The Stovebolt Site Forums The Shop Area Engine Shop 235 upgrades

Hey All
So I just dropped off my 1954 235 at the machine shop. He asked if I wanted it to be original or add some modifications like larger pistons and larger cam and so forth. I told him I was just making a driver out of it and not a hot rod and he said I could go either way. He said the larger pistons and cam would give me a little more compression and a little more boost. So i guess what I need to know is what are the advantages and the cons of keeping it original or "beefing" it up? What are your thoughts and what have you done to yours? Thanks!!!!

Hotrodding a stovebolt is sort of like putting lipstick on a pig- - - -unless you've got a deep enough pocket to make some radical (translation" E$$$$PENSIVE) major modifications. There's no real advantage to boring the cylinders out more than what's needed to take the taper wear out of the cylinders. Radical camshaft profiles only add a measurable amount of power at RPM ranges that are seldom seen on the street. It's also necessary to increase the compression to benefit from the kind of power a radical cam provides. At low to midrange RPM, a cam with a lumpy idle actually reduces the power available for street driving and causes major losses of gas mileage in the process. The primary purpose of the mods your "machinist" is suggesting is to increase his cashflow at your expense.

A conservative stock rebuild would be a much better choice unless you have some kind of racing in mind, even if you have to go looking for a different shop. I spent a lot of years building all-out racing engines for round track cars and truck pulls- - - -it's always more fun to go racing on the other guy's money. People were willing to pay me well for engines that won races, and I could have fun doing it without bankrupting myself. Doing race engine stuff on a street machine is stupid squared!
Jerry

You brought up a lot of good points I didn't think about. Especially the decrease in fuel. And at these prices I don't want that! Thanks for the input. He was upfront and did tell me it would cost more to "beef it up" and said it was totally up to me and what I wanted to do. I think keeping it as stock as I can is the way to go. What do you think about using Webber Carbs? I have seen some Youtube videos where they switched out the intake and put on dual webber carbs.

I concur with Jerry on what he said above. The dual Weber carburetors are another story. If you want to improve the carburetion of your engine, please keep the same stock manifolds (both of them) and change your carburetor to a Carter YF model. There are a bunch of reasons it is better than the Rochester. We've slaughtered millions of electrons here discussing it and the correct answer always comes up the same. For your year 235 a YF2100S or a YF2101S would be what you need. The 2100 has a manual choke (not so easy to find now) and the 2101 has an automatic choke (which many of us prefer...Jerry and I are in that auto-choke crowd). As for dual carburetors the best answer I've heard is that you have either one too many or you need one more (like the 3 the Corvette 235 used). Or you might be able to rig up a scheme where 3 motorcycle carburetors could be used. Good luck!

Not sure what year truck you have and what transmission.

IMO, a stock 235 has plenty of usable power and torque and is plenty capable of keeping up with modern traffic.

It’s not more power or carburetor or ignition that they need, it’s more gears to keep the engine in a happy part of the torque curve.

One of the Rube Goldberg projects I've got on the drawing board is running three Keihin side draft carbs from a Harley EVO engine, on some home-brewed individual manifolds. The firing order of the stovebolt engine (1-5-3-6-2-4) means that each of the three intake ports only needs to supply fuel to one cylinder on each intake stroke. The carb for an 80 cubic inch motorcycle engine like a Harley is the right size to meet that volumetric demand, even on the 261 engine which has a little over 43 cubic inches per cylinder. I'm a firm believer in using only one carb whenever possible- - - -getting two or three carbs perfectly matched and synchronized with each other adds just another layer of complexity to deal with. Another option to "improve" the carburetion would be to mill the one barrel flange off a stock manifold and modify the plenum to use a 2G Rochester carb like the 265 and 283 Chevy V8 engine used. That's one of the best engineered, bulletproof carbs GM ever designed. That would best be combined with some internal modifications like the ones I do- - - -increasing the bore and stroke of the 216, 235, and 261 engines to add 30-40 extra cubic inches without getting radical on the camshaft profile or compression ratio. "There's no substitute for cubic inches"- - - - -but that also requires "cubic dollars"!
Jerry

Jerry:

Your mention of a 3 carb system and the firing order got me thinking, which I don't do to well.

