im thinking about buying ap's 13.1" brake upgrade kit is it compatible with stock rim clearance or do i to upgrade my rims as well? any other advice??

 

AP is a very respectable brand, and it should clear inside all OEM wheels, only thing that would make me think twice would be 2003 17" wheels due to the diameter required to clear 13s, but even then it'll probably fit

 

it clears all factory 350Z wheels, 17's included

 

Welcome. Brake vendors provide templates for their brakes. You put the template on a piece of cardboard, cut it out, and put it inside the wheel to check clearance.