When I got my headers the shop put an off road pipe in. I loved the sound. Really throaty for a GM. Got comments for GT drivers. I was told I needed more backpressure so put on a high flow cat. Car runs the same to me. No noticable difference, but really quiet and weak sounding now. Does the cat make much difference in performance.

More backpressure? That must be why cars with headers open are slower.

was it the guys that you were beating in all the races t hat told you that you needed more backpressure? hell, from what i understand about the way exhaust gases flow, ANY backpressure is bad. but, then again, you also don't want too much scavengiing, either, as the air/fuel mix will get sucked right thru the combustion chamber druing overlap- which makes it all just wasted gas.