Boost
Pressure above atmospheric pressure in the intake manifold. Boost is useful only when supported by airflow, fuel, ignition control and heat management.
A/R ratio
Area-to-radius ratio in a turbine or compressor housing. On turbine housings, it affects spool and flow. Smaller often responds faster; larger often supports more top-end flow.
Compressor surge
An unstable condition where the compressor cannot maintain smooth airflow at the pressure ratio being demanded. It can sound like flutter and may be harmful depending on severity.
Wastegate
A valve that bypasses exhaust around the turbine to control turbo speed and boost pressure.
Blow-off valve
A valve that releases pressure from the intake tract when the throttle closes under boost.
Intercooler
A heat exchanger that cools compressed intake air before it enters the engine.
Boost creep
Unwanted boost rise at higher RPM because the wastegate cannot bypass enough exhaust.
Heat soak
A condition where the intercooler or engine bay becomes saturated with heat and intake temperatures rise.