if you piss off a highway patrolman and he starts picking around your rig and finds no cat....the exhaust shop I go to told me it is a fine of over 10,000$ if convicted!! I don't know if they are BS'ing me or not but I know if it came with a cat and it rolls on pavement, you need to retain it. Hollow it out if you want a more free flowing device, personally I hate zuk drivetrain on the highway because any little restriction makes it a complete piece of crap!! I am sick of mine!!