page_title: Turbocharger
section_title: Variable-geometry
hierarchical_section_title: Turbocharger / Key components / Turbine / Variable-geometry
caption_attribution_description: Mondial de l'automobile, Paris 2006
context_page_description: A turbocharger, colloquially known as a turbo, is a turbine-driven, forced induction device that increases an internal combustion engine's efficiency and power output by forcing extra compressed air into the combustion chamber.
  This improvement over a naturally aspirated engine's power output is due to the fact that the compressor can force more air—and proportionately more fuel—into the combustion chamber than atmospheric pressure alone.
  Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Today, the term "supercharger" is typically applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared with a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive. Twincharger refers to an engine with both a supercharger and a turbocharger.
context_section_description: Variable-geometry or variable-nozzle turbochargers use moveable vanes to adjust the air-flow to the turbine, imitating a turbocharger of the optimal size throughout the power curve. The vanes are placed just in front of the turbine like a set of slightly overlapping walls. Their angle is adjusted by an actuator to block or increase air flow to the turbine. This variability maintains a comparable exhaust velocity and back pressure throughout the engine's rev range. The result is that the turbocharger improves fuel efficiency without a noticeable level of turbocharger lag.
caption: Garrett variable-geometry turbocharger on DV6TED4 engine
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