chevy C10 manual truck. However...I cant go by that with a rebuilt. They just throw parts together from a bunch of carbs.

Theres a spring heated coil the has an arm that leads up to my choke from the manifold. But I don't believe that or the choke pull off is working. I have no electric choke.

Thats why I was considering that carb that I showed photos of previously on this thread. But...the throttle arm linkage looks different I showed it on my post.if you scroll back youll see what I mean.

Should my hose coming from the vac advance have constant vacuum or only under throttle? I can test that tomorrow.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/09/17 12:47 PM

Yeah, it makes sense that maybe the carb was a later carb and the EVAP (charcoal) canister is the original. And that the electric choke was removed and the fuel bowl vent was capped.

Yeah, my hose was pulled off the metal line to the tank right under the hood hinge. The first emissions they controlled was the fuel vapor that escapes into the atmosphere and stinks up garages. The fuel tank first the vent in the cap changed to a one way vent, then it was unvented and the EVAP canister added to capture the fuel vapors. The carbs were also vented to the EVAP at some point, but from yours it looks like maybe that happened later. And of course the blow-by vapor in the crankcase which the PCV valve was added to close up the crankcase so it didn't vent to atmosphere.

So you have three places you might smell fuel vapor from. The carb which now has an open element air cleaner, so fuel vapor in the bowl just leaks out there. The valve cover breather which used to attach to the air cleaner so vapor would go there (probably not much when engine is off). And of course the line from the fuel tank to the EVAP (charcoal) canister.

I'm still trying to find a diagram for your hose layout online. I found another one for my year which is a pretty good one showing how the top of the EVAP canister looks different, and the THERMAC line attaching in the same spot as the vacuum advance line (front of engine is to the left, driver side is bottom).



Oh, he had the head off too? Probably used the standard rebuilder gasket with 0.040" thickness, which means your CR was reduced. Aside from the radiator swap and the factory carb rebuilt, my Camaro was completely unmolested. Although they had switched the vacuum hoses for the EGR/EVAP and THERMAC around, and switched the #3 and #4 spark plug wires. But I caught those goofs before I really got it running again. Good to have the factory assembly manual.

Ah ok, that heated spring in the manifold sounds like a similar setup as what they did for the 2bbl V8 with the 2GC carbs. That's why it wouldn't need the electric choke. My guess is that the difference between your layout and mine occurred in 1975 when they introduced the catalytic converter and the integrated cylinder head (intake and cylinder head combined into one casting). But 1974 may have had some of the changes due to the HEI as well. I gotta find some diagrams to see when they changed what. I find the running changes really interesting.

GM only use full manifold vacuum for their HEI. I'm not sure if the placement of your points vacuum line is full/manifold or ported/timed vacuum. It's a little higher on the carb body, while the EGR port is low on the throttle body base. The spot where your EGR is plugged in is where my vacuum advance and THERMAC hoses are plugged in. So maybe you should repurpose that port for your HEI when you swap to make sure you have full vacuum. But mine also has a distributor TVS (thermal vacuum switch) with a delay valve attached as well.

Two things I am not seeing on your engine are the EFE system and the heat stove on the exhaust manifold? Does your's have the EFE flapper valve on the exhaust manifold that redirects exhaust to the bottom of the intake manifold during warmup? There should be a vacuum canister that actuates it and a vacuum port for it on the manifold? Maybe this was a later edition too, and the intake heating was just passive on yours? There should also be a metal shroud attached to the exhaust manifold with a round fitting that a rigid metal tube attached to and then ran up underneath the snorkel of your air cleaner? The flapper valve in the snorkel has a vacuum hose that runs to a vacuum switch in the underside of the THERMAC air cleaner and then a second hose to a vacuum port on the carb? You said you had a mystery hose on your air cleaner, so I assumed it was to the THERMAC flapper valve in the snorkel? Unless maybe you were talking about the hose that runs to the breather filter in the side of housing that used to connect where your valve cover breather is now? Take a pic of your air cleaner and I can tell you which hose it is.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/09/17 03:05 PM

I'll respond to your post longer a little later I'm actually in the garage using my phone. So it makes it hard for me to respond to all the comments.
M
That guy just texted me and told me I could have that brand new carburetor for 50 bucks. The one that I have in my previous posts with the photos. I showed a comparison of all four sides of both of our carburetors in the post.

