Inliners International Forums General Discussion Hi Performance Performance Enhancements for a Chevy 250

I'm a 15 year old and I got my first car a little over a month ago. It has a chevy 250 in it. I've been thinking about putting in a few different performance upgrades but I want to run it by some people who know more than me. Here they are...

Intake - http://www.summitracing.com/parts/OFY-5416/?rtype=7
4 Barrel Carb - Some Holley Carb. Probably a 390cfm. You guys think it could take any more cfm if I used a performance cam (the next thing on this list?)
Performance Cam - Either a 268 or a 280. Which one do you guys think I should use?
Headers - http://www.summitracing.com/parts/BIG-11510FLT/

And a couple other ideas I had were... a 292 crank because I heard somewhere that you could mod the block to use a 292 crank in a 250 block (what would that involve?). Maybe a 194 head for higher compression. and installing lump ports (what would that do?)

Any of your ideas or helpful hints would be great. Thanks

Putting a 292 crank in a 250, while possible, is rather complex for a first engine. You would be better off with an offenhauser 4bbl intake, the 268 cam, and some shorty headers with 2 1/4" dual exhaust. That would be a nice running little 250 that wouldn't break the bank.

That was probably going to be my plan but I would probably have 2.5" dual exhaust. Any idea what type of HP that would produce? stock is 160HP so what would that be? 250HP? or am I shooting for the stars? What would make the 292 crank that complex?

Check out the Clifford Engineering web site. Clifford at one time had pistons maybe a kit to put a 292 crank in a 250. The block and cam has to be clearanced internally for the rods.

IF the exhaust pipe is too large you won't create enough back pressure for the headers to flow properly.

Do you Leo Santucci's "Power Manual"? You can find it on the left under "Club Stuff".

Larry

Check out the Clifford Engineering web site. Clifford at one time had pistons maybe a kit to put a 292 crank in a 250. The block and cam has to be clearanced internally for the rods, for starters.

IF the exhaust pipe is too large you won't create enough back pressure for the headers to flow properly.

Do you Leo Santucci's "Power Manual"? You can find it on the left under "Club Stuff".

Larry

Going to be dyno testing a 250 next weekend! Look up the post and start reading.

The 292 crank will require alot of bank breaking parts. Building the 250 will put a smile on your face. Or you could really put a 292 under the hood. Tom

You didn't tell us what the 250 is in. The headers are for a pickup so thats probably what you have. I think Tom's dyno tests will show us some interesting numbers. Personally I think your choices so far are fine, Offey manifold, 390 4bbl, 268 cam, flowmtech headers. I'd use the stock head with 1.84 or 1.94 intake and 1.60 exhaust valves. The big inakes will have to be unshrouded. I'd remove the bosses and install lumps. I'd probably get a set of forged V8 pistons and use them and head shaving to get the compression from 9 to 9.5 to 1. Don't use the stock fiber cam gear. I'd use stock GM HEI ignition maybe with an MSD 6A. Get Leo Santuci's book and prep the block well. This is about as cheap and easy as it gets and it would run well. There is a lot of good information on this site in old posts. It is sometimes hard to find, but it is there. What trans and rear end do you plan to run? Welcome to Inliners. Join our club we need the young blood! Beater

I was looking into putting in a 4 speed muncie and having to cut a hole into the floorpan. Right now I believe I have a Saginaw 3 in the tree. I have a low geared non-posi in there right now. I think the gearing is just below a 2 which doesn't seem right but aw well. I might eventually get a posi if I have the extra money laying around. I don't know if I said this before but I have a 69 Buick Special Deluxe and looking at it now, those headers won't work. I'm looking into joining the club but I need some money first! :-)

I think you would be better suited to either build a 250 or a 292. The 292 crank in the 250 block will work, but as has been already mentioned, creates some issues that really aren't beneficial for dependability and longevity without spending a lot of money. The 292 dyno testing that was done previously yielded right at 300 HP and up to 330 Ft. lbs. of torque, with simple basic components. So getting 250 HP out of a 250 shouldn't be that difficult either. As tlowe mentioned, those dyno tests start next week, so keep watching for updates as it progresses. Welcome to Inliners.

Putting a 292 crank into the 250 has been known to lead grown men to drink; out of the question for a 15 year old....we'd like you to be around for a while so stick with building the 250, you'll be surprised....welcome to Inliners.......fats

Alright haha. I'm helping my dad building up a 68 GS 400 and I'm just looking for a fun engine with a lot of umph. I would also like to give him a run for his money but am I just dreaming there?

