Oil used: 30ml 80W90 GL4 / GI4 (no GK5 ! oils) I was in contact with Busch about the supercharger, but they dont give you any information (secret). Only the ammount and kind of oil for an oil change.
Its a 180ccm roots blower, up to 1,99bar pressure (theres a spring valve overpressure valve that opens at 2bar at the supercharger itself). The K15 runs with 1,7bar and the K20 with 1,95bar by the way. Same RPM as the engine itself.