An assembly for controlling air flow to an engine includes a first supercharger(20) and a second supercharger (22). The superchargers are arranged in parallel with one another and in series with the throttle (70) in the air flow to the engine cylinders, and are configured to be operatively connectable with the engine upstream in the air flow to the cylinders. The assembly includes a load device (38) selectively connectable to the first supercharger (20) and selectively alternately operable to provide energy to or receive energy from the first supercharger. The superchargers are configured to be separately selectively operatively connectable with the throttle and the crankshaft to enable different modes of operation.