Abstract: A method and apparatus for improving the time response of a turbo-compressor assisted internal combustion engine wherein the turbo-compressor is driven by an electric motor at a speed somewhat less than its full-load operating speed until such time as the turbo-compressor is driven at a higher speed by an exhaust gas turbine. The electric motor is provided to maintain the minimum rotational speed of the turbo-compressor when the engine load is low so that the turbo-compressor is ready for prompt response when driven by increasing exhaust gas as a result of additional load demand on the internal combustion engine.