So I am wondering, what is better performance wise, Open headers or a fullMac 2.5" exhaust system or something equivalent. I also would like to know if anyone knows the differance in power between catted and non catted H pipes. This is ofcourse assuming your car is tuner for whatever set up it has.

 

Assuming you tuned specifically for it, open headers would yield the greatest power. Of course a tune made to optimize on open headers would suck when you reinsatlled the rest of the cat back system.

Generally moving a good set of cats on a V8 application is worth about 10 RHWP. Many high flow cats on the market can loose far less than that.