Boost gauge

A boost gauge is a pressure gauge that indicates manifold air pressure or turbocharger or supercharger boost pressure in an internal combustion engine. They are commonly mounted on the dashboard, on the driver's side pillar, or in a radio slot.

Turbochargers and superchargers are both engine-driven air compressors (exhaust-driven or mechanically driven, respectively) and provide varying levels of boost according to engine rpm, load etc. Quite often there is a power band within a given range of available boost pressure and it is an aid to performance driving to be aware of when that power band is being approached, in the same way a driver wants to be aware of engine rpm.