An air boost system for a two-cycle engine, such as an EMD engine, which operates with a gear-driven turbo-supercharger. The turbo-supercharger is undersized for the engine, such that it is insufficient to provide air flow for a target air-fuel ratio above a pre-determined mid-load threshold. An additional turbocharger is installed in parallel with the turbo-supercharger, such that the intake manifold may receive air intake from only the turbo-supercharger or from both the turbo-supercharger and the turbocharger. In operation, the turbocharger is active only at loads above the predetermined load threshold.
John C. Hedrick; Steven G. Fritz