Ok been hearing that 3 inch will kill me or at least untill I get the supercharger that G.M.
is gonna sell whenever. Thing is I don't want to do an exhaust system twice, and being new to the whole 4 cyl engine thing I also don't want to f--k it up. So I'm turning to you guys for your help, I know with a blower 3 inch is great but why do I keep hearing if I run it in an n/a application it will kill me? I mean don't these things run better with less backpresure, or even open header, so why is 3 inch gonna hurt the performance? It just doesn't make any sence to me. I had dual 3 inch with an "X" pipe on my old firebird and it was awesome waaay beter then the 2 1/2 that I took off and this was before I did
all the work to the engine. I'm confused shouldn't the fact that the cat will be directly
behind the header won't this provide some back presure?

Any help would be great appreasheated ( spelling )




Semper Fi SAINT. May you rest in peace.

From what I've experienced and been able to tell, from the cat-back really doesn't make a big difference, I may be completely wrong here, but say you were to simply put a turndown after the cat, it doesn't matter what the piping size is because the exhaust is out of the system.

What matters most if you're n/a or s/c is the collector size at the header, once the exhaust flow has already been slowed down, you can't speed it back up. So with that being said, as long as the piping behind the cat is the same size or larger than the piping from the collector to the cat, than you're fine.

Seeing how you're going to be going with the s/c, the header you get you'll want to make sure it has the largest collector size possible, 2.5" is the largest i've seen, but you might be able to find 3" somewhere. And then make your cat-back the same sized piping.

This is just my logic as I have never really studied auto performance anywhere. When I had my super-charged four banger that's what everyone told me. Good luck!

The thing for our cars to make the most power is to have MAXIMUM EXHAUST VELOCITY. as it turns out, for a n/a car 2.25" is the best becuase it will produce the best exhaust velocity. this is another reason to keep a cat on a n/a j-body, it keeps the exhaust gasses hot longer, therefore creating more velocity. Now for a a boosted car, 2.5" or 3" is best. i would say get the 2.5" and just deal with the slight low end power loss till u get the charger.


this is my sig

Forgot to mention the header I have is a pacesetter and the collector is 3 inch. That why I was figureing on just keeping the system 3 inch all the way till it hits the "Y" pipe that leads to my 2 mufflers. Don't our cars do good with an open header? If so wouldn't the 3 inch do almost the same thing? I'm not trying to sound like a smart ass I'm just trying to figure out which is the best way to run. Thanks again guys




Semper Fi SAINT. May you rest in peace.

On a N/A cars the exhaust velocity is extreamly important. That velocity still crates a scavaging effect for the next exhaust pulse, pulling it along, instead of the engine "pushing" it out. This scavaging effect is what helps pull the next A/F charge into the cylinder, which creates the increase in torque.
With boosted applications, the exhaust pulse has a much greater volume, which just need to be moved out of the way and it can be "pushed out" without any detrimental effects on the torque out put of the motor. This is because the next A/F chage is being pushed into the combustion chamber, insead of being drawn into the chamber.

im running a full 2 1/4" exhaust , and dont plan to use anything larger


atleast untill im running a constant 10psi or higher then ill move to 2 1/2"

/\ /\ /\ That small and your boosted? Does it run ok? i believe the G.M. blower is rated to around 10psi but since this is oly the reviews I've read from the SEMA shows I don't realy know.






Semper Fi SAINT. May you rest in peace.