If the angle at which the pipe comes from the coupler is steeper then it produces more low end. If you look at the Associated RC10GT pipe ( http://www2.towerhobbies.com/cgi-bin...?&I=LX3428&P=7
) the angle from the couple end is steeper. Now if you look at a top end powered pipe the angle from the coupler is gradual and not steep. ( http://www2.towerhobbies.com/cgi-bin...?&I=LXCKN7&P=7
). You can see the difference in the angle from those two pipes.
Im not sure but i believe that the longer the pipe is the more HP is produced and the shorter the more torque. I think this because if the pipe is shorter than there's more back pressure, which means more low end torque.