Inliners International Forums General Discussion Engines 250 Intake Choice??????

I just bought a '72 K-20 Pickup that had a 454 in it...........Sadly, for all the bragging everyone does about them, it was a real let down IMO. So, I pulled it planning on installing a Cummins 5.9 I was trying to get cheap............Well, guy who has the Cummins thinks its worth a million dollars, so I am going to put one of the inliners I have laying around in it. We ran 250's and 292's on the farm and I really liked them. They would run forever, never quit, and you hardly ever had to put a wrench to them other than for servicing. Anyhow, I got one that we rebuilt and have on the stand. We always ran stock intakes, carbs and exhaust, but I want to do something a bit different on this one. I'd like to run a 4 brl on it. However, I am not 100% sure what intake to use, I've read Offy work well on the low end, and Clifford is for the mid and high end. Now I see Clifford has a twin 4 they are building. I want something that will work well on the low end as well lug the guts out of everything we own, probably the main reason I like the engines I do. I plan on getting headers from Clifford............

While I am at it, I'm going to throw a cam in it to replace the stocker.........Anyone have a favorite that preforms with any of the items listed above. I'll do the porting and polishing on the head at work in the evening.

Not looking to build a 1/4 engine, I want a low end grunt monster. I probably should go 292, but I don't have any at the moment, and this 6 will get replaced by a Diesel sooner or later anyhow.........Its just and inbetweener

If you're looking for low end grunt, Comp cams has one for the 194-292 inline that should work real well. I think they call it a 260H or something like that. What you want in a cam is moderate duration and a lot of lift. Basic rule of thumb with cams is that lift will give you torque, and duration gets you horsepower in the upper rpm range. Don't get too crazy with carburetion, one small 4 bbl should be plenty. The MAIN thing you're going to need is a better exhaust system. Stock Chevy inline exhaust manifolds don't breathe. At all. Nada. You probably should run Tom Langdon's cast iron headers or Clifford headers, or the rest of the things you do aren't going to make a whole lot of difference in absolute power output. Chevy sixes are torque monsters if you let them breathe, but if you don't, they're pretty much meek little lambs as far as power output goes. And either the Offy or Clifford manifolds will work for what you want. Hope this helps some. Might be a good idea to pick up a copy of Leo Santucci's Six Cylinder Power Manual, too. Lots of good info in it.

I planned on using Tom's Cast Iron Headers from the start.......Planned on bending up some extra 2.5" pipe I have from another build which should work well.

I've been told by a few guys that the stock cam preforms the best under 3000K for towing and general use..........Any truth to that? Doesn't some of Comps Hi-Lift Cams require swaping in some different valve springs because the stockers won't handle the lift of those cam's?

I have a Q-Jet off a 307 that I plan on using, My neighbor is really good with them and rebuilt it and it works great.

Based on what I actually am running on my 250 I can say for what you want then use the Offy manifold, the Comp Cams 260H, and the Stovebolt manifolds. I'm using the Clifford Street Rod block hugger style headers but more for the looks.

The Clifford single 4 bbl intake is an excellent mid to top end manifold but doesn't sound what you are looking for. Their dual 4 bbl unit is even further beyond your needs.

I run an Edlebrock 500 carb on the Offy unheated and have no problems summer or winter. Others with the same set up have needed to run heat to the intake so there is no hard and fast rule about it.

The Comp 260H is a great cam for bottom to mid range and besides the grunt it will give it works really well with the intake and exhaust mods you have in mind. You will feel the difference.
Comp recommends using their matching springs but if you look at the specs they are basically a stock replacement. If you are freshening up the head I would recommend just using the new Comp springs instead of shimming and playing with the originals. You can reuse your Chevy pushrods and rockers as long as they are in good shape.

I was hoping I didn't have to run heat.........Seems like an extra headache. I figured Tom's Cast Iron headers would help with that as they would hold some heat in that area unlike bent tubing.

If I go with a new Cam I'll bit for new springs. Easier to replace them at the begining instead of acouple thousand down the road.

