dunno, K&N have been around longer and the air feed pipe I have on mine (dunno if standard) is a healthy size. Basically is makes a hell of a noise and when you open it up the engine develops this bassy scream (which is ace, but the neighbours complain
). Ill get a wav up later if i can, it certainly roars and rattles throughout the rev range.
all in all im led to believe that the K&N is the ONE for sound, but personally Ive not heard a PiperX before.
the closed carbon ones are for performance more than sound, again, not heard one but general consensus is that they dont really make a great deal of noise. ideally someone thats had both needs to show up... (anyone...)
BTTT