The Califonia trucks had more emission stuff than 48-state trucks. Depends on where you reside as to whether you can monkey with the cat and get away with it. I prefer to operate under the "Don't ask - Don't tell" scenario of emissions compliance - or, as somebody else on this board pointed out, just play dumb - "I bought this truck used with this exhaust system already on it. Yeah, I think it is a bit loud, too. What do you mean it doesn't have a catalytic converter? Are you sure?"