If you do have a Saganaw 3 speed and it has over drive don't let it get away! The OD can be put on a Saganaw 4 speed and you'll love it. Get a set of short cast headers from Tom Langdon or Patrick's. My son got his '54 Stude wagon when he was 15. You and your dad will have fun. Beater

No it doesn't have OD. I just has 4 shifting points in the column: R, 1, 2, and 3. Would it be hard to put different gears in there (or is it even possible)? Could I convert that transmission (that is in the column right now) into a floor shifter? What would be the differences between a 3speed Saginaw w/ OD vs. a 4 speed Muncie?

Floor shift conversions have been used for years and are available for 3 and 4 speeds. The OD on the Saginaw is contained in a special tail housing on some 3 speeds. It is activated by an electric solenoid and a governor system. That three speed uses the same case as the Saginaw 4 speed so the OD can be put on the 4 speed. That gives you 5 speeds or 8 if you want to play with it. All of the older standard transmissions had a 1 to 1 ratio in high gear whether 3 or 4 speed. The 4 speed usually just makes the ratios closer between low and high and allows you to use the engines power band more efficiently. They can help turn a quicker 1/4 mile if you can shift. There were some close ratio 3 speeds that were pretty quick. The ODs are usually about .70 to 1 which either reduces engine RPMs by 30 percent at a given speed or raises speed by 30 percent at a given RPM. In the late 60s the Saginaw 3 and 4 speeds were all the same length even if the 3 speed was OD. They will bolt into your car. The 3 speed OD would use your column linkage. It might even be possible to shift a 4 speed from the tree if you shifted reverse separately.(sort of a pain) Some people lay much praise on Muncie 4 speeds. They are lighter, more expensive, and somewhat stronger. No trans will stand up to constant abuse. I ran a hot Olds in front of an early Ford drive train and eventually learned to drive it. It was a hand full. I hope this helps. I think it's mostly true. Beater

If you get a Muncie ,,,I would not suggest a close ratio (2.20 1st gear ) one especially if you have 2. somthing rear end ratio.

You would absolutely hate the initial take off in first gear.

I did not like it even w/4.10 gears.

Better off installing a T-5 tranny.


MBHD

Actually now that I've been looking a little bit on Craigslist, I was looking into getting a 4 speed saginaw w/ a Hurst shifter for about $200. I was also wondering... Since the final gear would be a 1:1 on the 3 speed and 4 speed, then how could I make my car more efficient? When my parents are driving their cars on the highway in their '09 cars, their RPM's are barely above idle (like 1100 or something). Now, I don't have a tac, but I'm guessing I'm running like 3000 RPM going 65 down the highway and my redline is 4500. Is this normal? I mean I understand that automatics work differently but it seems that this would make all manual cars DRINK gas. I mean going on a 65mph highway for like 2 hours would use up a tank. I'm already using an INCREDIBLY low gear... and a 4 speed wouldn't help so how can I make that any better? Thanks

Like I was saying a T-5 trans would work nice.

There are different ratios & they are all overdrive 5th gear.

What rear end ratio do you have 4.11?


MBHD

You are about right on your RPM at 65 mph. I'd say maybe even a little higher 3300, depending on tire size. If we are right about the RPM you have a 4.10 rear axle.

You have two choices change the rear axle or install an over drive. As Hank says a T-5 is a good choice. There are a lot of folks using them and they are fairly common. It might not be the best choice if you are going to get a big engine and bang gears or haul heavy loads. Then the choices near a bit NV4500, MY6 (A833) are a couple, unless you want to consider an automatic.

Larry

As Hank said pick a trans with the right ratio. You need to know for sure what your rear end ratio is. If you are lucky it will be on a tag on one of the differential cover bolts. If not it may be stamped somewhere on the center housing or one of the axle housings. It will for sure be stamped on the ring gear. $200 isn't bad for a Saginaw 4 speed with a Hurst shifter if they are in good shape. I like the 3.11 first gear for my pickup with 3.55 rear end and 30" tires. My 270 GMC likes to run a 3000 RPMs but I like for to run closer to 2000. With OD I'm at or near 2000 between 70 &75 mph. Here are a couple of tables you can play with to help you sort things out. And again as Hank keeps saying there is the whole Borg T5 tranny swap. That may be easy in your case if you have room for the long tail shaft and don't need the short S10 tail shaft so the shifter clears your seat. But there are some changes. The saginaw should bolt right in. Beater

