Not too long ago me and friend took the main cat off and hollowed it out to make a better flow and sound. It does sound better, not sure if there is any horsepower increase but now when i am going and rev it out to about 7500 RPMs it back fires alittle, is that hurting anything? Does hollowing out the cat give me any more horses?

It might, but actually taking off ur carts will especially on a turbo, it will backfire like crazy that way, shootin mad flames yo.