Abstract: An internal combustion engine including a turbocharger and a controller for the turbocharger. The engine has an air intake to receive a charge of compressed air while the turbocharger includes a compressor connected to the air intake. The turbine is connected to and driven by exhaust gases of the engine and drives the compressor. The controller limits the pressure of the compressed air charge to below a predetermined pressure at high engine speed. The engine further includes a positive displacement compressor connected to the inlet of the turbocharger compressor to supply compressed air at low engine speeds, and a direct drive for the positive displacement compressor. The drive is selectively operable and able to be selectively disabled.