hi tom, just make sure u fit your open pod filter at a nice spot with heat shield, it is really helps a lot, mine is without heat shield cos i place it at a funny place : ) so under hot weather really feel underpower, only works well at nite time...
some said 4-2-1 is meant for torque, and 4-1 is meant for hp, but now there is many design, the length of the four pipe from engine till the first combined area is the only way to define it is torque type or hp type, shorter for torque and longer for hp ( i think so, dun scold me if i m wrong : ) )