Ok i know a y-pipe is a pre-cat. but all that means to me is that it only helps when the engine is cold. Now do all stock cars including maximas come w/ y-pipes or is it just considered a stock exhaust*

 

they have a stock ypipe(that has a precat) thats restrictive as hell. aftermarket is all free flow

 

the stock ypipe connects the two exhaust manifolds together. they have a precat at each exhaust manifold. an aftermarket ypipe removes the two precats and smoothes out the piping. the gains are almost ALL from removing the precats.