i have a r33 4 door and i am using the x force system for the 2 door, but i think it is a bit short because the sound really resanates around so i did a temperary extension on the tip buy about 100mm and it made heaps of difference, the only thing is the pvc pipe didnt last to long, need a peace of 4.5 inch stainless, but all the mounts lined up perfectly from the turbo back