The Stovebolt Site Forums The Shop Area Engine Shop 235 specs?

Hi folks. I'm new since discovering this forum the other day. I am also a new owner of an old truck, and it has a Chevy 235 straight 6. (The original had a screwdriver stuck in the piston that tore it all up!)

Not being very familiar with the 235, other than its reputation for reliability, I have a few questions I wonder if anyone might either know or could recommend a good book I could buy, or both.

First, what is the bore and stroke of a 235? And I read something about a 6.6:1 compression ratio, correct? As far as the carb goes, it's just a single barrel, and seems to almost limit engine rpm to a little over 3000 rpm. It's also rich. What type of carb is that, and are parts still available for it?
I've been eyeing some new intake ideas and I see that Offenhauser sells 2 and 3 carb intakes for the 235, but they're the same type of carb (that I don't know of a source for). Does anyone make an intake to accept either a modern Holley 2 barrel or small 4 barrel?

Thanks!!!

Ohh Ohh I get to answer first!

235's production life spanned from the mid-40s to 1962. It went through several major design changes over those years. Up till '53 the engine was a "splash lube" and didnt have full oil pressure lube to rod bearings. In '53 Chevy improved the 235 to aluminum pistons, full pressure lube with insert bearings, higher compression ratio (7.5:1) and a different head to produce a whopping 115 HP. The 55-62 engines are most desireable, having better water and oil pumps, better main bearings, higher compression, options for solid or hyd lift cams, 12 volt electricals and up to 140 HP.

The 235's major claim to fame is it was the first powerplant for the corvette. Yes its true! 53-54 vettes had a 235 with a special cam, manifolds and carbs. V8s replaced it for 55-later vettes.

Common carbs were the Rochester B models and Carter W-1. Clifford Performance makes manifolds that will accept a 2 or 4 bbl carb. Offy makes (made?) manifolds that will accept 2 or 3 of the 1bbl carbs. The 2 1bbl models are best for the street. The 3 one bbls are for show, as a street motor doesnt need them and you get into firewall clearance issues with the rear carb. There are other manifolds that will accept the holley/weber progressive 2 bbl carb(s)

Fenton split headers or having your stock manifold split are options for dual exhaust. Smittys steel wool packed mufflers are the authentic 50s hotrod muffler to use with these setups.

Clifford and Howard and others make performance cams for these engines. Solid lifter grinds are most popular. I could go on and on, but these are the high points.

Here's my setup:

'60 235 block zero-decked and bored .060", cast flattop pistons
Total Seal moly file fit rings
reconditioned stock rods
Crank cut .010"/.010" Balanced
melling std pressure oil pump
'60 pump pickup w/ '57 baffled pan.
clevite 77 rod and main bearings
Howard M4F cam, solid lifters
New rocker assys (NAPA)
recurved stock dist with petronix ignition
12 volt starter and 168 tooth ring gear
Manley street-flow valves w/hardened seats in '54 235 head, shaved .040" to raise compression.
comp dual springs and retainers, viton seals
fenton headers, smitty mufflers
clifford water heat intake, 390 CFM holley 4bbl carb.
3 speed column manual tranny, 3.55 gears.
short shaft water pump, electric pusher fan.
Makes about 165 HP at 4500 RPM. Cruises at 3,000. Keep in mind this is an obsolete engine design that dates to the 216 engine from the '30s-40s. Low RPM torque monsters. Not high winding, and siamesed head ports and heavy rotating assy keep it from being a real performance engine. But they're a lot of fun, and different. The dual exhaust has a wierd sounding exhaust note. My setup does a great job dragging a '54 Bel-Air around.

good luck

chip

Check with Tom Langdon at the Stovebolt Engine Company. www.stoveboltengineco.com I think he even sells the Holley and Webber 2bbl carbs that you would interested as well as several other little goodies. Other guys like Patrick's Antique Cars and Jim Carter's are good guys to look at when considering modifications to your intake. I also agree with Chip, in that, Clifford's make great stuff as well. I think they manufacture a lot of there own products. They seem to have a lot of experience with these engines and any will be glad to talk to you over the phone. Good luck and welcome to the Stovebolt!