It's really tempting I could probably figure out the throttle linkage. But I realized one thing.

There's no port on the base plate for my automatic transmission modulator valve. I don't know if there's a way around that. If you scroll back you'll see the photos of the carburetor he has.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/09/17 03:40 PM

There's really kind of a hole in diagrams for hose layouts in the mid '70s, specifically '74 and '75 are completely absent.

The only diagram I can find for 1973 is this one for the Vapor Control (EVAP or charcoal canister):


here's a 1976 diagram of the EFE route (this is identical to my 1978 layout), but I can't find a diagram of the rest of the lines:


The 1977 diagram is interesting, as it looks like the layout of your 1973 EVAP remained unchanged through '77. The EFE is there, and the advance is similar to your layout:


The 1978 and 1979 diagram are identical to this one I posted earlier. My year seems to be the one with the most changes. The vacuum advance was given a TVS and delay valve and the EVAP got a vent from the fuel bowl with it's own valve.


Here's my EVAP canister for 1978 and 1979. Please excuse the dust and dirt, it's been sitting for a year now while I get back to finishing all the fluid changes, coolant upgrade , and fixing the exhaust. You can see they added an extra vacuum valve on it that the fuel bowl vents to. The line to the fuel tank is between them:


And then here is that fuel line running under the hood hinge where someone had disconnected it, making my garage smell like a fuel can:


And I snapped a couple shots of my THERMAC air cleaner with the vacuum hoses attached:



I looked behind my electric choke and there is no hose where there is one for your choke. Where your vac adv and the EVAP (charcoal) line plug in there are two holes in the body of the carb but no ports. Must be internally plugged.


Here's the tee port on my base throttle body with the hose to the THERMAC off, and the hose to my vac adv (through the TVS and delay valve along the way) attached. On your's the EGR is plugged in here:


I also got a shot of the front of my carb while I was at it:
[img]http://i.imgur.com/CzRPkCg.jpg[/img]
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/09/17 05:34 PM

Thank you so much I'm leaving work right now as soon as I get home Ill get on my laptop so I can see the photos better.
Let me know what you think of my post above yours with that carburetor situation. I don't know whether to purchase it or not.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/10/17 10:10 AM

Okay I'm going to study your vac line diagrams. Thank you so much. That will help me a lot.
I am off today so I went into the garage. I don't think I have a carb issue. Although I do want to go over them vacuum lines according to your chart.

I have an intake gasket leaking. I know the prior owner had tried to replace it, and I think he screwed up.
When I got the car it was leaking there and I snugged it up and it stopped leaking, but now the leak is back.

I have a new intake gasket and exhaust gasket set by Fel-Pro on hand. Never change them before it looks like a lot of juggling.

There's a YouTube clip I made from my phone I don't know how well you'll be able to hear it starts stumbling when I hit it with carb spray there. It's towards the back near the firewall. I did the best I could with the video so I don't know if you'll be able to tell or not. But soon as I spray that area the whole motor start shaking and Idle drops down lower. Here's the clip.

https://youtu.be/BH2p184jmV8


.



.


Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/10/17 09:53 PM

Sounds like a reasonable diagnosis. Yeah, keep the bolts and hold downs sorted to which holes they go to, they are not all the same and have a specific order.

I wasn't sure what you need the new carb for, there wasn't a lot on it as far as enough vacuum ports for everything and and the missing choke linkage and vacuum can that you would have to transfer over? And you said your solenoid was not working, so if that is still the case then you would need a new one with either your current carb or the new one?

BTW, I think after looking at my carb, yours, and the diagrams I have the passenger side vacuum ports figured out. Starting with the choke vacuum, your can draws from a port that is behind my electric choke, so my can actually draws from another port closer to it. I assume this is a timed vacuum port due to how high up on the carb it is. My carb has two plugged holes below the electric choke, while your's has the EVAP (charcoal) plugged into the top one and the distributor vac adv into the bottom one. On mine and in the '77 diagram the EVAP is located high on the other side and is timed vacuum, while the advance is coming off the low full port that your EGR uses. So my guess is despite how close those two ports on yours is, the upper one is timed for the EVAP and the lower full for the vac adv. Inside, they are drawing vacuum from opposite ends of the carb. For some reason in '73 the EGR was full manifold vacuum, and by '77 at the latest it was timed vacuum. BTW, do you have the EFE flapper valve on the exhaust manifold?

