Inliners International Forums General Discussion Hi Performance 250 Buildup Advice

Just picked up a 1980 K10 4x4 with the 250 I6, and given the number of oil leaks I'd say it's due for a refresh. Still runs great, but I'm a little anal about oil leaks.

Anyway, since I'm going to be going through it I figured why not build it up a little for a little more power. Not looking for anything crazy as this is going to be a daily driver/weekend wheeler, but wouldn't mind getting up into the 300-350hp range if at all possible. From what I've seen here already I don't think that's to high of an aspiration.

Unfortunately I know absolutely nothing about these engines so hopefully you all can lend a helping hand recommending a combination to meet my power goal while still retaining drive-ability and reliability.

So here we go...

1. Is the bottom end robust enough for this kind of power or am I going to have to get different rods?

2. What's the best option for pistons? Would like to bump it up to somewhere around 9:1 CR, but don't want to have to spend the big bucks on custom forged pistons.

3. Any favored camshafts that everyone agrees on for a good performance street engine? I have Hydroboost brakes so vacuum isn't a huge issue, but I don't want it to have a super lopey idle either. Manual trans so no torque converter issues to worry about, and the axles have 3.42 gears and 31" tires.

4. What 4-barrel intake is favored? Will probably run a Quadra-jet carb for it's off-angle reliability if that helps any.

5. Obviously the heads will need a lot of work, so what all is recommended and is the anyone in particular you guys prefer to send your heads off to?

Any other tips or advice would also be greatly appreciated.

Best place to start getting info besides from the inliners on this forum is definetly Leo Santucci's book " Chevrolet Six Cylinder Performance " You'll find it listed for sale in the Club Stuff section.

The offey would be your better choice for lowend to Mid range power & torque. As for your compression One of two things can be done. (stock 250 has a 8.5-1 compression) You're looking for a small gain in compression,So you can
mill the head and Zero deck the block.Or you can go with a 194 head which will give more then a 9-1
compression.

As for a cam for what your plains are for that truck I would say stay with a Hyd cam and Look for
something in the rpm range from Off idle to around 5500-6000 rpms and no more then a 530 lift This will still make a fairly good daily driver and a weekend wheeler as you put it.

Daul exhaust headers Or Tom Langdons dual cast exhaust will help out with the exhaust flow and help the motor breath better.

As for the head this is were you are going to tie up some bucks.1900-2200. Some shops even more.
The head needs to flow If it don't then all the money you put into the motor (ie cam ,compression,dual exhaust intake carb so on is
not going to give you much If the head does not flow well)

so in order to get this head to flow your looking
at Port work at min. a good 3 angle valve job and
step up the valve size (in. & ex.) you can also have it lump ported.which will also In crease the Cfm flow of the head even on a stock sized valve.

There are only a few shops around that really know anything about our L6 chevy heads. Most all
machine shops work mainly on V8s or now into only the import stuff.

another option to get reliable power is to turbo it. the bottom end will take it fine, if the boost is limited to the 6 lb range. with the right cam and turbo setup you could get 300hp fairly easy. it will take more fab work than most are willing to do. tom

So essentially what you're all telling me is that I'd be much better off just dropping in a small block V8 to get the power I'd want from a cost v. benefit standpoint.

Well, yes. A V-8 is "cheaper" to do. The thing about the inline is torque, which you want on the trail! you don't have to go all out with the lump porting and all that, its nice and it adds power. I used to run a 2.78 rear end in my C10 with a three speed and if i dropped the accelerator at 65 mph, it pushed you back in your seat.

Do you really believe a V8 is cheaper? I have built many 6s for people . Last one was for a 39 Chev coupe and replaced a 305 V8. owner says he gets rubber in alll three gears. Far mor power than the V8 and wonderful gas mileage.
Talk to him if you like. His name is Len and he can be found at "lencol@aol.com" It was a 250 6 cylinder BTW.

oops, i meant to add that its a 250 in my C-10 as well. sorry for the ommission. I probably could have built a V8 with that kind of power cheaper, but where i am at, inline's aren't well recognized for anything! (but it sure is fun to mess with people!)

People see my dual exhaust tips and automatically assume I have a V8. I still love to see their reactions when I raise the hood.

Absolutely, but, as others have mentioned, the inline is "novel" ... small block Chevy's are horribly cliche if you're looking for any kind of style with your power. That's why I'm here. I have a '69 C-10 with the original 250/1-bbl. With regard to power, servicibility, price, etc., it's a no-brainer for me to yank the 6 and drop in a 350. However... I've decided to play with the 6 and keep that aspect of the truck alive. Now... to figure out just _what_ to do with it

A couple of comments. In the initial post, the statement "Still runs great, but I am a little anal about oil leaks", seems to indicate that you are not unhappy with the current performance, but would like more. If that is actually the case, intake, carb, headers and a rv style cam will give you a nice little boost. If you are serious about 300+hp out of a 250 it will cost as you will get into serious head work; 1.2hp per cube is expensive on virtually any motor.

Since changing intakes is mentioned, it must have the early style head. I thought the 80's had an integral cylinder head and if does not, it is likely some major work has been done to it over time.

Also, remember there are costs involved in swapping out the six to a small block or even a big block. You may need different motor mounts, fuel line, throttle linkage, exhaust system, accessory brackets and many more little items which all add up.

I am glad you diecided to go with the six. I seriously question the eightis cheaper theory but hey what do i know. My budget for my rail is $2500 including the motor and I am about two weeks away from being done and still in budget.
A hot 250
6 307 pistons $90 Rings Overhaul kit under $200 on ebay last time i looked. Cam and Lifters about $230 . Z 28 valve springs $40. Machine work 300 to 500 and 200 for stuff we forgot. Power will be way abouve the normal Chev v8 and mileage will also be great.
I wish you all the best. BTW a reworked 292 truck carb showned no restiction on my flowbench at just over 500 intake lift on a stock manifold and a modified head. That engine won Second overall one year in Midstate Vintage Stock Car championship just in case anyone thought I was talking about a slug
D

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D,
Could you explain what you mean by "no restriction"?
I know it has a pretty big venturi.
I plan on running a 292 carb on a 250 to make it look stock.
This engine previously had a 390 Holley 4 bbl on it.
Any tuning tips for the 292 carb would be appreciated.
Maybe this should be a new thread?
Thanks.

mabey price but servicibility? i think inline sixes are the easiest to service. to get real big horsepower it prob will be cheaper but for just a souped up inline i'm not even sold on that. i think parts avilibility and a flooded market of v8 parts is the only advantage.