A phenomenon that occours when a forced induction engine has more oxygen being forced into the engine than the fuel system can compensate for. This results in making the air-fuel ratio lean.

Overboost is an excellent way to absolutely destoy an engine, and it usually results from a novice engine tuner upgrading a turbocharger, supercharger, or adding a nitrous system without upgrading the fuel pump, fuel injectors, and/or carburetor.