Great help guys, thanks!
Chip, the 145 horsepower of your engine and 4500 rpm limit is very impressive to me. I realize that it is not the hp that gets this truck moving, it's all that torque. A typical 4 cylinder motor might make that level of power, yes, but would be a dog in these trucks because they don't have the torque. It's the torque that makes these engines so impressive.

Between my two hotrods, the Firebird with it's torque monster 465 is by far more satisfying to drive. The Corvette's 427 may make more horsepower, but it's a peaky engine that only feels ideal at very high rpms that break every traffic law. For the street, I'm convinced torque is the unsung hero...also exactly what you want in a truck.

Well, you might consider this controversial, but since I think I have the later 235 (by virtue of my 30-35 psi oil pressure), I think it might live with a low boost small turbocharger. I have 3 or 4 various Garrett T03's on the shelf in my garage from my experiments with the Shelby Dodge turbo cars a decade ago. With a 6 cylinder driving it, it might be strong from 2000 to 4000 rpm. I'd have to keep the boost down around 6 psi to avoid melting a piston, since I'm sure these aren't forged. But I'm wondering, are these cranks forged like the early Chevy small blocks were?

The turbo would be experimental only. And it would be fairly easy, except for the plumbing to and from the intercooler. And if I end up disappointed by the power returns, I could reverse it and go back to natural aspiration. I'd only have to move the alternator (12V converted), and there's plenty of room.
It's either that, or I do like you did Chip and rebuild the entire motor with higher compression and new cam. This might be another method to have my Stovebolt and enjoy it too.

I would prefer a Holley 2 bbl since I'm so familiar with tuning a Holley. With a turbo, it'd have to be sealed in a box, or...it might give me enough performance improvement by itself.

Are there any good books that can tell me more about the engine itself? Such as combustion chamber cc's, valve sizes, stock cam profiles, what's forged or cast, stroke and rod length, questions like that?

Thanks, Tony

Okay, I looked up Langdon's website and Clifford performance and looks like good sites. Clifford had two intake options I'd be interested in. Their 2/4 bbl intake looks good, but is too large to work with stock exhaust manifold. However, Langdon's Stovebolt site sells Fenton cast iron headers that convert this to a dual exhaust and look great. Clifford's Q&A page seems to indicate that their 2/4 bbl intake requires at least 350 cfm to work well, but yet they sell a 2 bbl adapter which is under 300 cfm if you use the typical 2 bbl. So I have a question in to clarify this discrepancy.

Cliffords also sells a very inexpensive 2bbl adapter to fit on a stock 1bbl intake. Yes, this is quite a funnel, but the thought of a modern Holley 2bbl is attractive enough to try that out first before I go too radical with a turbocharger.
The funnel wouldn't help hp, but torque doesn't care much, plus the improved air/fuel ratio alone would greatly help how this motor runs.

Cool stuff. Thanks! Keep the suggestions coming, I'm learning a lot.

A turbo on these low speed poor breathing engine is a great idea,and not too difficult as you say.I set up a Holley 2300 on a stock intake on a 261 Chevy(larger truck version of the 235)The carb is around 280 cfm,was used on a IHC 266 V-8 engine.I opened up the top of the manifold,made a mounting adapter from a piece of resin board,drilled and tapped holes for mounting, made up a linkage.There more details,but if you mess with turbo, this would be a piece of cake costing pocket change.Oh, a 2 bbl is rated different than a 4bbl,so the 280 cfm I used is marketed as 350 cfm.I previously had installed a 2-1/2 inch single pipe on the stock exhaust with a cheap turbo muffler.
The engine has far better rsponse and power and actually gets slightly better fuel mileage.I tried a 2 bbl on a funnel adapter,wasn't worth the effort.
The stock Rochester is a sorry carb even compared to other single barrels of the day, a Carter yf or Holly 1904 single barrel is an improvement.
140 hp rating was on a factory dyno with no assesories and everything absolutely perfect, real word power at less than 4000 rpm is around 110 hp

So you were able to use the 4bbl intake with a stock exhaust? You didn't have any clearance problems?

