A supercharger (12) with two separate sets of rotors (22, 24) arranged in parallel with one another is provided in an engine assembly. Both sets of rotors are used to boost air flow during high engine air flow conditions, and only one of the sets of rotors is operable to transfer torque generated by the throttling loss pressure drop as stored energy in a load device during low air flow conditions. The captured throttling losses may be electrical energy stored in a battery via a motor/generator such as during vehicle cruising.