Edit: This is not an Audi question, just a general question. I thought you Audi guys could answer it better.
My buddy has a passat. The guy he bought it from put a custom 2.5 inch single pipe exhaust on it, and some aftermarket CAT. He just failed smog and its been determined he needs a new CAT. When we look online, we cant find a 2.5 inch CAT made for a Passat. For instance, this is the only one that pops up for his car. But it's only 2 inch pipe.
So the question is, can he use any 2.5 inch CAT? Or does it have to be for his specific vehicle? Can we grab a 2.5 made for another car if it fits?
Anyone change their exhaust from stock and had to buy a CAT not made for the vehicle? Are the aftermarkets all made the same internally, just differ in sizes externally?
Sorry for my ignorance. Neither of us have bought a CAT in ours lives.