Given the 360 degree camshaft cycle of our engines:

The carb feeding cylinders 1 and 2 would get demand at 0 degrees and 240 degrees (240 degrees from #1 cylinder to #2 cylinder, but 120 degrees from cylinder 2 to cylinder 1).

The carb feeding cylinders 3 and 4 would get demand at 120 degrees and 300 degrees (180 degrees from #3 cylinder to #4 cylinder and 180 degrees from cylinder 4 to cylinder 3). This would be the only carb with an "even" demand time between its 2 cylinders.

The carb feeding cylinders 5 and 6 would get demand at 60 degrees and 180 degrees. (120 degrees from #5 cylinder to #6 cylinder, but 240 degrees from cylinder 6 to cylinder 5).

Would this "imbalance" of demand of cylinder pairs 1/2 and 5/6 cause any "weirdness"?

This is all theory to me. I'm sticking with my single Carter YF.

Good questions, Bill. I suspect the “weirdness” is no weirder than the chaotic manifold signal of one carb feeding 6 cylinders. But I’d love to hear a more educated opinion.

The three carb idea isn’t totally unique. Plenty of aftemarket manifolds and the corvette side draft thing.

But each of them being on a truly separate manifolds is a different animal. I’ve seen some antique “homemade” versions of what Jerry is describing. Mostly downdraft versions and who knows what carb they were running.

The 4 stroke cycle is 720 degrees- - - -not 360. Intake- - - -180. Compression- - - -180. Power- - - -180. Exhaust - - - -180. Add them up, you get 720 degrees. On a 6 cylinder engine, there's a 120 degree separation between intake strokes. With a firing order of 1-5-3-6-2-4 and three intake ports, only one cylinder is drawing air through the carburetor on any intake stroke. The carb only needs to be calibrated to supply an air/fuel mixture equal to 1/6 of the engine displacement. On a 235 that's 39 cubic inches, and since it's impossible to get 100% volumetric efficiency on anything but a highly modified racing engine, the practical limit is around 90% or a little less. That's around 35 cubic inches on a 235- - - -and that's at wide open throttle and around 3K RPM.

The laws of physics aren't "suggestions". The most common mistake virtually all hotrodders make is "too much cam" and "too much carburetor"!
Jerry

As I said above, I was referring to the 360 degree CAM timing. I learned about 4 stroke ( suck, push, pop, fooey ) from my Dad when I was 8.

I love hopping up my stovebolt motors and I have been doing it since I was a teenager, so for some 47 years. The stovebolt motor is as susceptible to performance improvements just like any other motor. More compression, more flow, more cam, more carb, more power. But, its relative. Getting 10 percent more power out of a 400 cubic inch motor is not the same as getting 10 percent more power out of a 235 chevy. The gains are relative to the motor.

Dual carbs are for those who want a little more power and like to tinker because dual carbs require a little tinkering.

So a lot of the aftermarket intakes for the early 235 and 216 motors were set up for small base carter carbs. Why? Because the motors came with those carbs. If you were going to install a dual intake on one of those motors, you only had to buy the intake and one carb.

The later motors, for example 56-63, came with Rochester B and BC carbs so the aftermarket intakes for those motors were set up for the wider base of the later Rochester so again, you only had to buy the intake and one carb to do the swap.

The problem, those carbs were in fact really too big to work well in a dual or triple set up. In fact, to get them to run right, you have to do a lot of work to the various circuits. But the other issue, those carbs have problems inherent in the design, like the pesky freezing power piston, that is in addition to any issues with the dual carb set up

The Carter YFs are good carbs, but the W-1s are better I think because they have a mechanical power system that can be adjusted, where the YFs have a vacuum/mechanical system that cannot be easily adjusted and thus in a dual set up, YFs will run rich, just like the Rochesters.

