2" vs 2 1/2" exhaust

[Ryan Clark]

I have a question concerning HP for a 327/300 '65 with different exhuast configuration. I know there has been recent discussion concerning side pipes and the chambered under car exhaust resulting in a HP loss as opposed to the original 2 1/2" under car exhaust.

Now, does the 2" under car exhaust restrict flow and result in a measurable loss in HP versus the 2 1/2" exhaust?

Curious,
Ryan #35188

[Robert C.]

Re: 2" vs 2 1/2" exhaust

I would say "yes" as the high HP optioned cars have the 21/2" vs the 2' for base cars.

[Bill Clupper]

Re: 2" vs 2 1/2" exhaust

Indeed, the ONLY difference between the 250 and 300hp engines in '65 was the intake and carb move from WCFB to AFB, and the exhaust upgrade.

[Joe L.]

Re: 2" vs 2 1/2" exhaust

Ryan------

I also think that there is some power to be gained from the 2-1/2" exhaust system, particularly on pre-1966 small blocks which use the 2-1/2" outlet manifolds to go along with the 2-1/2" exhaust pipes. Post-65, ALL small blocks used 2" outlet exhaust manifolds whether they otherwise used 2" or 2-1/2" exhaust. I think that any real benefits of the 2-1/2" exhaust likely occur at the higher RPM range.

One other thought to keep in mind here, though, is this: for 1969, the most powerful engines ever used in Corvettes, the L-88 and ZL-1, were equipped with 2" exhaust as were all other 1969 Corvettes.

[Walt McGaw]

Re: 2" vs 2 1/2" exhaust

Ryan,

I was told that on a 2" exhaust, you could overcome most of the difference in performance decrase from the 2.5" by installing a crossover pipe. I had that done on my car when the exhaust was replaced because the shop didn't want to do a 2.5" because of clearance. They said the crossover on the 2" exhaust would make it *almost* as good.

I don't have anything to compare it to prior to having the work done, but I am happy with the crossover for the most part.

Walt

[John C.]

Re: 2" vs 2 1/2" exhaust

Just a clarification of which I'm sure everyone is aware but no one mentioned, the 300 HP only got the 2.5" manifolds if it was equipped with a manual trans.