Some "food for thought" on the 250-i6 buildup:

I have one of those computer programs for engines, it is pretty well rung out against a lot of dyno data - mostly v8 but as much i6 and i4 as I can find too (always looking for more - )

Since I am planning a 250 and a 292 build right now myself, I found the Langdon iron in Leo S' book and made a guess as to what it will do. Given that I computed the motor you might be building.

When I compute the stock 250 Chev 6 here is what I get - GROSS numbers at the flywheel, 60F air, 29.92 pressure, no exhaust or fan or air cleaner etc ie the "old pre-1972" ratings:

Torq 214 at 2000
Torq 227 at 2600
Power 152 at 3700

Maybe accurate maybe not but now compare to what you might build and how it computes.
I added the Langdon iron, a Clifford 4v and 500cfm carb:
Torq 226 at 2000
Torq 241 at 3100
Power 178 at 4100

My instinct tells me the Comp 260H cam is much better than the stocker - I added this and the computer said:
Torq 206 at 2000
Torq 240 at 3700
Power 207 at 4800
So it lost a little at 2000 but really goes up on the top end. Depends on your use I guess - there is a smaller cam at about 194/204 duration at .050 it might be better for a work truck 250 -

Then I changed from the Clifford 4v to the smaller Offy 4v. This is where I trust the computer the least, but it got me:
Torq 211 at 2000
Torq 241 at 3500
Power 202 at 4700

Gained low, lost high.
Well, short of some dyno data (not much of that in Leo S' book either, very scarce for the Chev 6) those are my best guesses at least something to think about - - -

One more thought on exhaust heat -

The old Ford 4-barrels (maybe others) had a 1" spacer plate right under the carb that ran (hot) water thru it for preheat. This is how I plan to run my unheated Clifford, then again I live in CA. Back in PA I know it gets a bit more brisk in the winter. But this might work - -

Hi, TP, I thought you might like to hear some more input. I built a 194 back in the mid 70's, and the combo I used was an unheated Clifford intake manifold, Sig Erson RV cam with specs very similar to the Comp Cams 260H (mine was 256 degrees duration and .480" lift), screw in rocker studs, valve springs that came with the cam, ditto on lifters, stock pushrods and rockers, Clifford long tube headers, glass packs, a high pressure oil pump, and a Holley 350 cfm 2 bbl carb with an Edelbrock air filter. It put out gobs of torque from 2000 to 5000 rpm. I lived in Los Angeles in those days, so if you're in Houston, you shouldn't need manifold heat too much. The car ran very smoothly, no lumpy idle or hesitation at any rpm range. I think the differences between the Offy and the Clifford intakes is pretty minimal in a street application. I had the Clifford, and as near as I could ever tell, the engine started pulling as soon as I put my foot on the gas. However, I keep hearing that the Offy works better from idle on up, and it probably does. I was also running a 2 barrel carb, so that might make a difference too. I guess what I'm saying is that either one works a lot better than stock. Same with the cam. Stock Chevy inline cams DO work best under 3000 rpm, mostly because they don't have anything left after that. Max rpm is 4000, and there isn't much power after about 3500. Come to think of it, there isn't a whole lot of power UNDER 3000, either, at least not compared to an engine with the modifications you're talking about. An aftermarket cam like the 260H will give you a lot more torque than a stocker will, and do it in all of the rpm ranges. Oops, just noticed that you aren't from Houston, you're from Pennsylvania. That could make a difference in the winter. Keep us posted on your project and let us know how it works out for you.

I'm running a 292 @ .030 over [in my '68 C/10] Crane Cams 260H, 305 V8 [1.86]intake valves, Offy intake, Clifford Research headers, Edelbrock 1404 500 CFM 4Bbl carb. No carb heat - Arizona. Runs real good. On my last engine, it was also a 292 L6 and bored .030 over with a Holley 390 CFM 4 Bbl. I ran it for 25 years. I re-used the intake and headers after minor refurbishing. I'm currently using stock points, but will upgrade later to a Pertronix Ignitor II system.

