Advantages
Petrol engines have a limit on the maximum pressure during the compression stroke, after which the fuel/air mixture detonates rather than burns. To achieve higher power outputs at the same speed, more fuel must be burnt and therefore more air is needed. To achieve this, turbochargers or superchargers are used to increase the inlet pressure. This would result in detonation of the fuel/air mixture unless the compression ratio was decreased, i.e. the volume above the piston made greater. This can be done to greater or lesser extent with massive increases in power being possible. The down side of this is that under light loading, the engine can lack power and torque. The solution is to be able to vary the inlet pressure and adjust the compression ratio to suit. This gives the best of both worlds, a small efficient engine that behaves exactly like a modern family car engine but turns into a highly tuned one on demand.
Variable compression ratio is becoming increasingly desirable as oil prices increase and car buyers have an increased interest in fuel economy.
The cylinder head can be altered by using a hydraulic system which is connected to the crank shaft and responds according to the load and acceleration required..
Read more about this topic: Variable Compression Ratio
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—Ralph Waldo Emerson (1803–1882)
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—Henry David Thoreau (1817–1862)