Most aftermarket exhausts use proper bending and pipe diameter to make power for the given application. The ones you see in the catalog follow along the lines of the oem exhaust. To me, the best way to make your exhaust flow more (other than purchasing a complete cat-back
referrably Tanabe RM) is to use a high flowing aftermarket muffler ie:Apex N-1 and have a muffler shop make custom pipes to make it exit the passenger side-less bends.