what's the size of the exhaust after the y-pipe? Also what type of muffler should I use for the single exhaust? I'm looking for more performance and I'm not really worried about noise. Thanks

 

If I not mistaken its 2.5". I have had and heard very good experiences with Magnaflow.

 

I got a magnaflow cat-back on mine. Its the single sided system made from 3" mandrel bent tubing with a 4" tip. I think it sounds great! Its not too loud, (not loud enuff for some people), and it makes a good improvement over stock. Also, it fit great and came with a lifetime warranty. I highly recommend it for its quality of parts and also value. I bought mine locally for $320 which I thought was cheap for a stainless steel system.