Yes the air passes around the outter part between the rotor and housing, but is compressed as the rotors mesh together in the middle---it is a positive displacement and I don't see how they can get any more volume out of it without some fancy manipulation of rotor design to change the displaced volume in the middle without spreading the rotor centerlines and doing new end plate/housings and gears-- they also must have custom cases as the GMC cases are not 3/4 in thick--about the only thing 6:71 about this would be the mounting pattern at the manifold.