Turn your phone sideways to widescreen so the viewer can see everything, I like to ogle while I listen. wink I think I hear the change when you spray it. The intake sealing was a common problem on inline Chevys, that's why they went to an integrated head and intake from '75 to '78. But then they had head cracking issues and put the non-integrated top end back on for '79.

I did the exhaust on mine for IntegratedJ because he wanted to know what the Z28 exhaust sounded like on it. I did some under hood video but I guess I didn't upload that:

https://www.youtube.com/watch?v=cxzW7miIM6s
https://www.youtube.com/watch?v=yMySPecpiJA

I really want to do a tuning how-to video for the inline six when I'm done organizing the garage and got it back together again.
Posted by: gbauer

Re: Chevy 250 hp confusion - 08/11/17 08:25 AM

If you're going to change the gasket use some high temp copper RTV on it. You'll get a much better seal.



When you do it clean both sides of the flanges, smear it on both sides of the gasket, give it 15 minutes, put it on, put on the headers and intake, snug everything but don't torque it down yet, then wait until the next morning to torque down the nuts on your studs. This will ensure a good seal.

I had a heck of a time getting mine to seal until I heeded the advice of my elders here and used the RTV.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/11/17 10:31 PM

Originally Posted By: gbauer
If you're going to change the gasket use some high temp copper RTV on it. You'll get a much better seal.

When you do it clean both sides of the flanges, smear it on both sides of the gasket, give it 15 minutes, put it on, put on the headers and intake, snug everything but don't torque it down yet, then wait until the next morning to torque down the nuts on your studs. This will ensure a good seal.

I had a heck of a time getting mine to seal until I heeded the advice of my elders here and used the RTV.


Good tip. No leaks on my integrated exhaust manifold, so i don't need it until I swap the whole top end at once. All at once kind of thing.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/13/17 09:42 PM

Originally Posted By: Lifeguard
Sounds like a reasonable diagnosis. Yeah, keep the bolts and hold downs sorted to which holes they go to, they are not all the same and have a specific order.

Sorry for the delay. I got stuck working 16 hour shifts, because people are lazy and call off work! Ugh!!!

Anyhow! I am wondering when this guy and his buddy did the head gasket, if they mixed them up. I noticed the one nut towards the front of the engine doesn't have much thread.."stud" sticking out of it.


I wasn't sure what you need the new carb for, there wasn't a lot on it as far as enough vacuum ports for everything and and the missing choke linkage and vacuum can that you would have to transfer over? And you said your solenoid was not working, so if that is still the case then you would need a new one with either your current carb or the new one?

I did decide against his carb. If I have to, I may rebuild mine. I see that Mikes carb parts, sells the kits. And even a new float. No solenoid for mine though. I can't find one anywhere.
They all look odd.
My carb that is on there, the numbers come back to a 76 Chevy C10 though, with manual tranny. But I also can't go by that. They seem to just slap a bunch of "mixed bag" parts together sometimes when their rebuilding carbs on a assembly line.


BTW, I think after looking at my carb, yours, and the diagrams I have the passenger side vacuum ports figured out. Starting with the choke vacuum, your can draws from a port that is behind my electric choke, so my can actually draws from another port closer to it. I assume this is a timed vacuum port due to how high up on the carb it is. My carb has two plugged holes below the electric choke, while your's has the EVAP (charcoal) plugged into the top one and the distributor vac adv into the bottom one. On mine and in the '77 diagram the EVAP is located high on the other side and is timed vacuum, while the advance is coming off the low full port that your EGR uses. So my guess is despite how close those two ports on yours is, the upper one is timed for the EVAP and the lower full for the vac adv. Inside, they are drawing vacuum from opposite ends of the carb. For some reason in '73 the EGR was full manifold vacuum, and by '77 at the latest it was timed vacuum. BTW, do you have the EFE flapper valve on the exhaust manifold?

I'll have to see if theres a flapper valve. But I never noticed one. I have that little shell with the hole for the pipe that goes up to the air cleaner. Kinda like from the exhaust, to heat the carb I am guessing. I disconnected my EGR, and plugged that port on the switch on the Thermostat housing. they sure did a lot of moving around with the vac lines over the years.


Turn your phone sideways to widescreen so the viewer can see everything, I like to ogle while I listen. wink I think I hear the change when you spray it. The intake sealing was a common problem on inline Chevys, that's why they went to an integrated head and intake from '75 to '78. But then they had head cracking issues and put the non-integrated top end back on for '79.

