A turbocharger system for an air-throttled engine includes a variable flow expander (VFE) in the intake air conduit system that supplies intake air to the engine. At part-load operation, the VFE expands the air by an amount that is controllable, and thus regulates the air flow as needed by the engine. The power extracted by the VFE from the intake air flow is fed to the turbocharger, which helps to achieve quicker turbocharger response and improve scavenging of exhaust gases from the engine. The VFE can be a variable expansion ratio turbine.