The purpose of a blowoff valve is to relieve the pressure on the blower impeller in a centrifigal style blower. When the throttle closes that air has to have somewhere to go or it would be trapped between the impeller and Throttle blade, so the blowoff valve lets the air escape and relieves the pressure off the blower impeller. With that said, the path from the intake to throttle blade has no significance in a roots style blower since the blower is after the throttle blade it would have to be inside. Does that make sense to ya?