i gotta high flow cat along with headers. 2.5 cat back, cold air intake, on my D16Y7 does great for what it is. i've heard like there saying though that it does do wonders with a test pipe..but o well. new exhaust will have to be made when i swap...as far as emmisions go, i don't have to worry about them, lol ..when you look at my highflow cat, there's nothing on the inseide btw...