i wanted to know the opinion of other 350z owners on what is the best exhaust, intake, headers, y-pipes, or either race pipes or cats

 

what you want to know is subjective..
My opinon is that the best stuff is :
Exaust - Nismo
Intake - Stock w/ K&N or nismo drop in, get a spacer (AAM ) or new plenum (crawford) instead...
Headers - Strup
Y-pipe - Nismo
Cats - Helix High Flow

 

every bodies gonna be different but.....
exhaut: nismo
intake: new injen cai w/ crawford plenum
headers: crawford
y-pipe: jic
test pipes: xerd(best bang for buck $89 and no CEL Light!)