3" high flow cat (hollow out or let it burn up running a rich a/f) to stay somewhat legal as it could be a very expensive ticket on the street. Picked up mine new for $50 each. I prefer Borla XR-1 since they don't drone but as some board members might attest, my car is still very very very loud (318 cu in with equal length long tubes, burnt cats, and 3" all the way back with Borla XR-1 mufflers). Dump the exhaust past where you sit or you're gonna get a lot of heat and noise in the cabin.