Cat Conv. Help

[emjlr3]

Alright I just got the bad news that my cat was bad yesterday. Well, ive replaced from the cat back with high flow parts so i figure I might a well get a high flow cat as well. Im pretty set on getting the carsound magnaflow cat considering that is what everyone keeps reccomending. There is only one prob...im not real sure what the in and out on it should be. Im pretty sure that my in is 3", but not sure about the out. Plus there is also different O2 sensor things or something that comes with em and im not sure to get that or not....

Ive replaced my 2k A4 cat back with american thunder but nothing else in my exhaust. So what kind should I get?

[BethAnn]

I have a catco high-flow cat, I think it's 3" for both in and out... I just had the shop put it on there with my new muffler and pipes. It was a different size than stock, but there are connectors to make it all fit. I didn't do anything different with the O2 sensors, mine are still stock and probably need to be replaced soon.

[BLLDOGG]

well, since you got the american thunder, you dont have a new s-pipe right? then its 3"in, 2.25" out