I'm glad to get the feedback on the funnel adapter. It does look like trying to force the air/fuel mixture to do acrobatics to get to the cylinders, with the outer cylinders probably running lean. So it would make sense that the engine would run more efficiently with the more modern intake and carb on it.

I guess I could go either with a Holley 2bbl or a 4bbl if it's the little 390. The 4bbl would be way overkill for the low rpm 235, but might be okay with a turbo. The 2bbl I think would be ideal for either situation.

It is tempting to swap cams at least. 50 years of technology could make a really huge difference. I wish I could feel how one of these engines feel in a truck with carb, exhaust and cam mods.

Dad, a picture is worth a thousand words Holley on modified stock intake
My other truck is a 37 Chevy with a modified 261,hotter cam, Fenton headers, 390 Holley on a Clifford intake.I did a lot of experimentation with carbs,seems these engines don't need a lot of carburetion for most tuning applications.A small 4 bbl will work on a 235 ,just make sure the secondary opening rate is delayed as long as possible.More carb may feel better, but the stop watch says differently.

Okay. If it's a vacuum secondary carb, the engine will pull what it needs and may not ever open the secondaries fully. The spring tension can be tuned to where it's operating as a 2bbl almost all the time and only start opening the secondaries when the engine's wide open climbing a hill or something.

I like your picture. It does show the manifold fitting just fine over the stock exhaust manifold. How much better would you say your engine runs with that set up compared to original? And how much improvement would you say the Fenton headers added on your '37? I'd like to add the Fentons, but I should probably use the stock exhaust if I'm thinking about turbocharging, that would make the conversion simpler.

I did something similar on my old oil bath filter. I cleaned it out and got a top-breather K&N type 10" filter. On the Holley, I'll probably use the rest of the 10" round filter also.
Thanks.

Okay, since I am completely sold on the Holley / Weber 5200 carb, I have to weigh in here. I currently use a carb and adapter I bought from Langdon's Stovebolt in my 250 inline. (This engine has 323K on it.) I did not notice much improvement with performance or mileage, but this engine is WORN OUT. What I did notice is that cold starts, operating at low speeds, all around drivability, taking off from a stoplight; it all got better by a whole bunch. In cold weather it starts with the bump of a key like a chevy ought to, and you can drive off as soon as the oil pressure comes up ( about 30 seconds.) The water heated choke is absolutely awesome. So anyway, I am going to rebuild this old war horse next month using a bit lumpier cam, and a little work on the ports, et. I'm not going to try to turn a 4000 pound truck into a hot rod. I just want to put a bit more scoot in the giddy-up. When I do the rebuild I am going to work on both manifolds. I am going to split the exhaust, and open up the top of the intake to set up a better mount for the carb, and eliminate the adapter. I am convinced that for a mildly built or stock 235 or 250 the Holley/Weber 5200 is a VERY good choice. I'll keep ya posted.

Boo Radley

Dad, the 261 in my 37 with the Fentons, cam and more carb was something I built that way from the start.But compared to the "stock" 261 in my 51 truck, the 37 is quite a bit more lively,and revs easily to over 4500 rpm, something the stock 261 won't do even with the 2 bbl carb.Of course the 37 weighs 400 lbs less, but both have the same gear ratios.
I would say the 2300 Holley 2bbl added maybe 10 hp? It idles better too starts instantly hot or cold.
Boo, the 5200 is an excellent carb, but it's my opinion it's a bit too small for other than a stock engine.Holley rates all 5200 at 280 cfm,but that's a 2 bbl rating. To compare a 2 bbl to a 4 bbl,you must use a factor of 1.4 more or less.So the 5200 becomes 200 cfm it you look at it like a 4bbl.Anyhoo,the best way to know is to try it out on that hotter engine,if it works for you ,good enough.I'm thinking a Rochester flows 70 percent of the 5200. On some engines,the small primary throttle of the 5200 kills a little power at part throttle.I know a guy who modified the linkage so both throats open together, he claimed it was a good improvement with no loss in economy.