I'll take a video and kind of move around the whole engine tomorrow. I'm off tomorrow. I'll rev it up...etc. I need some vac caps. I plugged a few hoses, and it helped a bit. I snugged the intake down again!! Unreal! Anyhow, I will get the new gasket on soon. I was going to actually take a extra day, and wire wheel it, and paint it while its off. I never did one on these motors, so hopefully I don't need a second set of hands while installing the gasket.

I did the exhaust on mine for IntegratedJ because he wanted to know what the Z28 exhaust sounded like on it. I did some under hood video but I guess I didn't upload that:

https://www.youtube.com/watch?v=cxzW7miIM6s
https://www.youtube.com/watch?v=yMySPecpiJA

Thats sounds nice!! I want mine to sound like that. Is that langdon headers, or?? And what kind of mufflers. I can't believe how good that sounds!!

That would be great, I would be watching that!!

I really want to do a tuning how-to video for the inline six when I'm done organizing the garage and got it back together again.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/13/17 09:45 PM

Originally Posted By: gbauer
If you're going to change the gasket use some high temp copper RTV on it. You'll get a much better seal.



When you do it clean both sides of the flanges, smear it on both sides of the gasket, give it 15 minutes, put it on, put on the headers and intake, snug everything but don't torque it down yet, then wait until the next morning to torque down the nuts on your studs. This will ensure a good seal.

I had a heck of a time getting mine to seal until I heeded the advice of my elders here and used the RTV.


I have never tried that! I did see someone using that on a car show I was watching. I think it was the spray on copper. I am not big on spray stuff though. I would rather smear it on by hand.
I am glad you added this. And I appreciate you explaining the way to use it. I would have put it on and just torqued it down.
I need to find the tightening sequence and torque for it. I will remember now to do it the way you described. Thank you!
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/14/17 01:42 AM

Yeah, easy to get distracted. My project is on delay until I get the garage squared away for access, and that's only after I get done with yard work, fencing, and back deck.

Yeah, it is pretty easy toe mix the bolts up on the manifolds. I'll try to find my notes on which ones are which lengths and torquing order.

Hmmmm.....'76. I don't have a diagram for that on the EVAP, but the '77 doesn't show a float bowl vent. But yours has one? Maybe mix and match parts. Looks like the top with the float bowl vent was a '78 and later addition.

Yeah, the little shell on the exhaust manifold is to warm the air for the stove pipe going to the THERMAC air cleaner. So sounds like the air cleaner in '73 was the same as '78/'79 at the end of the car run.

You can cap the EGR line right at the carb. The TVS on the water neck just has a valve in it that opens when the engine is hot enough. It won't hurt anything to leave the ports open, and you can just remove it and put a plug in there later. My TVS for the EGR is actually on the side of the lower water neck, and the top hole has a TVS with delay valve for the dist vac adv.

'73 may have been too early for the EFE flapper exhaust manifold.

Yeah if you got it off, you might as well make it look pretty.

Thanks, but my exhaust is still the factory exhaust manifold attached to the 2nd version integrated cylinder head/intake. In '75 when they put the catalytic converter and integrated head on, they increased the exhaust manifold and header pipe to 2.25" and routed under the engine to the passenger's side to run back to the cat. The guy before me cut everything from the catalytic converter on back off. So I just have a 2.25" to 2.5" piece on the end going to a 2.5" pipe in place of the cat. Then from there on back it is the '77 to '81 Z28 cat-back exhaust. A 2.5" flange splitting into a Y of dual 2" pipes to dual resonators. The resonators exit through dual 2.25" tailpipes. Except for the two resonators, it is just open pipe. It's still identifiable as a six since all the cylinders empty through one header pipe. But when you put a dual exhaust with headers and no crossover, you get a different sound of rap-rap from the inline. A crossover will make it sound more like mine. Whichever is to your taste.

