What exhaust pipe and header diameter for GMPP LS9 engine?

[dhanks]

Hi all,

Can someone help me calculate the diameter required for dual exhaust pipes and headers for a GMPP LS9?

[Schwartz Performance]

Maybe there is a mathematical equation for the perfect size, length, and backpressure for maximum horsepower, but what are you doing with the car? If the engine is stock you can use 1.875" headers, and a dual 3" exhaust. If you plan on upgrading the engine to 750+hp then 2" would probably be better.

-Dale

[1966longroof]

You can mathematically calculate the flow requirements of an exhaust system based on the total mass flow of the system (mass of the ingested air plus of the fuel), but it works out to about 2.2 cfm per engine horsepower. For a straight piece of round pipe, each square inch of cross-sectional area flows about 115cfm. So it's a matter of working forward from there. Or...... the Rule of Thumb for dual-exhaust: 2" = 289 max HP. 2 1/4" = 371 max HP. 2 1/2" = 463 max HP. 2 3/4" 566 max HP, etc.

[andrewb70]

I was reading a thread by Mark Steilow regarding his latest build. He has done a lot of engine dyno testing with Thompson automotive on his particular combo, which is a LS9 on steroids. He has a 427ci engine but uses the LS9 forced induction package. Anyway....to make a long story short, they found that the engine is not particularly responsive to the exhaust. Hence, he runs 1 7/8" shorty headers and 3" exhaust. This is on an engine that makes 700+ HP...or more...I just don't recall...safe to say more than a stock LS9...

Andrew

[alphaenvirmgt]

Dual 3" exhaust with straight thru Magnaflow mufflers. It will be loud!
Conrad