i put a cherry bomb muffler on my truck and i cut the cat off and ran a 2 1/2 inch pipe from where i cut the cat off to the muffler i put the muffler on and the stock tail pipe. i think i got some power from it it has a little rumble to it not much tho i know it can breath better now.

 

I hollowed out my cat so it's still there but not restrictive anymore. Gave the exhaust a different sound. Hard to describe but sort of like a hollow echo.