Yup yet another project. But once I get everything changed and running again, I could just film my tuning.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/17/17 05:12 AM

Finally found my notes on the intake and exhaust bolt pattern:

Posted by: stock49

Re: Chevy 250 hp confusion - 08/17/17 06:47 AM

It's a good thing to have three carbs blocking the view :-)
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/17/17 12:46 PM

Originally Posted By: stock49
It's a good thing to have three carbs blocking the view :-)


Yeah, I don't remember who posted that. Obviously someone with a tri-manifold. But that should help sort his retainers out.
Posted by: preacher-no choir

Re: Chevy 250 hp confusion - 08/21/17 06:42 PM

3.08 gears are the "kiss of death" for these sixes, a very good rear gear ratio is a 3.55--very well rounded ratio--it will wake up the smallish motor and let it run more freely--if you do this first it may save you a lot of motor hop-up spending--it's really a wake-up move. The original '62 Chevy lls were equipped with 3.55s, then in '63 they switched to 3.08s and performance plummeted. I had a '63, and the '62s would embarrass me. Switched to a 3.55 and wow what a difference--almost like going from a two-speed PowerGlide (1,82 low gear) to a three speed Turbo hydramatic (2.54 low gear)when you hit the "go" pedal---OOOOPS--I see now I came 'waaay too late with my suggestion!!
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/21/17 10:02 PM

Originally Posted By: preacher-no choir
3.08 gears are the "kiss of death" for these sixes, a very good rear gear ratio is a 3.55--very well rounded ratio--it will wake up the smallish motor and let it run more freely--if you do this first it may save you a lot of motor hop-up spending--it's really a wake-up move. The original '62 Chevy lls were equipped with 3.55s, then in '63 they switched to 3.08s and performance plummeted. I had a '63, and the '62s would embarrass me. Switched to a 3.55 and wow what a difference--almost like going from a two-speed PowerGlide (1,82 low gear) to a three speed Turbo hydramatic (2.54 low gear)when you hit the "go" pedal---OOOOPS--I see now I came 'waaay too late with my suggestion!!


I assume that is a recommendation for the auto equipped cars, or at least the 2.85:1 3spd through 1974. In 1975 to 1977 they had a 3.11 first gear, and then 1978 and 1979 had the 3.50 first gear. 3.55 is a bit deep for those wide ratio gear boxes.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/22/17 08:11 PM

Originally Posted By: Lifeguard
Finally found my notes on the intake and exhaust bolt pattern:



Thank you! I appreciate that. I will try to see if he had them on wrong, I am quite sure he did. Some of the nuts are right at the edge of the threads.

I have been on my wifes Subaru, I think I am almost done, and can get back on the Nova. I keep starting it up an letting it run every 3 days. But I keep a battery tender on just in case. LOL
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/22/17 08:13 PM

Originally Posted By: stock49
It's a good thing to have three carbs blocking the view :-)


Hahah...Theres a guy near me selling a offy intake with dual one barrels, but he wants 500 bucks! And basically the carbs are free, because their probably worn out. Thats kind of a high price
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/22/17 08:17 PM

Originally Posted By: preacher-no choir
3.08 gears are the "kiss of death" for these sixes, a very good rear gear ratio is a 3.55--very well rounded ratio--it will wake up the smallish motor and let it run more freely--if you do this first it may save you a lot of motor hop-up spending--it's really a wake-up move. The original '62 Chevy lls were equipped with 3.55s, then in '63 they switched to 3.08s and performance plummeted. I had a '63, and the '62s would embarrass me. Switched to a 3.55 and wow what a difference--almost like going from a two-speed PowerGlide (1,82 low gear) to a three speed Turbo hydramatic (2.54 low gear)when you hit the "go" pedal---OOOOPS--I see now I came 'waaay too late with my suggestion!!


I don't know what kiss of death meant?

I would like to change the rear gears first. I imagine a nice gear ratio for my posi, would wake it up nicely.

Honestly, I seen Summit sells gear set ups for my 8.5 posi, their not cheap.

And..I will admit I have never done a swap with gears. I think you have to do certain things inside there, and something about the large nut on the pinion. I think I would have to pay for that one thing to get done. I know I would not get everything right on that. But yes...I agree, there would be a major difference.
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/22/17 08:19 PM

Originally Posted By: Lifeguard
Originally Posted By: preacher-no choir
3.08 gears are the "kiss of death" for these sixes, a very good rear gear ratio is a 3.55--very well rounded ratio--it will wake up the smallish motor and let it run more freely--if you do this first it may save you a lot of motor hop-up spending--it's really a wake-up move. The original '62 Chevy lls were equipped with 3.55s, then in '63 they switched to 3.08s and performance plummeted. I had a '63, and the '62s would embarrass me. Switched to a 3.55 and wow what a difference--almost like going from a two-speed PowerGlide (1,82 low gear) to a three speed Turbo hydramatic (2.54 low gear)when you hit the "go" pedal---OOOOPS--I see now I came 'waaay too late with my suggestion!!


