It's oval pipe and doesn't effect the flow. Check my gallery for the dual exhaust pics. Two mufflers would be put where the original single muffler went or you can do what I did and get a dual in dual out that acts as two mufflers welded together (separate chambers on the inside). The two mufflers next to each other looked two ricey for me. And to answer what it does for the car, well let's just say that redline comes way too early. The car feels like it can pull for at least 500 - 1,000 more rpm. Time to get that computer tune.