The Stovebolt Site Forums The Shop Area Engine Shop 235 with dual carb- does it make a difference?

I have a freshly rebuilt 1954 235 with twin one barrel carburators and dual exhaust. It also has a modern HEI distributor. It is coupled to a saginaw two ring transmission with a Hurst shifter. I am thinking of installing it into my 47 3/4 ton. Does anyone know how much more horsepower this adds? Is it really worth it?

other then looking good I am not so sure that they would add that much more speed,, some may not agree,what vehicle do you have it in now? regards..Fred

I think the main thing that hurts the 235 is not having as much torque as the big inch stovebolts. Having two carbs is not going to really do anything for low end torque, but will help in the upper band horsepower and midrange. I have a 235 in my 3/4 ton and it seems barely adequate. I cannot believe you could actually load 3/4 of a ton into the bed and have that stovebolt handle it. I mean it will, as long as you don't ask it to go very fast.

I really don't like my weak 235 very much. It is reliable but at my altitude, it can't get out of its own way. I'm going to try a turbo to see if that improves it any. If not, I'll join the bandwagon and go V8. But that's my opinion. Others may differ.

I had the exact same set-up in my '51 1/2t PU...it was estimated that with a 3.55 rear we made in excess of 150HP.

If the motor in your '47 is original, it's a 216.
Came with Dip 'n Splash oiling, and babbited bearings.

The upgrade to a 1954 235 would give you ~10% more cubic inches, full oil pressure, and "modern" insert-style bearings.

The block looks the same, so you keep "originality points"; it's definitely a "period authentic" swap.

The dual carbs are a nice touch; but won't add as much as the '47 216 to '54 235 bump alone will get ya.

GO FOR IT.

And btw, rear end ratio does NOT affect how much horsepower your engine makes....

Cheers,
mark.
'51 KY 3100

Here are some things that WILL make a difference in both torque and HP.

Re-cam
raise compression
polish and port the head (biggest gains here)
go to 2 bbl twin carbs or small 4bbl
HEI
split manifold or Fenton

These are not cheap power gains but unless $ are the big issue you can get substantial power from an I-6. Mine makes 180HP. So your engine already has most of the goodies, just pop the head and start grinding and you'll be surprised. There are cams for grunt and cams for speed so pick what you want just don't expect more than about 5K RPM unless it's professionally balanced, etc.

I just recently purchased my 235 from a guy who decided to go ahead and put a 350 v8 in his 54 truck. My 47 3/4 ton already has a 350 sitting in it, but it was put in very sloppy(by previous owner) and has never been finished. That is why I am considering this 235. I have a new old stock 1959 235 head that I was told made greater compression. Can it be placed on my 54 325 to increase hp? Will it interfere with valve/piston clearance?

I seriously doubt it would cause valve clearance problems. You can take a lot off those heads, up to .125 on some. I had mine milled .060 without problems.

What does a 3:55 rear have to do with horsepower? How do you estmate horsepower?

I know your question is about the 235. But here is an article on the 261 that gives numbers.
http://www.selectric.org/55chevy/soup.html
Kind of hard to read but it states that,

Stock 261 = 77 BHP at 2000 rpm
and torque= 201 pounds-feet at 2000 rpm.

With dual exhaust alone = 80 BHP at 2000 rpm
and torque of 210 at 2000 rpm.

With dual exhaust and a 2x1 with two Strombergs
= 89.3 BHP at 2000 rpm
and torque of 223 BHP at 2000 rpm.

What this does show is just by adding dual exhaust with free flowing mufflers and a 2x1 intake with Strombergs gave the 261 motor a

16% gain in HP at the low end of 2000 rpm and a
11% gain in torque at the low end of 2000 rpm.

And at 4000 rpm the gain was 21.5% in BHP over stock.
And an increase of 23% in torque over stock.

These are documented dyno numbers on the 261.
For a 235 I would think the percent numbers would be pretty close to the same numbers as the 261, give or take a small percent.

So dual exhaust with dual carburetors DOES add hp AND torque to these old Chevy sixes. A good 20% more at 4000 rpm.

It's not going to snap your neck, but only you can judge "Is it worth it" ??

For me the answer was "YES" it was for me.

A 3.55 rear has to do improved performance...all the HP in the world is worth anything unless you can get it to the road without blowing up the engine!. HP is estimated using the dyno testing/readings from the various vendors. (i.e. Fenton,Offenhauser, Mallory, exhaust system vendors).

You have not said a thing about the 3:55 rearend.The gear ratio will improve performance,but it will not change the horsepower of an engine.If you have a vehicle dynoed to tell you the horsepower at the drive wheels it will be a horsepower rating ,not an estimated horsepower.In other words,I took Bubba for a ride in my truck with 3:55 gears,and he said man that feels like 150 HP.Now thats an estimate.