trans ratios

Gear ratio & tire size

Well I really want to use either a saginaw or muncie tbh. I also DEFINITELY want to keep it a manual. I locked up 1 tire and turned the other and the drive shaft turned just over 2 times so it is geared INCREDIBLY low. I'm confused, is OD an installable gear or is it an extra gear in the way it is built or what? Why isn't it just called a 5 speed? I've found a working saginaw 4 speed and a working muncie 4 speed w/ hurst shifters for about $250 (each). Could I use the same bellhousing for all these trannys? And just a general question about I-6s... would they be in any way comparable to a v-8. Like I said earlier in this thread, I want to give my dad a run for his money with his suped up V-8 so I just was wondering what I was expecting to get out of all of these upgrades. Thanks

Double check how to determine the rear axle ratio. The way in which you did it requires that you multiply the number of turns by 2. I have 63 C20 with a 4.10 rear axle at 65 mph I'm turning 3300 RPM. If your ears are correct your guess of about 3000 RPM is correct, you have the rear axle ratio 4.10.

You can use the same bellhousing with those transmissions.

Larry

If you have 4.10s you will need over drive. That leaves out the Muncie. The Saginaw is the old school approach. The T5 is newer. A T5 may be the best way for you to go because the parts are easier to find. The solenoid that fits the Saginaw is hard to find and expensive. Maybe half the cost of a T5. There are some posts on this site about using then behind 250s. It takes some work but it isn't too hard. Here is some Borg OD info. Beater
Borg OD

I don't know if you ever said what kind of car your 3 speed trans is in, but most of the GM compacts (Chevy Nova, Olds Omega, Buick Skylark, and Pontiac Ventura) all used 3.08:1 rear end gears with six cylinder engines, except for the station wagons, which had 3.36:1 gears. I think one of the first things you should get is a tach, so you'll really know what your rpm at a given speed is, and the second thing is to get a copy of Leo Santucci's book and read it before you start buying parts.

GM pickups did use lower rear end ratios than cars did, so if you have a truck, it may have a 4.10:1 rear end. I have a '68 Mustang with a 3.50:1 rear end in it, and it turns 3500 rpm at 65 mph according to the tach. One of these days it'll get a 5-speed. Back to your car, though, one of the main things involved in building a hot rod, or just modifying what you've already got (which is pretty much what you're doing) is knowing what you're starting with and figuring out what you want to do with it and how to make everything work together so it's fun to drive after you get finished with it.

You would need to lock one tire & turn the other wheel one full revolution,then multiply how many times the driveshaft turned by 2.
So,if you counted the driveshaft turns a little over 1 & 1/2 turns,you would multiply that by 2 which will be 3.08s

If you want any advantage & give your dad a run for his money,you'll need to gear all the gearing advantage as you can get. A T-5 trans will give you better take off than any muncie.

There are some Saganaws w/a low first gear, but no overdrive.

You should be able to find a used T-5 in junkyards,or Craigslist or friends or?

Any other trans are going to cost you some $$$ like a doug nash 5 speed (think they have a new name now?)
T-56 6 speed .50 OD? which would need an efi to use 6th gear unless you had like 4:88's
Just off the top of my head,so not too accurate,but I think close enough?

MBHD

alright guys. Sorry I haven't replied. I spent 7.5 hours yesterday under my car right after school:-). I'm replacing the clutch right now. Got the driveshaft and tranny off yesterday. Got the bellhousing and pressure plate/clutch off today. Gonna start reassembly tomorrow (and hopefully finish). Back to the task at hand...
I'll probably end up going with a muncie because I've heard those are more reliable than saginaws and to make up for the high revs, I'll probably get a lower rear end gear because I do think that I have a 4.10. But what should I be expecting out of this? I mean I know I already asked this but if I do everything short of a super/turbo charger then what kind of HP/torque and I looking at with new intake, 4 barrel carb, headers, and high performance cam (and lifters, springs, etc.). Is there anything else I can do really? I've heard about installing lumps but didn't understand what they do. Also what would be the effect of installing a 194,230, or 292 head? I know you guys are going to tell me to go get santucci's book but just ballpark it for me plz ;-). Thanks

The 250 was factory rated at about 155 hp. With the addition of simple bolt on parts, 4 bbl intake and headers expect about 175 hp. Put in a small performance cam and get about 200hp. Perform headwork, Bigger valves, porting, bolt in lumps and get about225-230hp. Put in a big cam and you will see 275-300 hp.

