I just bought a 2008 g37 6 speed and it came with megan racing test pipes, and a hks muffler (but not the full catback just the muffler part welded on), and it has a resonator. Is this setup good? if not any opinions too what i should change.

 

Well you are the one with the setup so tell us is it any good? In terms of performance you already have the cats and stock muffler removed which are the biggest restrictions so you would only really see more gains by going with some larger piping or something like a true dual system. Anything else would be purely for sound/looks.