The Stovebolt Site Forums The Shop Area Engine Shop How much HP can be made from Chevy 235??

Hey guys, I just brought home a 235 out of a '54 pickup. The engine is mostly disassembled already and needs to be rebuilt. I bought it to eventually replace the stock 216 in my '52 pickup. My plans for the rebuild include split headers, dual carbs and a mild cam. Other than these upgrades, what else have you done to increase the HP of these engines? I don't expect to achieve V8 hp, just wondering what a realistic goal will be after rebuilding? Thanks for your input.

The head is probably the biggest restriction.
Heres a parts outfit
http://stoveboltengineco.com/catalog/store/

Here's another source.

With regards to the head, look for a relatively common 56-63 235 head, with a casting code of 3836848.

If you are going to spend money on reworking a head, do it on an "848" head. I plan to just get a machine shop "head job" done on a "848" head for my 1954 235 that I will eventually rebuild.

My guess on hp is that with an "848" head, dual exhausts, 261 cam, and any bigger carburetion, you could get 150 hp or maybe a litle more.

My appoach to carburetion on my 235 is now "keep it simple". I'll be looking for a 1-barrel 248 GMC Zenith carb with a variable jet. It may not look cool, but it will be simple and reliable and give a fuel-feed equal to the needs of the engine. I'll find out if that is too much carb.

I assume the '848' head is a better flowing head over mine. When the time comes I will look for one. Thanks for the tips, the number I had in my head was 150-175hp which isn't too bad considering my stock 216 only makes 86hp I believe.

They all flow the same it's that the 848 head has the smallest combustion chamber. The same thing can be accomplished by milling any other head casting however valve train geometry becomes polluted. The Corvette 235 was rated at 150 hp so you're expectations are reasonable and I can also say with some certainty that the documented modifications made to the stovebolt head back in the days before the flow bench did not always improve flow as expected so don't overdo it.

What is an acceptable limit for milling the head down? Also do you think it would benefit to port/polish the intake and exhaust ports? And of course a good valve job would be in order....

i have said this before in another post that people here didnt want to believe but if you have your block bore and honed with a torque plate you will see a big hp gain for doing this,and the other thing that might be better to do instead of milling your head down is to zero deck your block,mock up your new pistons in the bore and see how much they are in the hole, if they are .020 down mill the block .020,then you would have a zero deck block,much better for the burn, you can mill the head some too if need be.

Besides boring up .060 safely you can mill the head quite a bit but I'd stop at as little as it takes to get it totally level.

As for the head I doubt there is any stock factory head that would not benefit form some good porting relief and polishing.
Get yourself a copy of the Chevrolet Inline Six-Cylinder Power Manual by Leo Santucci. It is written for the next and last generation of OHV GM inlines but there is much to learn from it regardless. The ignition change to electronic is crucial in my opinion. Helps starting immensly (spell check please) as well as overall performance. The Desktop Dyno (yeah,..I know) claims mine has 174 HP which I greatly doubt but it does run nicely and has power. These old girls will run a higher RPM than most of the folks here like to hear but back in the 50's we'd run the guts out of 216's and 235's with almost no internal damage. The price to fix one has become so expensive that most guys are now afraid to run them. I say let'r go. It's only iron so have the fun.

Zero decking increases compression in the same way milling the head does but valve train geometry remains undisturbed so I have to agree that's the best place to start. Torque plate boring is also a magic ingredient IMO but the scarcity/expense of them is what likely would make a rebuilder downplay the benefit. It's a good idea to get in the ports with a die grinder and knock down the barnacles/casting flash but major alteration or resizing will have little benefit. Flow is mostly generated by the area close to the valve seat so a good 3 angle valve job will give the most bang per dollar of flow improvement.

your not going to get a lot of air flow from a 235 head,just look at it and you'll know why,but the best cam to use would be a cam with a lift of .212-.215 @ .050 lift, if you over cam it you will lose your bottom end but the top end would be better, but with all the gears and really how fast do you want to go? low end torque and mid range is best,maybe a cam that is no more than 260 duration and set the springs up with 85-95lbs.closed,balance it,do a nice valve job and call it good,new cam and new lifter would be the best,regrinds are not as good because your taking materal from the base circle.

