Have an 02 TA a4 with a full catback exhaust y pipe and shorty headers which I don't think do too much. I was wondering if hollowing out a set of cats and replacing the ones in right now will make a difference or not? Or should I just buy some LTs and swap before cali smog lol

 

Get LTs and a Y pipe. Shortys are just for sound, and in my opinion don't sound that good. There are fake Cats that actually have a pipe that goes through it and is not just a huge expansion chamber like a hollowed out cat. I have a pair but I will be using them. Got them off of here so I don't know where to buy them. Just search around for them.

 

get some LTs and enjoy having more power.

 

Hollowed cats will be "boomy" and not that great at higher
flows, they will create some turbulence. If you want to
lose the restriction, get some Mufflex tubes.