Thanks Guys. I think I am going with the Clifford 4 brl intake, Run the Q-Jet, and like I said, Cast headers from Tom......

Still up in the air about the Cam...........I might try it stock at first, I want everything on the low end since I like running down there out of habit.

Too bad GM didn't put a cross flow head on these from the start.........They and John Deere must have been in ca-hoots, they didn't start using cross flow heads on their tractors until relitively recently.

Best of Both, this is the cam I was thinking of:

It's from PAW / SSI:
194/204 on 110LSA, .464 .490 lift

With the Clifford 4v and Langton Iron, it gave my computer:
Torq 222 at 2000
Torq 244 at 3400
Power 198 at 4500

Keeps all the low end and adds top end too, and price is right. $50.00

Do you know how much the truck weighs and what trans and rear gear and tires it has? If so I can estimate whether it will actually pull better, down lo and up high.....

Deuce, It is a '71 K-20, I don't know off-hand what it scales at, but I don't recall what they weighed new either. I imagine it might weigh 500-700 more than stock as it has a steel stake body rather than the stock box. I am running 4.10's, with a 4spd. I believe the tires are 265's(16's)......

Will the stock springs work with that Cam? Or do I need to go with different items in that area?

Stock springs will work fine with that cam. Just make sure to go with new ones (I've learned from THAT mistake)! :rolleyes:

-magic mike-

Duece Coupe. What program are you using on your computer to get the dyno numbers? Sounds like a good tool to have.

Martin

My 68 C20, 327, sm465, fleetside, HD duty rack on the bed weighs in 34-35 hundred pounds. Hope that helps.
Larry

TP:
Ok, with a guess of 4300 lb including driver I was able to get my computer to run your "250 computer engine" down the track in the "K-20 computer truck". With the 250 as you described it, I computed 4 different cams:
* Stock 250 Chev
* Comp 240H, 192/200 duration, .455/.455 lift
* PAW/SSI, 194/204 duration, .464/.490 lift
* Comp 260H, 212/212 duration, .489/.489 lift

Here is what I got for gross torq, power, and times:
Stock cam:
Torq 241 at 3100
Power 178 at 4100
For me, in a work truck like it seems you have, the most relevant time was 0-60mph, kinda the classic "street performance time. It was:
13.00 sec, 0-60mph
On the dragstrip I computed times of:
2.38 60ft
11.79 at 58.2 1/8 mile
18.72 at 70.9 1/4 mile

For the Comp 240H "192/200" duration I got:
Torq 243 at 3400
Power 196 at 4500
11.19 sec 0-60, WOW almost 2 sec faster.
2.37
11.57 at 61.3 faster in the 1/8 mile, good
18.32 at 72.3 faster in the 1/4 but so what?

For the PAW/SSI "194/204" duration I got:
Torq 244 at 3400
Power 198 at 4500
11.15 0-60mph
2.37
11.56 at 61.3
18.31 at 72.4
Either the Comp 240H or PAW 194/204 cam are a lot faster than the stocker, and no penalty down low.
Either one looks good in there.

For the Comp 260H "212/212" duration I got:
Torq 240 at 3700
Power 207 at 4800
11.23 0-60mph...SLOWER than the smaller cams....
2.41 60ft - slower.
11.56 at 62.2 - about same 1/8
18.19 at 73.0 - a little faster in the 1/4
That "Big" 260H cam isnt that big but if the truck is this heavy the smaller cams do better. And, they do a lot better than stock.

Well, this computer thing I have is home-built. It is very well wrung-out against dyno and dragstrip data - but mostly for V8's I'll admit. Inline data is harder to come by so take this info for the "free advice" it is, but it is after all computer based, only a dragstrip would tell you for sure.

If I was rebuilding your 250 for that truck, I'd get either the Comp 240H or the PAW/SSI, new lifters, probably new springs (tho I was "shifting" at 4600, pretty low.....)

good luck

Hello Deuce Coupe. Since we're on the subject, could check those three cams against a 3000lb 250 equipped Nova wagon? Thanks.

