Variable compression ratio is a technology that allows an internal combustion engine's compression ratio to be adjusted while the engine is running. This is done to improve fuel efficiency while driving at different speeds. Variable compression engines allow you to vary the volume above the piston at top dead centre. Lower ratios are required for larger loads to enhance power, while higher ratios are required for lower loads to increase efficiency, i.e. to reduce fuel consumption. This must be done while the engine is operating in response to the load and driving demands of an automobile. The maximum pressure allowed in gasoline engines during the compression stroke is limited, after which the fuel/air mixture detonates rather than burns. More fuel must be consumed to create larger power outputs at the same speed, which necessitates the use of more air.
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