My friend punched out his cats on his 5.3 truck it sounds great and loud
How much if any hp did he gain?
Has anyone done this

 

One of the guys over on the truck site did this and dyno'd his truck right after. He gained 7rwhp and 8rwtq in the upper RPM's. His truck wasn't stock though, he had a cam, tune, cai.

 

I find a better result if you just delete the cats all together. When you "gut" a converter it is a big open dead zone for exhaust pulse and pressure and it causes turbulance. Just order you an offroad Y-Pipe from pacesetter or have you one made by and exhaust shop. It don't take no time to set up a jig and weld up your own custom Y.