I assume that is a recommendation for the auto equipped cars, or at least the 2.85:1 3spd through 1974. In 1975 to 1977 they had a 3.11 first gear, and then 1978 and 1979 had the 3.50 first gear. 3.55 is a bit deep for those wide ratio gear boxes.


mine has the 3 speed auto 350 turbo. no overdrive, so I do need to pick the right set when I am ready. I seldom do highway, but there are times I do a consistent 50mph. The 308's really stink.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/22/17 10:16 PM

Originally Posted By: preacher-no choir
3.08 gears are the "kiss of death" for these sixes, a very good rear gear ratio is a 3.55--very well rounded ratio--it will wake up the smallish motor and let it run more freely--if you do this first it may save you a lot of motor hop-up spending--it's really a wake-up move. The original '62 Chevy lls were equipped with 3.55s, then in '63 they switched to 3.08s and performance plummeted. I had a '63, and the '62s would embarrass me. Switched to a 3.55 and wow what a difference--almost like going from a two-speed PowerGlide (1,82 low gear) to a three speed Turbo hydramatic (2.54 low gear)when you hit the "go" pedal---OOOOPS--I see now I came 'waaay too late with my suggestion!!


I don't know what transmissions they were using in the early '60s, but I know the history of the 250 inline in the Camaro and finally made it into a chart:



Assuming they were using the same 2.85 first gear Saginaw 3spd in the early '60s, then for those of us with the later wider 3spd:

Saginaw 3spd std: 2.85std & 3.08 rear = 3.11wide & 2.73 = 3.50superwide & 2.56
Saginaw 3spd perf: 2.85 & 3.36 = 3.11 & 3.08 = 3.50 & 2.73
Sag 3spd hi-perf: 2.85 & 3.55 = 3.11 & 3.36 = 3.50 & 3.08

I don't know how to compare these to the powerglide and TH350, as there is the automatic torque difference? But a 3.08 may be a "kiss of death" for the standard Sag 3spd with its 2.85:1 first gear, but for my setup of '78 3.50:1 first with 2.73 rear it would actually end up being deeper ratio for 1st than the standard Sag with 3.55 rear.

I'm not sure if you can compare the powerglide to the TH350 directly just by the combined ratio. But just doing the math here's how the 1.82 powerglide compares to the 2.52 TH350. Which remembering my second Camaro with a 305cid with a TH350 and open 2.73, does not seem all that hi-po:

auto std: Pglide 1.82 & 3.08 = TH350 2.52 & 2.22(?)
auto perf: Pglide 1.82 & 3.55 = TH350 2.52 & 2.56
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/23/17 12:37 PM

I was giving the observations about powerglides, 3.08 gears, 3.55 gears, and the TH350. So i looked at it from a different angle, comparing the combined first gear ratio based on Preacher-No Choir's observations:

Powerglide 1.82 & 3.08 rear: 5.61:1 combined ratio
Powerglide 1.82 & 3.55 rear: 6.46:1 combined ratio
TH350 2.52 & 3.08 rear: 7.76:1 combined ratio

Preacher said replacing a 3.08 with a 3.55 was almost like going to a TH350. The TH350 with 3.08 is definitely a deeper first gear than even the Powerglide with the 3.55. The math seems to indicate that the TH350 is better than the Pglide/3.55 even with the "kiss of death" 3.08. Not sure how that helps with picking a deeper gear tho?

I'm not sure what axle the Nova has, the L6 post 1970 Camaros all came with a GM Corporate 10 bolt rear and only 2.56, 2.73, 3.08, 3.42, and 3.73 from the factory. No 3.55 like the early SD 10 bolts had.
Posted by: panic

Re: Chevy 250 hp confusion - 08/27/17 08:04 PM

Lest we confuse this with the very useful "crawl ratio" doctrine for anticipating low speed manners in traffic with standard transmission:
"The 1st gear ratio times the axle ratio should be above 10 for best results".
Example: 2.20:1 close-ratio Muncie with 3.08 axle = misery at 6.8, the 2.52:1 box is preferred here. The 2.95:1 T5 box works well with anything above 3.23.

