Another way to improve the Exhaust note is by installing an X-pipe, altough the traditional design has a great sound and great overall performance the X-Pipe is for those of you looking for a deeper exhaust note, due the the extremely well balanced exhaust flow this design will give you a better sounding exhaust vs the traditional design, since the balancing of bank 1 and bank 2 is better with the X-Pipe the results will be better sound, the traditional 200 cell cat-pipes retain the OEM design and hp gains are distributed more evenly, with the X-Pipe the power will mostly be on the higher RPM range. Check out the newly designed 997 NHP X-Pipe here http://www,maxspeed-motorsports.com/997catpipesx.html