Thanks guys for your input. Now to finish disassembly and off to the machine shop. Anyone know a reputable builder in the north Georgia area familiar with these Chevy 6's??

a cam with a lift of .212-.215 @ .050 lift

Where do I get one of those?

The difference between milling the head and milling the block is a little convoluted.
Neither one moves any valve train components directly, and no changes or calculations are needed, unless either one makes the pushrod too long to adjust properly.
How are they different?
A good sized mill on the head chews off the intake seats, and the re-cut seats sink the valve into the throat and make the intake valve stem longer - which changes its relationship with its rocker arm. The cure, 3 options:
1. use a bigger valve with the stem height matched to the original height. This may lead to the valve crashing the piston @ TDC, especially with a bigger cam.
2. after the new valve job is done, you need a shim for each of the 6 rocker stands. The thickness is the difference between the stock intake stem height and the new height (probably less than the full mill distance). However: this also makes the exhaust valve too short to contact its rocker correctly. If the difference is less than .030" I'd ignore it. If it's .060", add a lash cap to the exhaust valves only.
3. replace the seat with an insert (I don't like this, but it's possible).

Resurrecting an old one here --

I've seen several recommend to mill the heads (or deck the block) to increase compression, then sink the valves to maintain clearance between valve and piston at TDC. Clifford Performance says only the intakes need to be sunk -- maybe there's naturally more clearance at TDC on the exhausts.

Anyway, it looks to me like sinking the valves would only make a poorly flowing head worse. Can the flat-top pistons be fly cut to provide the needed valve clearance? We're not talking about a lot here. Pistons are typically .045" in the hole on stock form, so even bringing them to zero deck (a big change in CR) wouldn't require much material being removed.

Thoughts as to why this wouldn't work, or why sinking the valves is more commonly recommended?

Thanks for sharing your experience.

What would your quench be on the head? I would probably just change the Pistons to gain some compression, maybe a thinner head gasket and stay within the .039 range. Tweek on the heads and then choose a cam.

I'm told that the FS7782 261 gasket is .040" compressed.
Without decking the block, pistons .045" in the hole, you're at .085".
I don't know if you can really call that 'quench', LOL.
Well outside the design guidelines of a 'quench motor'.

Depending on the details of your build, pistons .020" in the hole would put you right around 9:1. (261, .020" over, with an 848 head)

So, thoughts on flycutting valve reliefs into pistons rather than sinking the intake valves?

Flycutting the pistons is the logical solution, but nobody applies much logic to stovebolt modifications- - - -they just parrot the same old advice that's been around for 70 years. Back then, the pistons were cast iron, and flycutting them was not an option for most shade tree wrench jockeys building their hot rod on a shoestring budget. It was simpler to have a machine shop mill the head and sink the intake valve the same distance as the milling job. I remember reading that advice in a Hot Rod Magazine article in the mid-1950's when the 2nd.-generation 235 was a relatively new engine, and the 1957 "high compression" head was something only the rich kids could afford!
Jerry

And then you have to worry about how to contain that extra 7 horsepower. Keep the dogs and children inside the house!

That's why the guys who wanted to go fast built flathead Ford V8's!

Jerry

I replaced my 235 with a 250. A set of twin headers came with the 250. My thinking was that looks kool and the headers will give me another HP or two. Big problem thoo. The headers interfered with the Steering Gear Box. Had to remove them and revert to the original Exhaust manifold. Moral of this story. Check your measurments, spacing and clearance on the Split Header before you lay out the bucks for them. 235 and 250 have ALMOST identical manifolds.

What brand headers?I have Fentons installed on my 235 without interfering with anything.

http://www.jalopyjournal.com/forum/threads/the-ultimate-235-hop-up-thread.552360/
More information.

Hello,

Can you tell me if you were able to purchase a dual exhaust system for the Fenton headers? I have been on a waiting list from Patrick's in AZ for quite a while to purchase however he has been out of stock for quit a while. My truck is not running yet and it would be difficult to egg it to a shop to have the exhaust made.

Thanks,

Terrence