I got this graph from Corky Bell's book "Supercharged!" (http://www.amazon.com/Supercharged-T...e=UTF8&s=books) that is about supercharging engines. Corky Bell is a Mechanical Engineer that used to work on aviation motors, but has changed over to automotive and now runs his own performance business. Here is his recommendation on exhaust sizing for supercharged motors. I modified it by adding the lines to show what each size was capable of. These numbers are at the crank of course.

 

That seems a little small, but going by it the GMPP exhaust would make a lot of sense!!

 

I thought the same thing, but he is a well known tuner and aftermarket builder so who am I to argue.

 

Corky is the **** but thats messed. If you making 300hp on ur SS and have stock exhaust and swap out for either 2.5 or 3.0 there will be a difference.

 

The stock exhaust on a SS is 2.5" it's just the muffler that is the restriction.

 

no it necks down in a number of locations

and yes this seems a little small to me as well

 

Man, did I ever go over kill then.....

 

I think the problem with the stock exhaust is that it jumps around in size making it more difficult to flow smoothly.

This would explain how Jonel still got 12whp/10wtq out of a GMPP catback which is 2.25" all the way through.

This is crank rated, so 300hp with a 12%-15% drivetrain loss would be 255-264 at the wheels. That seems to make sense too me. That is about GM Stage 2.

 

Overkill FTW.

 

could be because of the variations in size, but some motors actually benefit from it becaue of the flow patterns created. NHRA pro stock cars have varying exhaust diameters throughout their exhaust system, some of the piping even necks down to 2.25 in some places

 

Yeah, step headers use the idea of expanding gas and change tubing size, but with gains all the way across the rpm range on Jonel's dyno prove that the full 2.25" GMPP Performance exhaust is better than the stepped Stock exhaust.

 

agreed!

 

o ya, at the O2 bung its 2"

ok thats better