Im looking to have a custom 3 in downpipe made but was wondering if I should use the stock cat or get a new one? Im trying to keep the cost down and I have heard that the Audi cats are pretty free flowing, is this true? Plus I plan on having the 3 in DP go to the stock cat back. Now the stock muffler is HUGE and I want to replace it but why is it so big? Does it do something in particular that replacing with a magnaflow might mess up? Thanks.

 

u think the cats are ok but you cant beat a hp cat