Exhaust system size issues

[David H.]

Some may remember that I recently purchased a complete exhaust system from Paragon. Good price, fit pretty good, good quality.
I questioned at the time the 2" size of all the parts whereas the manifold is 2 1/2" but no one at Paragon and no one here mentioned that for my 340hp motor it might be a 2 1/2" system all the way back.
I scoured all the books and archives and found nothing to suggest that 2 1/2" for the 340hp motor would be correct.
The other night I was researching in Noland Adams book for something else and low and behold I came across one two sentence paragraph on the RPO 396 exhaust that states "While the base exhaust pipes are two inches in diameter, the 1962 RPO 583, 396 and 582 exhaust pipes measure two-and-a-half. The exhaust manifolds and exhaust crossover pipes used with these options also were enlarged".
I called Paragon today and Ken, their head of tech support, believes this statement to be incorrect. He has been restoring Corvettes for years and has never seen any of the C1 Corvettes with 2 1/2" exhaust pipes.
I would have loved to have put 2 1/2" exhaust on my brother's car if that is the way it came but everything I saw pointed to 2" being original.
Would anyone like to comment on this issue?

[William C.]

Re: Exhaust system size issues

The exhaust manifolds were 2 1/2 outlets, but the pipes then necked down to the standard 2" size pipes. On My personal '62, I had a set of 2 1/2 pipes made to the first junction, but then I used the standard system from there to the rear. I have a set of originals for a shp engine if you need a picture.

[David H.]

Re: Exhaust system size issues

But is the Adams book correct or is it incorrect? is my question.

[Richard T.]

Re: Exhaust system size issues

The book is correct but what he doesn't say is that the high performance exhaust pipes used the standard 2" pipe with a 2 1/2" flange welded on. The rest of the system is 2". This is how it was done by GM. Rich

[Anthony P.]

Re: Exhaust system size issues

William,

Would you please post that picture of the originals, including showing the flange reduction?

My 2nd question. You mentioned that you had a set of 2.5" pipes made to the first junction. Why did you do that, since there is still the restriction of the mufflers and smaller tail pipes? (Was it to somehow improve the front cross over function)

Thanks again,
Tony

The exhaust manifolds were 2 1/2 outlets, but the pipes then necked down to the standard 2" size pipes. On My personal '62, I had a set of 2 1/2 pipes made to the first junction, but then I used the standard system from there to the rear. I have a set of originals for a shp engine if you need a picture.

[Jerry W.]

Re: Exhaust system size issues

Ignore the "cherry bomb" mufflers in this pic but you can see typical "neck down" from 2-1/2 to 2 inch pipe just below the manifold flange

[William C.]

Re: Exhaust system size issues

As the exhaust travels along the pipe, the volume decreases as the gas cools. By just doing the front pipe, which I needed anyway as I was going from headers, I thought is was a decent "half a loaf" compromise. Have no real performance data either way, and wasn't doing a restoration, just eliminating the headers, but I thought it was a logical compromise from where I started (Headers)

[David H.]

Re: Exhaust system size issues

Not to kick a dead horse here, but why would GM do this?
If you have a 2 1/2" manifold, and a 2 1/2" flange, by necking it down to 2" doesnt that create back pressure in the manifold?
Was it just because the 2 1/2" pipe wouldn't fit without hitting somewhere?
Doesn't make a lot of sense to me. 2 1/2" pipes would sound better too!

[John H.]

Re: Exhaust system size issues

Not to kick a dead horse here, but why would GM do this?
If you have a 2 1/2" manifold, and a 2 1/2" flange, by necking it down to 2" doesnt that create back pressure in the manifold?
Was it just because the 2 1/2" pipe wouldn't fit without hitting somewhere?
Doesn't make a lot of sense to me. 2 1/2" pipes would sound better too!

David -

Most likely because the clearances between the O.D. of the pipes and the two holes in each side of the frame "X"-member and the rear springs were marginal to begin with at 2"; would have been very difficult to install them without rattles with 2-1/2" O.D. pipes.

[William C.]

Re: Exhaust system size issues

If you do a search in the archives, Duke did a very good analysis of the temperature-volume relationship of exhaust gasses and the relation to performance. The essence of it was the the effect of exhaust pipe diameter matters less the farther away from the exhaust manifold due to the cooling of the exhaust in the pipes reducing the volume. Remember you are talking about 1962 here, and yes, the farther back you go the more issues you have in the holes in the frame and body.

[David H.]

Re: Exhaust system size issues

Jerry, that is exactly what came off my brother's car. Cherry bombs and welded together. Had to cut it off with a saws all.
OK, so 2" pipes are correct and will pass judging?
Good, I was not looking forward to removing and returning and ordering an new system.
I just got my dashboard box built and hooked everything up. Built a new gas line from the pump to the carb today. May actually be able to start it soon.
Thanks for all the input on this one guys. I really appreciate the discussions.