The cheapest way I found to add a little sound and maybe a few HP is the Fabspeed cat bypass pipes. But I am loving the sound and performance that I get with TTP headers and high-flow cats going into a stock muffler. I tried aftermarket mufflers, like the Gemballa, with the header/cat rig but it was too loud for my tastes. The problem with the TTP rig is a big one and it is $$$,
Ed