Martin

Ok. Let me rephrase that: What is the rule of thumb when applying these numbers to vehicle weights? I'd imagine my 0-60, 1/8 mile and 1/4 mile numbers will be lower.

Strummin67,
No rule of thumb but with over 1000lb less weight:
* If it's still a 1-barrel either cam (240h or 260h) would be about the same, my guess

* If it has a 2-v or 4v or 3x1v etc then definitely the 260h will be faster.

Detail about your wagon:
* Trans? (Converter if auto?)
* rear gear?
* Tires?

And engine:
* Carb/intake?
* Head work?
* Compress?
* Exhaust & pipe[s]?

Then I can crunch some numbers. Too bad it is so far to a dragstrip for us, SearsPt or Sac are so far away. There's a Nova NIte at Sac Raceway but it is so far I havent been in a long time

I miss Baylands in Fremont.
Ok. The engine is currently stock but will have a Holley 390 4bbl on an Offy intake.
-Trans is a Borg Warner T5.
-Rear gears are 3:36, tires are 14/205-70
-Will have Langdon's cast manifolds and 2" duals to the rear bumper.
The car is driven daily and sees a mix of city and highway driving. Considering the cost of gas these days mileage is important. I am open to suggestions.
Thanks.

Martin

I did some serching and Engle makes a couple of cams that may work:

http://207.178.130.99/catalog/search_results.php

Boy I haven't heard that word in a while "Baylands" ,I sure miss that place too.

Another thing I've noticed among the cams compared was the dual pattern had a flatter HP and Torque curve than the single pattern(Comp 260H).
Crane's Hydraulic and Powermax cams have the dual pattern with varying durations and lifts in the range we're discussing.
http://www.cranecams.com/index.php?show=...=194-250%20C.I.

Martin

DueceCoupe, I have the dragstrip and engine analizer from Performance Trends. Dad uses there pro version, it requires so much input I stick with the regular version. We have found the trick was to go to the dragstrip and get some good clean passes, then using that information calculate what the engine is really putting out. Once I know the true hp it takes to run a given mph, I can build the engine in the analizer to match those numbers. I then use that engine as baseline and build from there. It works pretty well, I used the baseline engine and sent it to the dragrace analizer, built the truck to match the hp and et. With all the different inputs it easy to get it right on the money.

One thing I have learned, there is no magic cam, intake, or exhaust! To keep it driveable, the low rpm torque is a must. Also, what works on the computer does not always work on the street! Joe

This is true. The car is driven on a daily basis so I won't be going too crazy with the modifications.

Martin

Martin,
Here are some computer results for you.
I agree with JoeH's comments about computer vs street - it's important to be able to predict et's BEFORE you go to the strip, that is one way to build some trust. Usually I like to have a 60ft time to feed the computer - 60ft is very hard to computer-predict - at least for me. After that, if the engine is well-tuned, it is a little more accurate.

Anyway for your 63 Nova (I have 2 of em myself!), and with the same 3 cams/engines as above, I got this for your 63 Nova Wagon, assuming all the 200 lb extra on the rear helps the wagon hook up:

Stock cam:
Torq 241 at 3100
Power 178 at 4100
2.22 60ft
10.19 at 68.6 1/8mile
16.05 at 84.6 1/4mile

Comp 240H:
Torq 243 at 3400
Power 196 at 4500
2.22
10.02 at 71.1
15.72 at 86.4

Comp 260H:
Torq 240 at 3700
Power 207 at 4800
2.27
10.00 at 71.4
15.61 at 87.3

Since you mentioned mileage I'd pick the 240H (or the PAW/SSI one, similear). The 260H might be more fun but computed slower 60ft - a hint about mileage perhaps - but, any of these compared to stock should be a big help.

Hey, drive all the way to Sac Raceway and post a before & after run! That's only 400 miles or so round trip!

Thanks for taking time out to post the numbers Duece Coupe. I really appreciate it.

Martin