My car has longtubes and a mac shorty H with 2.5 inch diameter piping. Am I just looking for cats with 2.5 inch inlet/outlets or do they have to be specifically for teh mustang?

I see some on AM for roughly 200 bucks but I have also found a few on summitracing for like ~75 each, though those are universal.

 

Just measure a straight part of your current exhaust and find some that will fit in there say 12ibches of straight on your exhaust get 12'' race cats and weld them in any cat will work as long as its 2.5

 

I assume you don't live in CA or someplace with seriously strict emissions inspections. In most states, you can add just about any cat you want to cover the requirement. I am also assuming that you are adding cats to cover a state emissions inspection.

Personally, I would be sure to get a name brand cat because you don't want to bolt any super cheap crap in there. Good quality high flow cats flow very well.

 

Thanks guys.

We don't yet have emissions testing here but I may end up selling or trading in the car soon and I don't want to worry about "where are the cats lol" when the time comes.