im not very familiar with exhaust, but what is the difference between a catless downpipe, and a stock catted downpipe that had the material cleared out of it?

 

I think you ara talking about testpipe (your cats). downpipw is just a pipe between the cats and the exhuast. I never heard it has anything inside

 

i have the 3.0... the downpipes what connect to your headers right? and go the rest of the exhaust, and the cats are in there, but with the catless downpipe obviously theres no cat. just a straight pipe to the rest of the exhaust

 

my bad... yeah

 

You would get a little more HP out of the Test Pipe (TP) than hallowing out your cat. However, unless you get a non-fowler adapter for the O2 sensor you will throw a code on the (TP). With a TP you will not pass emissions tests.

 

The catless flows a lot faster since its a straight shot. The cat has a larger diameter pipe in the middle which slows down the velocity in which it exits. It also deafens the exhaust note.