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Old 02-06-2020, 03:24 AM   #1
BlouDon
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235 Compression ratio upgrade?

According to the 1959 Chevrolet Owners manual I have, the 235 has a compression ratio of 8.25.

What would be the easiest way to upgrade that to around 9?
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
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Old 02-06-2020, 04:28 AM   #2
mongocanfly
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Re: 235 Compression ratio upgrade?

Shaving the head will bump the compression slightly...
Not sure what piston the 235 has , but if its dished , a flat top piston would bump it up...
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Old 02-06-2020, 05:12 AM   #3
BlouDon
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Re: 235 Compression ratio upgrade?

Quote:
Originally Posted by mongocanfly View Post
Shaving the head will bump the compression slightly...
Would be nice to know how much it can be shaved and how much that would up the CR?
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
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Old 02-06-2020, 09:37 AM   #4
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Re: 235 Compression ratio upgrade?

You may want to try the stove bolt website. They are dedicated to the inline 6 motors. This site is really good but most of the engine mod guys are v8. There are a few into the 250 i6 motors but I haven't seen much as far as 235 mod people here. You may want to research the chevy blue flame Corvette motors as they were the hottest 235s.
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Old 02-06-2020, 01:56 PM   #5
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Re: 235 Compression ratio upgrade?

This is a stovebolt thread from 2005 scroll down to the post by Tony.

Basically having the block decked so that the pistons are flush with the surface which has to be done on a bare block and taking about .060 off the surface of the head.
https://www.stovebolt.com/ubbthreads...t&Number=51003

Valve to piston top clearance is critical when you start milling the head.

Guys in the states look for the "848" (last numbers in the casting number) heads as they are said to perform. Those are 58/62 heads
More stovebolt chatter on that here https://www.stovebolt.com/ubbthreads...s/11773/2.html

I doubt the performance gain would be worth the added expense though. Great if you are hunting for a head because you need one but maybe not a better solution than using what you have now.
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Old 02-07-2020, 02:40 AM   #6
BlouDon
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Re: 235 Compression ratio upgrade?

A lot needs to happen before I get this, IF I get to this. was just wondering. I suspect (hope / wish) that the truck will be just fine with the new diff.
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
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Old 02-07-2020, 11:31 PM   #7
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Re: 235 Compression ratio upgrade?

The 235 doesn't flow enough air to really benefit from bumping the compression up. There''s a number of issues associated with milling the head. One being the intake valve is basically flush to the bottom of the head. The valve seat would need to be machined and recessed. You may also run into some piston and valve clearance issues by doing this. Has the block and head already been machined? Chances are on a 60+ year old engine, someone has been inside it. Exhaust ports on cylinder 2&3, 4&5 are siamesed, so you run the risk of excess heat by bumping up compression. If you're swapping heads, you need to make sure your block has the correct oil orifice for your rocker assembly also.

Anyhow, sorry about being a negative Nancy. Just sharing what I've learned over the years.

Anyway, most guys just clean up the barnacles in the exhaust ports, install a 261 cam. Install split exhaust and a dual intake and drive away happy.
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Old 02-08-2020, 12:07 AM   #8
Bimus
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Re: 235 Compression ratio upgrade?

Mechanical lifters help .I had one 235 rebuilt and they put hydraulic lifters in and big difference low power .
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Old 02-08-2020, 10:32 AM   #9
whitedog76
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Re: 235 Compression ratio upgrade?

The 235 is expensive to work on and finding quality parts, even here in the states, is an issue. If you have one that runs, you're better off just leaving it alone. I've actually had 3 different 235's come through my garage. I got frustrated and decided a drivetrain swap is a better alternative. Looking at your other posts, it looks like you're not afraid to tear into things. You may come to a point of asking yourself, "why didn't I just install a small block?"
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Old 02-08-2020, 11:38 AM   #10
BlouDon
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Re: 235 Compression ratio upgrade?

Sounds like it is indeed better to just leave it alone and drop a V8 in there if the 235 really proves inadequate.
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
Jensen Interceptor '74: Mopar 440 / 4L60e & '73 std
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Old 02-08-2020, 12:02 PM   #11
lv2tri2
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Re: 235 Compression ratio upgrade?

I split the exhaust and added a dual intake and two carters, a definite improvement in performance. I loved the sound.
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Old 02-08-2020, 01:34 PM   #12
BlouDon
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Re: 235 Compression ratio upgrade?

Quote:
Originally Posted by lv2tri2 View Post
I split the exhaust and added a dual intake and two carters, a definite improvement in performance. I loved the sound.
No pics, it did not happen :-)
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
Jensen Interceptor '74: Mopar 440 / 4L60e & '73 std
Jaguar: '72 E-type Coupe V12 & '80 XJS
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Old 02-08-2020, 08:05 PM   #13
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Re: 235 Compression ratio upgrade?

