But how? How does an increased compression ratio translate into more power? Efficiency. Efficiency is defined as the ratio of fuel input to the power output. Since all internal combustion engines work by extracting energy derived from an expanding heated medium in a confined space, it follows that the largest difference between the volume of the unexpanded cold charge and the fully expanded hot charge needs to be as large as possible. Increasing the compression ratio is a way to maximize this.
The balance of boost versus compression ratio have been a tuner’s challenge for years. Today, the average high-performance street or strip turbocharged four-cylinder race engine typically has a compression ratio of 9.5:1, with some even running compression ratios as high as 11.5:1 or more on alcohol or E85. Years ago this sort of combination was not possible, typically the higher the boost pressure, the lower the compression ratio of the engine had to be. Modern technology allows our generation to experience the best of both worlds, high boost pressures with high compression ratios.