I dont think you can do it with the SCT....

 

So let me get this straight, i'm running stock exhaust except for the pypes axlebacks on my '05 GT and if I get the pypes h- pipe and keep my stock cats it will be louder? Also should I get the h pipe or the x pipe?

 

pypes h-pipe deletes the cats. ....its a straight pipe.

 

So can I keep my cats and make it louder or does someone make an h pipe with hi flow cats?

 

its tough because the removal of the cats is why they are so much louder. Get new headers could make it louder also.