How does this compare with the auto trans numbers? They all look too low? The missing factor:
1. stall speed means the engine never lugs.
2. the converter's 2:1 (more or less) torque multiplication adds mechanical advantage during roll out.
Posted by: Blackwater

Re: Chevy 250 hp confusion - 08/28/17 06:25 AM

Originally Posted By: Lifeguard
I was giving the observations about powerglides, 3.08 gears, 3.55 gears, and the TH350. So i looked at it from a different angle, comparing the combined first gear ratio based on Preacher-No Choir's observations:

Powerglide 1.82 & 3.08 rear: 5.61:1 combined ratio
Powerglide 1.82 & 3.55 rear: 6.46:1 combined ratio
TH350 2.52 & 3.08 rear: 7.76:1 combined ratio

Preacher said replacing a 3.08 with a 3.55 was almost like going to a TH350. The TH350 with 3.08 is definitely a deeper first gear than even the Powerglide with the 3.55. The math seems to indicate that the TH350 is better than the Pglide/3.55 even with the "kiss of death" 3.08. Not sure how that helps with picking a deeper gear tho?

I'm not sure what axle the Nova has, the L6 post 1970 Camaros all came with a GM Corporate 10 bolt rear and only 2.56, 2.73, 3.08, 3.42, and 3.73 from the factory. No 3.55 like the early SD 10 bolts had.


One thing to remember about the PowerGlide is that it takes approximately 19 fewer horsepower to run it as opposed to the turbo and other transmissions. Years ago, we swapped out a turbo 400 for a PG and picked up .200 second with NO other changes. We even used the same torque converter by installing a turbo input shaft in the PG!!

The Glide isn't as streetable in a heavier car, but in a small, light vehicle and set up right, it presents some interesting possibilities!!
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/28/17 07:10 AM

Originally Posted By: panic
Lest we confuse this with the very useful "crawl ratio" doctrine for anticipating low speed manners in traffic with standard transmission:
"The 1st gear ratio times the axle ratio should be above 10 for best results".
Example: 2.20:1 close-ratio Muncie with 3.08 axle = misery at 6.8, the 2.52:1 box is preferred here. The 2.95:1 T5 box works well with anything above 3.23.

How does this compare with the auto trans numbers? They all look too low? The missing factor:
1. stall speed means the engine never lugs.
2. the converter's 2:1 (more or less) torque multiplication adds mechanical advantage during roll out.


I hadn't heard about the 10:1 combined crawl ratio. It seems to consistently be the rear ratio that I call the hi-perf which is 2 steps deeper from the factory standard ratio:



My stock manual setup yields a 9.55:1 combined ratio which is close to the 10:1. My own experience with the stock engine is that it connects well from the crosswalk, but it is already bogging and wants to shift by the other side of the intersection. Then it rides 2nd up to 35 and starts to complain again until I can shift at cruising speed. So maybe it is asking me for that 3.08 rear. Then again maybe it just wants more advance or carb, we'll see how it behaves when I change those. IntegratedJ78 thinks it wants the extra gear of a Sag 4spd to go to.

Yeah, I knew there was something different with the auto. That makes more sense as to why they never changed the ratios in the TH350 despite the rear axle gearing getting higher for economy in the '70s. The Saginaw 3spd and 4spd manuals kept getting deeper and deeper 1st gears and that was to overcome the change to more highway economy friendly rear gears.

The slush-box just didn't need the gearing change......but so what is the optimal ratio that TonyPA is looking for then if crawl ratio is not important to his TH350?

Afterthought: Is the crawl ratio recommendation based on car tire size then? Because the Camaros and Novas came standard with E78-14/FR78-14/P205-75r14 which measures at 26" diameter. I know the larger cars like the Monte Carlo used the P215-75r14 tires, but I don't know what the standard size for truck tires was then? Obviously much taller.
Posted by: panic

Re: Chevy 250 hp confusion - 08/28/17 04:46 PM

maybe it just wants more advance
Yes, many times, but it has to be added manually (and subtracted from the mechanical advance) and carefully - but generally helpful.
26" is presumed for passenger cars.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/28/17 05:16 PM

Originally Posted By: panic
maybe it just wants more advance
Yes, many times, but it has to be added manually (and subtracted from the mechanical advance) and carefully - but generally helpful.
26" is presumed for passenger cars.


