[comptiger5000]

I agree that newer OEM cats are much better flowing than they used to be. Also, BGD is right about the header thing. If you're going to put in a high flow cat, it's a good time to re-do the exhaust. If you can get long enough headers that aren't too huge, they won't hurt your low end torque. Plus, then you can wrap them, and maybe even the Y pipe, so the cat gets hot faster, and absorbs more heat, allowing a larger, higher flowing cat to work effectively.