No "194" high compression heads for me. They will not work well with larger valves( shrouded valves)

I am about to dyno a 250 with just these kinds of parts to test performance gains. It all starts this weekend. Tom

You'll make 200-250 HP @ the crank.

Using a properly set-up 194 head you will gain 1 point of compression & make more torque.
Dont let anyone tell you different.

If you go w/a bigger camshaft your cylinder pressure will drop & therefore making your engine sluggish.

So if you are going to install a bigger cam, you always want to increase the compression ,so you will @ least have the same cranking compression as before & the simple way to do this, is to install a 194 cyl head.

Two cents thrown

MBHD

what would installing a 194 head involve? Does it bolt right on? So like remove -> replace gasket -> put on new head? I also don't get how the cam or head would change compression. I thought the compression is determined by the amount of travel on the crank. And wouldn't the smaller ports on the 194 head actually decrease performance or cause the engine to drown by having the gas liquidize before entering the cylinder? Inversely, by that logic, wouldn't putting on a 292 head add displacement?

Displacement is not measured by volume in the cylinder and head chamber, rather it is the measure of the amount of volume that is 'displaced' by the piston as the it moves the min height to max height in the cylinder, i.e. stroke x ((bore/2)^2 x Pi) = displacement for an ind cylinder. By putting on a smaller chamber head it means that there is a smaller volume to be compressed by the stroke, thusly, increasing compression and conversely the compression will be lower with a larger chamber head.
Displacement and compression are two completely different measures.

I believe that before you make head and compression decisions that you need to determine you cam lift & duration, valve spring and valve decision.

Good luck. It's nice to see a kid 'dare to be different' and stick with the inline.

the 250's were reated anything from 140-155 hp. As for compression pistons come in different dome(top) shapes a dished piston will have less compression then that of a flat top or what is called a POP-up/domed piston.The Ports on the 194 head are the same as 230,250,292 heads The difference is the underside/Compression chamber or Quench area of the head.
The lift and duration of anyone givin cam also exfects your compression.Installing a lump kit to your head helps improves the short turn raduis issue the stock head has.By improving this
it does increase the air flow of the head. The 194 can give up to
a 10-1 compression and with the proper head work can flow as well
as any other head ,And you don't have to mill a boat load off it
to get the same compression or the use of a pop-up. A flat top
piston can give you better performance over a dished piston,But it will not give you more compression with out milling alot off any other head 230,250,292.A pop-up can give you much more compression & performance. But the spark has to pass over the dome,You can also fire slot the domes to help the spark get to the compressed fuel.
So if your after a small gain in compression with the stock dished piston, A properly done 194 head can give you just that.

if you are going to install a bigger cam, you always want to increase the compression ,so you will @ least have the same cranking compression as before.

This is very important.
However, it's frequently just not possible to completely recover the lost low-speed power by raising the static CR, unless you increase the cranking pressure quite a bit.
Just an exaggerated example: a 250 with 9:1 static CR and conservative 55° intake valve closing (at 14.7 psi ATM) will show about 154 psi on a gauge, producing perhaps 245 ft/lbs. of torque at 1,000 RPM (47 hp).
If the intake closing is delayed to 75° (quite a bit), the pressure falls to about 125, only 169 ft/lbs. of torque at 1,000 RPM .
Raising the static CR to 10.6:1 brings it back up to 154 psi, so that's fixed, right?
Nope.
The same cranking pressure is acting on a "smaller" cylinder due to the shorter effective stroke at the new closing point, and only making 204 ft/lbs., still much less than the stock engine.
To get the same torque at 1,000 RPM, the static CR would need to rise to 12.4:1, with 188 psi gauge pressure.

Yes, it's complicated

Overall, what I was trying to say was, just dont install a bigger camshaft & not do anything else.

Many times people just look @ installing a bigger camshaft & do not realize that the bottom end will most likely suffer a bit.

They will read a camshaft estimated HP you could get from it & not even think about you will loose by gaining more top end HP.

As I am reading what the guy is looking to do & not tear open the bottom end & change pistons or do other things as to raise the compression ratio for more power. He seams to be interested in @ least changing the cyl head. ,,Correct?

Changing the cylinder head is the most practicle way of raising the compression & easiest IMO.

Any good cyl head shop should be able to know how to & where to unshroud the intake valves in the small chamber head to get it to flow good.

I was just suggesting a way to somewhat recoup your cyl pressure loss do to a larger camshaft installed. I did not say you will recoupe all your losses.

He wants to whip his dads ride,, I say do what ever seems possible w/in a budget,while using his stock shortblock.

