Well I got the car completely sorted and I now need a cat so I can smog my car. I have a S4 N/A with a Racing Beat down pipe, and a Apex N1 cat back. I have a Pre-silencer on right now, but I am going to need a cat, and was wondering what cats would bolt in. I don't want a "high flow" cat, just one that works really well(I won't be using it when I am done smogging the car).

 

Would the S4 Main cats that Mazdatrix sell work? Could Is there any other ones that would work?

 

You can try the high-flow version made by Bonez. I have heard that they work about as well as a stock one where emissions are concerned.