Abstract: A rotor-shaft subassembly (33) is disclosed of the type for use in a Roots blower supercharger. The subassembly includes a rotor (39) mounted for rotation on a driveshaft (41) at forward (49,53) and rearward (57,51) axially spaced-apart locations. The rotor (39) is a cast member with each lobe thereof (61,63,65) defining a hollow chamber (71,73,75). The rotor includes a cylindrical web portion (67) disposed axially between the forward and rearward locations. Each lobe cooperates with the web portion to define a core opening (81,83,85) adapted to facilitate removal of a core from the hollow chamber after completion of the casting process. Each core opening provides open communication between its respective hollow chamber and the shaft bore, and each is disposed axially between the forward and rearward locations, so that after the rotor is press-fit on the shaft, there is no leak path of pressurized air into the hollow chambers.

Abstract: A rotary positive displacement blower (10) of the Roots-type having inlet and outlet vents recess (60,62) for reducing fluid pressure build up in spaces between meshing, helical lobes (34a, 36a) on rotating rotors of the blower.