Silly question about catalytic converters

[Westylifestyle]

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.

http://www.summitracing.com/search/Y...e/?Ns=Rank|Asc

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.

Thanks gents!

[4AudiQ]

Here is the CAT I used on my 1995 Audi Sport 90 Quattro.
Summit Racing (CTO-6806)
It does not have to be car specific, if you are just replacing the CAT.

[aTOMic]

If the car's in Cali, there is some extra reg he'll need to meet as well IIRC. Mo' money of course.

You'd have better luck posting with the actual question in the title, in a forum for that model (B5) I think.

HTH (a little)
-Tom