You have not said a thing about the 3:55 rearend.The gear ratio will improve performance,but it will not change the horsepower of an engine.If you have a vehicle dynoed to tell you the horsepower at the drive wheels it will be a horsepower rating ,not an estimated horsepower.In other words,I took Bubba for a ride in my truck with 3:55 gears,and he said man that feels like 150 HP.Now thats an estimate.

Your both right actually. The best way to "estimate HP" IMO is to buy one of the many computer dyno programs and get it that way.

Engine dyno ratings are different from rear wheel ratings obviously just as percieved "performance" is more a seat of the pants thing or against a timer.

So what is the disagreemnt, gentlemen? And frankly, if your happy with the thing, who cares?

I'm working on my first restoration of a 51 1/2 ton Chevy that already has the swap to a 54 235. In the above discussions I saw no mention of the electrical systems. Is that an issue? My truck has the original 6V (including the original wiring, which presents an entirely new set of problems), and I was wondering if it pays to put in a 12V or one of those 12V start/6v running systems?? Any thoughts about that?

By the way, the tech talk you guys throw around is unbelieveable to me of little knowledge. This stuff is right on point and beats having to buy all those truck and car mags in hopes of finding an article or two that just might pertain to your vintage truck. Thanks for that.

The six volt system will work fine, but is less tolerant of lack of maintenance and poor connections. It is also harder to find six volt accessories such as stereos.

One would have to define performance in order to claim that a 3.55 rear end will increase performance over a 4.11. Everything else being equal, the 4.11 would be both quicker and faster in a quarter mile and in stock condition COULD even have a higher top speed because the 3.55 gears don't allow it to reach an effective point on the power curve. The 3.55s will make the driver more comfortable due to less engine noise and the engine may be happier at lower RPMs on the highway, but is that performance?

made 378 hp. dyno after modifying a engine suppose to be stock 350hp. carb,ign,cam,exhaust,rockers, etc.
Rear wheel hp. only 265. dont know how you can use mfg specs to determine hp.

A good dual carb set-up is one of the greatest and least expensive horsepower gains you can make on a 235. That was proven by Mechanics Illustrated 50 years ago. They took an early full pressure 235 and did all kinds of experiments each time testing on the dyno and the 1/4 mile. The single greatest gain was the dual carb set-up with the addition of a third carb adding a few more horses at higher rpm's. However, at that time they did not have anything like a 390 Holley and a nice Clifford manifold to go with it. There is a real bone of contention in certain circles in this area. Some will claim the multi-carb set-up always works better on an inline and others will favor the modern 4 barrell for its simplicity and ease of tuning. Me, I think three carbs with little chrome filters is worth about a gazillion cool points and will perform at least as well as the 4 barrell if not better.

Boo

I can see why the multi-carb set up is favored. It is probably because of more equal fuel distribution to the cylinders. When you use the Clifford intake with a 4 bbl Holley, the center cylinders will always run richer than the outer cylinders, because of the log-style intake manifold. With the log style, positioning the carbs so that the distribution to the cylinders is more equal is going to have a more positive effect, I would think.

If someone would build an intake that would raise the Holley 4 bbl up, therefore giving it more equal length runners, then maybe that would put the 4 bbl ahead. Look at the V8 in performance applications. Today you can get more performance out of a single 4 bbl than multiple carburetion BECAUSE of the advances in intake design. In the 60's, if you wanted more power, the multiple carb concept gave it to you. That's not the case anymore.
I wish someone would design some better intake manifolds for these Stovebolt engines, because I think there certainly would be a market for it.

53MoneyPit, I see you're not far from me. Come nicer weather, I'd really like to come down to Elizabeth in my truck and check out your truck. I'd like you to take me for a drive so I can see how an updated Stovebolt performs. What say you?

OK Dad, we'll do that come spring.

I doubt eldebrock or others will make a new manifold... lets be honest, most people will swap or build a v-8 before and I-6. But with some ingenutiy you could fab one up yourself. I don't think it would be very hard if your handy with a welder

I don't think it'd be that easy. I saw one made with a roots blower on top, and it was novel, but I don't think it would be very easy to fabricate.

I'd probably start with mandrel-bent header primary pipes and weld them to a common plenum above the valve cover. On top of this plenum would mount a 4 bbl carburetor. It would be an interesting experiment and would probably run reasonably well. But frankly, I think I'd get a lot more power out of a turbo using the stock intake because it would be force fed.

MoneyPit, I'll contact you in the spring. I'd really like to see your truck, and I'm anxious to see how a built stovebolt runs.
Thanks.

I think both Joe H. and Tony P. here have built their own 6-cyl. intakes. Maybe if they see this, they'll have something to add.

So why can't one just compare the specs of a stock truck motor versus the specs from the 54 vette 235 with 3 side drafts, split exhaust, and a higher lift cam (same as 261?) ???

Well, in one of my Vette books, it mentions that the triple carb 235 in the '53 Corvette is good for 150 hp. So still not a very strong engine, even with all those carbs. However, in a lightweight Corvette, it probably didn't feel too bad.