Headers or Test pipes or both with stock exhaust?

Originally Posted by Megan370z

Your statement is wrong.

the same exhaust heat is being thrown down the exhaust. it does not matter cats or not ... I shouldn't have added in my statement about heat because its wrong... because you cannot produce more heat after the combustion is done .... that 600F+ you are talking about is just at that location the heat will generally be (as per what you are saying) at 600F in the cats .. if you have a cats at the Y-pipe (xyz y-pipe) the heat will be less.. because its farther down the stream ....