Originally Posted by MADDOG
totally agree with that statement.
With the stock muffler any gains you'd get by going to a high flow cat (not really needed unless you plan on camming the engine and opening up the heads a bit) or a better Y-pipe will be negligible and defeat the purpose of installing those parts.
The aftermarket mufflers will improve flow and the longer they are, the quieter they tend to be if you are worried about noise.
Good to know. Since the general census is not to expect and performance or mileage gains with a high flow muffler, I was curious if changing cats and the y pipe only could produce any gains and could cost about the same money.