Forced Induction Glossary
Absolute pressure: A pressure measured from absolute zero.
Absolute pressure sensor: A device for sensing pressures from absolute zero.
Air to water intercooler: A heat exchanger on a turbocharged engine that uses ambient air to cool air coming from the turbo to the intake manifold.
Atmospheric pressure: The pressure of the atmosphere at any given location. At sea level, it is 14.696 psia (101.33 kPa absolute).
Blower: A performance term for a supercharger or turbocharger.
Boost: The increase in intake-manifold pressure, produced by a turbocharger or supercharger.
Centrifugal supercharger: A mechanically driven, forced-induction system using centrifugal force to increase air pressure.
Diverter valve: A vacuum-operated valve in an air-injection system that directs air-pump output to the intake(bypass valve; BPV) or atmosphere(blow-off valve; BOV) during high-vacuum deceleration to eliminate backfiring.
Forced induction: An intake system that provides a means for the air/fuel mixture to enter the combustion chamber at greater than atmospheric pressure.
Impeller: A rotor that transmits motion such as a supercharger or turbine.
Intercooler: A radiator-like heat exchanger between the supercharger or turbocharger and the engine to cool the air/fuel mixture.
Pop-off valve: A spring-loaded pressure relief valve. See diverter valve.
Pounds per square inch (psi): An English measure for pressure or stress.
Pressure drop: The loss of pressure due to a restriction, a long line, or a small diameter line.
Pressure test: A procedure for testing the entire forced induction system for leaks.
Roots supercharger: A mechanically driven, positive-displacement blower with hourglass-shaped rotors.
Sequential (staged) turbos: Turbochargers in series, one feeding the other.
Speed ratio: A comparison of the difference in speed between two moving parts such as impeller speed and turbine speed.
Supercharger: A compressor which pumps air into the engine's induction system at a pressure much higher than atmospheric pressure.
Surge: A condition where the engine speed increases and decreases slightly with no throttle action.
Tube-and-fin intercooler: A type of heat exchanger that consists of tubes to which fins are attached to facilitate the transfer of heat from the air passing through it to the air passing over it.
Turbine: The “hot side” or exhaust side of a turbocharger.
Turbocharger: A turbine-type supercharger driven by exhaust gases.
Turbo lag: The short delay in engine response when a driver punches the throttle in a turbocharged vehicle.
Vacuum: An enclosed space from which all air has been removed, having an absolute atmospheric pressure of near zero.
Vacuum gauge: An analog or digital instrument used for measuring vacuum.
Vacuum line: A rubber-like, plastic or nylon tube used to transmit a vacuum reading from one place to another.
Wastegate: A pressure relief unit, integral to the turbine housing or mounted remotely, used to control turbine speed and therefore boost.
