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Had a chance to pick up a split exhaust manifold for my 235". If I do nothing else to the engine, will I notice a bit better performance with dual exhaust? Logic says yes, but technically?

I can't lay my hands on dyno results for a 235, but in the May 1955 HRM article about Frank McGurk's dyno test on a 261 , he measured about a 5% improvement in peak torque and horsepower by installing a Corvette six exhaust manifold on an otherwise stock 261. The improvement on a 235 might be slightly less. As I recall, another HRM article in 1953 reported about a 3% improvement in peak HP by installing a split manifold on a 216 with dual carbs and some other mods.

Hoyt

I put my 235 build through the DeskTop Dyno computer program and it came back as 170 HP. I don't really believe that but some of my more knowledgeable Inliner friends say it isn't far off. Well whatever. I just know that time spent on the heads milling and porting is time well spent. Then do the intake and exhaust bit along with a little better cam and carbs and there you are. Don't forget the ignition, it is a big improvement.

I have seen 302' Jimmy's put out about 700hp naturally aspirated. Probably worked out to about $1000 per hp, HA. But darn that thing would go.

HP gain from 'split' stock manifold would be minimal when compared to custom headers or Fentons. You may want to check with Patrick's in AZ for more info.
www.patricksantiquecars.com

I'll have an opinion tomorrow.
I have a dyno appointment for 10:00 Saturday morning.
I've added a Corvette exhaust manifold and a pair of 22" Smithy's to my otherwise stock 55 235. I got 81 HP in stock trim.

regards,
Leon

It will sound cool! Duals and cherry bombs sound nice.

302' Jimmy's put out about 700hp naturally aspirated

I assume that's with 400 hp nitrous?

I got my Dyno results.
The 235 with the Corvette manifold made a max of 87 HP and 176 ft-lbs of torque.
That's a gain of 6 HP or about 7% over the stock configuration. Pretty close to the McGurk report.
Here's a chart.

YMMV.

regards,
Leon

No Panic it's actually a very custom built race engine including an aluminum 12 port head and more goodies thanI can list. It also is the world record holder for the 1/4 mile in dragster form. Belongs to a friend of mine and it doesn't have nitrous but it does use nitro fuel. Hard to belive I know. But is also has been bored to 320 cubes so that helps a little I suppose.

Leon,

Good work and good results. Thanks for running the tests and sharing the results. Does anyone have similar results on a split manifold and Fenton headers? The conventional wisdom is that the Corvette six manifold is better than a split, but that the Fentons are better than the Corvette.

Hoyt

it doesn't have nitrous but it does use nitro fuel

As I said...

Not the same thing. Anyway if you choose not to believe it that is fine by me. As I said, I understand its difficult to accept.

It's not "difficult to accept".
Nitrous oxide and nitro-methane are not the same substance, but for racing purposes nitro is an even stronger power adder (see Pro Mod rules).
My point is that you accidentally forgot to mention that tiny little detail (gasoline is not the fuel), as if it were of no consequence. My objection is that the conclusion you permitted to be drawn from your remark is (since all prior remarks dealt with pump gas) that a N/A GMC engine produced 700 hp on gas.
Anything over 350 would be quite remarkable.