My 235 started and ran pretty good when i got it, it had an 848 head on it. Head had no paint on it so assume it had been off and had a valve job? Who knows. Did the Fenton dual carb and Fenton dual exhaust. I used Holly 5210 progressive carbs from Vegas. Havnt had it on the road yet but it starts, runs and sounds good. Pics dont want to work.
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Old 02-09-2020, 08:04 PM   #14
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Re: 235 Compression ratio upgrade?

Back in 54 & 55 Chevrolet built the hottest factory 235 by installing what would later become the stock 261 cam, triple 1bbl carbs (one for each siamesed 2 cyl's), the "848" head and a dual exhaust. They advertised it at 150 HP. There are hotter aftermarket cams on the market now and one can add two Ford Escort 2bbl progressive carbs and probably match that HP output but you'll be hard pressed to squeeze out any more.
As mentioned above shaving the head too much upsets the valve geometry and increases the likelyhood of piston interference and there's no good way to port the head to gain any more flow. Knowledgeable engine builders often refer to the Stovebolt engine (216,235 & 261) as glorified tractor engines ....
Changing the block to a 261, reusing the "848" head, going with dual intake and exhaust may get you over 150HP but not by much.
If you want to run 65 - 70 change out the rear gears to 3:55, kits are readily available.
Changing to a V8 ain't no piece of cake but many here will help you spend your money if you want to go that route, LOL.
All that said I run a "hopped up" 0.060" over 235 in my 49 Chevy 3100 with stock drivetrain and I still smile when I take it out cruising back roads and highways but I leave the interstates to the more modern vehicles. It'll do 55 - 60 all day long and I've hit real close to 80 but only twice after I broke it in, I didn't want to blow it up after just building it LOL.
Rebuild the engine to spec's, get a hotter cam, improve the carbueration and exhaust and change out you rear gears, you'll have a pretty good performer.
Good luck.
A couple pics of my 235 setup.
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Old 02-09-2020, 10:04 PM   #15
lv2tri2
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Re: 235 Compression ratio upgrade?

Quote:
Originally Posted by BlouDon View Post
No pics, it did not happen :-)
Might have had a picture then but 1966 was awhile back.
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Old 02-10-2020, 07:01 AM   #16
BlouDon
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Re: 235 Compression ratio upgrade?

Would the intake from a late 250 fit the 235?

I'm toying with the idea of grafting the double or tripple SU side draft setup from a 4.2L Jag six onto the 250 manifold and bolting this lot to the 235. That should solve most carb issues surely? (want to keep all 235 parts in storage.)

I'm not interested in HP. I'm only interested in maximizing torque, idle up to 2500 RPM.
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Chev: '70 C10 350 V8 / 700R4 & '59 Apache
Jensen Interceptor '74: Mopar 440 / 4L60e & '73 std
Jaguar: '72 E-type Coupe V12 & '80 XJS
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Old 02-10-2020, 01:10 PM   #17
Volfandt
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Re: 235 Compression ratio upgrade?

Quote:
Originally Posted by BlouDon View Post
Would the intake from a late 250 fit the 235?

I'm toying with the idea of grafting the double or tripple SU side draft setup from a 4.2L Jag six onto the 250 manifold and bolting this lot to the 235. That should solve most carb issues surely? (want to keep all 235 parts in storage.)

I'm not interested in HP. I'm only interested in maximizing torque, idle up to 2500 RPM.
The 230/250/292 series engines are longer than the Stovebolt series engines and they are not direct bolt on. It's a shame since the 230/250/292 intakes and heads flow much better.

Try and find a 54/55 Vette 3 carb intake and it's matching dual exhaust manifold but be advised they aren't cheap. And they won't do you any good without changing to a 261 or hotter cam.

You could also try adapting 2 of those SU side drafts to a 235 dual carb intake with some kind of 90 degree adapter but without a cam upgrade you'll be wasteing gas.

The 261 engine is the torque monster of the Stovebolt series engines and it would be a direct bolt-in. You may have to swap the front motor mount off of the 235 to it but even in it's stock form you'll feel the difference over a 235.
Chevy only put them in 1 ton and bigger trucks/buses from the factory. That would be your best bet to get more torque.

Changing over to a 250 or 292 is almost as much work as going with a V8 so keep that in mind. Course one can build either that'll challenge a SBC.

You won't gain much, if anything by upping the carb size over the stock carb on a stock 235. You can increase the main jet in a stock carb and do better if your exhaust flows better than stock otherwise adding more or bigger carb's is just eye candy on a stock 235.

I'm no expert and haven't stayed in a Holiday Inn in years (joke) but in my non-professional experience there isn't much one can do to a 235 to improve it's performance that already hasn't been done by the Chevy Engr's on the 54/55 Blue Flame 235.

Good luck
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