One solution is to use a pair of Holly Weber 5200 progressive two bbl that came on the Ford Pinto. I like the versions for the 1974 Pinto. They run pretty good right out of the box. Small primaries, larger secondaries. Almost perfect.

So you are thinking, why not just a single 5200 on a stock manifold with an adapter? Does not really run all that well, a single 5200 is just a little two small.

So, if you want to do a few things to improve your motor, have the block surfaced nice and flat. Have the head surfaced nice and flat. Bore the block to the next available oversize so you have nice straight well machined bores. If you want a cam that breathes just a little better and you are using mechanical lifter, get a cam for a 261 chevy truck. Can't find one, send your cam to Schneider Racing Cams in San Diego and have it reground. Cantrell, the owner, likely has even better grinds that get you a little more power (remember its relative) then the 261 cam. Otherwise, have your cam reground to stock specifications.

Want to do some other things? If you are reusing a stock distributor, have it properly rebuilt. You would be surprised at how much better the motor will start and run when its working as it should rather than as a 60 year old distributor that has never been serviced. Have the rocker arm assembly properly rebuilt (Rocker Arms Unlimited in California. They are the only game in town). Not cheap, but the motor will run way better and way quieter with the valves properly adjusted and the rocker arms staying where they should be when operating. They can also re-machine your lifters so you have a nice fresh machined lifter face for your nice fresh reground cam.

I learned (and taught) the 4 stroke cycle as

Suck
Squeeze
Bang
Blow

LOL!
Jerry

Where is the best place to find the Carter YF ? I think the auto choke sounds like a plus as well

One has only to look at the intake port configuration of the cylinder head to understand Jerry's and Jon G's comment that 2 carbs is either 1 too many or 1 too few.

Two carbs may add "eye candy" to the uninformed, but unless done perfectly (selection, calibration, synchronization, etc.) two carbs may actually LOSE power!

If three carbs are used, they must be matched, and the three carbs should each be smaller than the stock single barrel carb. Carter type W-0's would be my choice; others may prefer Autolite 1100's, (Ford 144 CID engines) or Rochester type H (Corvair). Others (hi Jerry) might prefer motorcycle carbs. I have some personal experience with using slide Mikuni's on a performance engine; after 1/2 a season, they were totally worn out!

With all due respect to both Jerry and Jon G. (the old cliche about agree to disagree), at age 78 I am not old enough to need an automatic choke and I really prefer the performance of the manual choke. While the choice is yours, DON'T use the auto choke IF you modify the engine; you won't be happy with stalling at stop signs

Use of a "big" camshaft moves the engine efficiency curve to the right. More power at higher RPM's, less power at lower RPM's; and higher fuel useage across the entire RPM range. I have modified a number of non-Chevy engines for street use, and ALL of them exhibited these characteristics.

Jon

I've picked up a few YFs on Ebay- - - - -"rebuildable cores" at pretty reasonable prices. The carb for an AMC/Jeep 232 cubic inch inline six is calibrated about right for a 235 Chevy, and other than a bit of tweaking of the throttle linkage it's a simple thing to adapt it to a stovebolt engine. Those carbs are also about 25-30 years newer than the mid-1950's carbs, so they're less likely to be worn out to the point they're not rebuildable. RUN- - - -do not walk away from the new, offshore-made replicas of the Carter carbs. Junk right out of the box!

For instance:
www.ebay.com/itm/186709751802?

Jerry

Jerry - the off-shore imitations (they are NOT replicas) of the Carter carbs are actually VERY useful.......................IF you have a strong right arm, and a rabbit problem in your garden!

Paraphrasing a comment I have seen you make in the past: "these are NOT a solution to a problem that doesn't exist".

Jon

PM sent.

Jon

Good memory Jon- - - - -I believe my favorite version of that phrase (stole it from my Dad)- - - -"A solution desperately looking for a nonexistent problem!" I really miss him!
Jerry