ok so i have a catback exhuast with a flowmaster 40 series. i am getting ready to go have a "test pipe" made to bolt in where the cat. does so i can bolt the cat. back in when it comes time for smog. but i was reading about gutting the manifold and im thinking about doing that as well. if i do this and run eliminate the cat. and just have it running through the muffler and out the side with it have any problems with back pressure or anything like that?? also what about performance gains??