That's what I thought. 10:1 combined crawl ratio with 26" tires. Adjust the ratio accordingly for tire size increase.
Posted by: Mean buzzen half dozen A.K.A. Hank

Re: Chevy 250 hp confusion - 08/28/17 05:52 PM

If you install a TH350 over a PG in any stock inline car or truck, the PG will be slower.
Posted by: panic

Re: Chevy 250 hp confusion - 08/29/17 01:16 PM

There is one condition in which the PG is more satisfying: kicking down at (roughly, depending on the application) 50 mph will engage 1st (1.82:1) and accelerate better than the TH which can only catch 2nd (1.52:1), so torque multiplication is 21% higher.
Of course, below that speed the TH can reach 1st, and above it the PG has nothing available except high gear.
Posted by: intergrated j 78

Re: Chevy 250 hp confusion - 08/30/17 11:43 AM

If 3.08 is the kiss of death, then the TH 350- 2.73 gears that I have are the Zombie Appolicapse!!! According to The "Gonlicuator" switching to a 2.74 first gear TH 200 won't help much at the drag strip. Jay
Posted by: Tracker64

Re: Chevy 250 hp confusion - 08/31/17 06:02 AM

What does the "kiss of death" mean? Mine came stock set up this way?
Straight 6, TH350, with 308's posi.
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 08/31/17 05:34 PM

Originally Posted By: intergrated j 78
If 3.08 is the kiss of death, then the TH 350- 2.73 gears that I have are the Zombie Appolicapse!!! According to The "Gonlicuator" switching to a 2.74 first gear TH 200 won't help much at the drag strip. Jay


Glad you finally made it to the conversation....we got another Nova here. wink

Yeah, I keep quoting the "kiss of death" 3.08, but he was just in reference to early Chevy IIs with a Powerglide in comparison to the 3.55 it had initially. I don't think that applies to the TH350 because of the deeper first gear. The question at hand is that TonyPA has a 3.08 Posi on his Nova and is wondering what he should upgrade it to.

For me, my 2.73 is the performance ratio for 3.50 1st Sag, while the 3.08 would be the high perf upgrade.
Posted by: panic

Re: Chevy 250 hp confusion - 09/01/17 06:18 AM

Combination used in many Toyota L6 cars 1990-2000.
1st 2.804:1
2nd 1.531:1
3rd 1.000:1
High .705:1 (overdrive)
Axle 3.769:1
1st X axle = 10.568:1
Overall ratio in high gear = 2.657:1
30 mph per 1,000 RPM (26.6" tire)
Posted by: Lifeguard

Re: Chevy 250 hp confusion - 09/01/17 09:47 AM

Originally Posted By: panic
Combination used in many Toyota L6 cars 1990-2000.
1st 2.804:1
2nd 1.531:1
3rd 1.000:1
High .705:1 (overdrive)
Axle 3.769:1
1st X axle = 10.568:1
Overall ratio in high gear = 2.657:1
30 mph per 1,000 RPM (26.6" tire)


Toyota L6? Auto?
Posted by: panic

Re: Chevy 250 hp confusion - 09/01/17 11:48 AM

Yes, A340E
Posted by: stock49

Re: Chevy 250 hp confusion - 09/02/17 07:38 PM

My S54 equipped I4 MR2 has the following
Gear Ratios:
5th: 0.820
4th: 1.028
3rd: 1.322
2nd: 1.960
1st: 3.285
Final Drive Ratio: 4.176
Yielding a Crawl Ratio = 1st x Final of 13.718

To panic's point the 10x CR is a floor. My NA '92 MR2 left the factory with a 135hp . . . and the Toyota engineers chose a CR approaching 14 . . . in a stick shift.

regards,
stock92
Posted by: TheSilverBuick

Re: Chevy 250 hp confusion - 09/02/17 09:43 PM

My favorite gear to date is the 4.56 gear with a 27" tire and an overdrive. Car feels like a rocketship (though technically still slow) and did well with the overdrive. Even drove to Salt Lake City at 80mph on I-80 at 3200rpm for a hundred miles each way.

Currently have 3.42's and they are pretty decent, but have another set of 4.56's ready to go back in.

My car has a 200-4r in it for an overdrive.

Interestingly enough, a bunch of my friends that run single digits in the 1/4 have been switching to a powerglide with gear vendors on the back and gearing appropriately for the gear vendors to shift going down the track.