Gearing is another choice & in his sights,that is why I suggested a T-5 to have an advantage over a Muncie gearing wise.

If his dad is using a 400 CI engine & a Muncie 4 speed, what advantage does the little 6 w/a Muncie have over a 400 CI engine,,,nothing really,, other than the L6 is lighter.

So basically what I am thinging this guy is on a budget & wants to think & do things to his car to whip up on those V-8 thingys.

MBHD

Alright. My dad has a 68 GS 400 that we're rebuilding to a little over the stage 1 performance package. So nice big cam, headers, quadrajet, and it's probably going to be bored a little over since its old. Not sure if he's turning the crank. Probably like 390HP or 400HP when we're done. He's going to be using a turbo 400 transmission so that puts him at a slight disadvantage because it's an automatic.

I finally finished putting the clutch, tranny, and driveshaft back in today. Went driving for like 10 minutes and I was actually kind of disappointed at how slowly it accelerates in 3rd. I know it would probably perform better if I had a 4 speed because of the wider range of gears, I could use the higher RPM's more. I want it to be fun and not like... "i'll get up to speed eventually..." and "where is this thing called 'torque'?". I want it to be "punch you in your seat" torque. I don't really see what else I can do short of a turbo/supercharger besides what I said before: cam, intake, carb, headers, and maybe the head. If I got a 194 head, would I need premium fuel? Not sure what the point of this post was but it was just my ideas and a question or 2...

If you are looking for that kind of "seat of the pants" acceleration and sensation, you might consider a 292 instead of a 250. All of the dyno tests that Tlowe did, showed that from just about 2000 RPM on up, with all the combos tested, the engine never fell below 300 ft. lbs. of torque until way on up in the RPM's.

You could use regular gas,depends on your camshaft selection w/the raised compression.

Right now,you probably have between 8.2 - 8.5:1 compression w/a stock head now.

A TH400 trans is not really a disadvantage over a 4 speed.
More consistant,1/4 mile runs,easier to drive,etc.

Yeh,the 3 speed hurts/kills the pull when you shift into 3rd gear,rpms drop too much,I know ,I had the same trans when I bought my car.
There are different ways to help your 250 run better, but you will need to sacrifice something most times to gain something.

Like if you want more torque out of it,raise the compression,(might need to run 89 octane) more top end,camshaft,keeping the engine closer in the torque band,5 speed.

292 would be nice,if you want a torquey stump puller.But,how much does a 292 weigh over a 250? Adding weight also slows down your acceleration.

MBHD

"where is this thing called 'torque'?". I want it to be "punch you in your seat" torque

You're re-reading the same page again, looking for something that's not there.
Torque = displacement (and some compression thrown in). All that speed equipment does is raise the RPM at which the torque occurs.
250 vs. 400: guess which one wins?

Panic is right, theres no replacement, for displacement!

While boost will make more power, enough boost to beat your pop's GS (if it is "warmed up" at all in the engine department) will take a dedicated build of the engine (boost specific) and drivetrain to make them all survive.

Neat goal to be sure, but you'll have to work that way in increments (ie, lighten the car, better gear and posi, beter trans, solidly built longblock) if it's to be any kind of "budget" build. (yeah, I hated that advice too when I was your age )

alright guys... looks like my final consensus of your answers and a few of my own ideas are...
-4 speed (because I didn't want to get an automatic like someone suggested)
-probably a posi and I'll probably get it a little lower than a 4.10 maybe 3.83 or 3.53.
-intake and 4 barrel
-headers
-cam it up
-194 head (I'll probably need some help on what to do to the head once I get it)
-HEI distributor

So thanks guys. I'm sorry if I wasn't clear. This is going to be a daily driver and I'm not looking to DESTROY my dad. I just prefer not to run like an 18 and have him run like a high 10 or something in the quarter. I understand that "there's no replacement for displacement" (which is ironically is a saying that I first heard from my dad a few weeks ago). I'll hopefully make some vids of my progress on youtube. I've already made a vid of my car if you guys want to see it http://www.youtube.com/snowman4839 . That was when it was bone stock but I've put some rally wheels on it (because they just happened to be really convenient for me to buy) and my dad helped my adjust the timing. I've also replaced the clutch like I said. I don't want to replace the 250 with the 292 because it's a matching numbers engine and I prefer to keep it that way. Thanks for your help guys and the warm welcome into the inlining world :-)

because it's a matching numbers engine

You're already modifying everything else, and I have yet to see someone refuse to buy something nice "because the numbers don't match".