What does a test pipe do? Ive searched...

[TurboCarsOnly]

I'm just wondering what exactly does a test pipe do and what are the gains or advantages of using it in your exhaust ?

[240sxvaj]

its just a straight pipe replaceing your stock cat. and the test pipe have no comb in it

[NSRsheets]

Exactly. It's mostly used for emissions reasons. Most people make test pipes to put cats in to pass emissions and then take them out and put the straight pipe back in.