The Stovebolt Site Forums The Shop Area Engine Shop 235 modifications

Need some input...

I'm planning to add fenton headers and duel exhaust using 2 1/4" pipes on my '60 Chevy with a stock 235.

Also I'm either adding an adapter on the intake manifold to bolt on a 2 barrel Carter carb -or- I'm going to change the intake manifold altogether in order to add the new carb.

My question is, how much more HP and torque may I expect with this setup? I'm not looking for a lot but 15 to 20 would be nice.

Thanks.

Anybody........Anybody????

I would not expect any increase that high in either HP or Torque. The I6 cylinder head really doesn't breathe that well without some modifications. You would get more of what you want with a cam change.

Yes, 15-20 hp would be nice but Drew is correct.

Here is a 1955 article about the larger 261.

I'm curious about what intake you are thinking of that will accept a 2bbl carb?

I think 2 in. pipes are plenty & easier to work with.

In case anyone is interested, here is a 1-barrel to 2-barrel adapter. It does not raise the height of the carb very much if you do not use an insulator with it.

I've read the single barrel on the stock manifold performs better
than a 2 barrel with the adapter. I think carbking has discussed this a few times. A search will turn up lot's of info.

Steve,

Change to dual exhausts and perhaps the situation changes? Also, it depends on the 2-barrel that you would be using.

I'm sure those are factors, Tim. I am not an authority on the subject, I just remember the carbking commenting on that a few times.

A two-barrel carb on a two-barrel to one barrel adapter might COST you 15~20 HP; it certainly won't gain you anyyhing (other than looks).

I am unaware of a good two-barrel intake, but if one exists together with the headers, you might gain 8~10 percent on a stock engine.

15~20 HP would be doable if you also do a cam change and some head work.

Jon.

So, if I replace the single exhaust ( 1 3/4" pipe ) with duel exhaust ( 2 1/4" pipe) this will not gain me any HP or torque?

This engine has about 40,000 on a rebuild and is running great, I just don't think it's time to crack the engine open to rebuild and add a new cam YET!! In the future, yes. So I'm looking for bolt on stuff to enhance the HP and torque a little bit.

Are there any other things I could do to increase the HP/torque?

Thanks.

Anybody!!

Sounds like you are better off finding a 261 and building it on the side with all the tricks. A stock 235 puts out close to 130 hp and about 190 lbs of torque. You could build a mild 261 to put out about 190 hp, but it will cost.

Iron Clad;
The 261 is a great engine and if I had a 235 and a 261 and was looking to install an engine in a new project then I'd certainly pick the 261. However, you stated you have a good, low mileage 235 and are looking for some bolt-on HP - right? Keep in mind that a stock 261 was rated at 150 hp while a "stock" Corvette 235 put out 155 hp. As far as I know the Corvette got that hp with carburation and dual exhaust and without the benefit of an "848" head.

You asked about dual exhaust - in the great McGurk article that Tim linked to, on his first test after running his baseline, he added a Corvette manifold and a 2nd truck muffler. That raised the HP number by 6hp at 3000 rpm. Now, I'm not saying you'd get exactly that increase on a 235 but I would think it would be somewhere in the ballpark. I'm guessing a set of Fenton headers flow about the same as the Corvette manifold did, maybe better. Oh, and IMO you don't need anything larger than 2" exhaust piping. The next test was with the addition of dual carbs. An additional 11 hp was added.

So, by bolting on carbs and dual exhaust they gained 17 hp.
You can get a Fenton or Offy manifold from Tom Langdon and the carbs that match it.

Another easy bolt-on is an HEI ignition. I like the one Tom Langdon sells. I think with those 3 "bolt-ons" you'll achieve your goal. Now, add an "848" head, and a one of Patrick's street cams later on and the ol' 235 will be puttin' a smile on your face for sure.

I have a bone stock 235 in my 55.1 1/2 ton PU.
I took it to the dyno to get a baseline (thread here) . Now I've changed to a Corvette exhaust manifold with a pair of 22" Smithy's. I'm thinking of going back to the dyno before I add the dual Carter/Webers. That way we'll have an indication of how much improvement it adds.

regards,
Leon

Wow!! Thanks waldo53.

In general I'm happy with the performance of my 235. However, I plan to pull a tear drop trailer to Yellowstone in the summer of 2011. I know that a tear drop trailer isn't very heavy but I thought a little extra power would be nice up the hills.

I have driven my truck over the pass going over Mt. Hood which is I believe a 7% grade for 5 miles. The truck pulled the hill at over 50 miles per hour in 3rd gear! This was with no load other than my wife and I. With that said, I'm not sure how it will pull with the trailer attached. I'm sure slower at least. I haven't purchased the trailer yet but I think fully loaded it won't weigh much more than perhaps 1,100 lbs. +/-

Hey Leon, let us know what the results are. This would be very interesting.

My stock '60 235 (factory specs) is 115 HP and 195 ft/lbs. torque. I cannot remember at what rpm. I have that info. somewhere...

The factory rating for my 235 in the 55.1 is 112 HP. (page 6-2 of the shop manual). I'd guess our engines are very similar. I'm expecting to see 3-4 more ft/lbs of torque at the upper RPM region (3500) due to the better exhaust.

regards,
Leon

Iron Clad-

With respect to power improvements, I highly recommend California Bill's Chevy Speed manual. It shows step by step the HP vs. RPM curves starting with a stock 216, evaluating each upgrade all the way to a drag racing setup- very cool.

http://www.amazon.com/California-Bills-Chevrolet-Buick-Manual/dp/1555611060

After reading this, going with two-single carbs is greatly preferred over one two-barrel carb, (much better volume/flow at the high end) and dual carbs with a mild cam is by far the biggest bang for the smallest buck. Dual exhaust does add some at the high end, but that's more for the cool exhaust note than for power.

Sorry- Here's a better link for the more recent edition of that book. -W

http://www.amazon.com/Chevy-GMC-Buick-Speed-Manual/dp/1931128057/ref=pd_cp_b_0