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. Increasingly stringent emissions and fuel economy standards have long remained a source of challenges for research in automobile engine technology development towards the more thermally efficient and less polluting engine. Spark ignition (SI) engines have lower part-load efficiency when compared with the diesel engines. The greatest opportunity for improving SI engine efficiency is by way of higher compression ratio, variable valve timing, low friction, reducing throttling losses, boosting, and down-sizing. Variable compression ratio (VCR) technology has long been recognized as a method for improving the fuel economy of SI engines. The concept of variable compression ratio (VCR) promises improved engine performance, efficiency, and reduced emissions.