The only modification required that the shop would do is to extend the tip a little bit so it fits just right (since you have a sedan, and the MS3 CBE fits a hatch). Just a little welding work, nothing big. If you delete the 2nd cat and have them fab up a straight pipe for you, you can look to gain up to 9 hp! If you keep the 2nd cat, I think you'll see gains of just 3-4 hp (somewhere around there, I'm not too sure on the numbers).