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Actuator
The pressurised (or could be electrical) canister which provides movement for wastegate valves or variable geometry systems.

Bearing Housing
Centre housing which carries the turbo’s bearings and seals.

Boost
Pressurised air from the compressor.

Compressor Housing
Casting with volute shape, collecting the air and converting the velocity into pressure.

Impeller (or Compressor Wheel)
Radial wheel to suck in the air and accelerate it into the volute of the housing.

Pressure Ratio
The compressor boost pressure divided by the compressor inlet pressure to give a ratio.

Sequential Turbocharging
Two, dissimilar sized turbos, working in series, but not together. Use of a small turbo at low engine speeds, and then switching to a larger turbo for higher speeds.

Turbine Housing
Casting, with scroll shape, to collect and accelerate the exhaust gas into the turbine wheel.

Turbine Wheel
A Nickel alloy radial flow wheel, converting the exhaust gas energy into rotational speed, in order to drive the compressor, to which it is mechanically connected via a shaft.

Turbo Lag
Slight delay in engine response, from pressing the accelerator pedal, to when the turbo boost increases and the vehicle speeds up. Most noticed at low engine speeds.

Two–Stage Turbocharging
Two, dissimilar sized turbos working permanently in series, to achieve higher pressure ratios and power from a small engine size.

Twin Turbos
Two, same-size turbos working in parallel on usually 6, 8 or 12 cylinder engines; each turbo working on half the no of cylinders, to avoid fitting a too large turbo.

Variable Geometry
Turbine A device, ( generally with moving vanes ) to allow higher velocity of the exhaust gas into the turbine wheel at low speeds for better engine performance and response at these lower speeds.

Wastegate
A by-pass valve around the turbine wheel, to allow use of a small turbine housing size for better engine performance at low speeds.