| Lowering the compression ratio allows (like Joey said) you to increase the boost. Lowering compression lowers combustion pressure, prevents pinging, detonation, knocking, etc. That is why intercoolers are used in most turbo applications to cool the air once it is compressed. By lowering the compression ratio, lowering the charge temperature, reducing the ignition advance, and using higher octane fuel, higher boost pressures can be run. Retarding the ignition and reducing the CR can also reduce power and engine efficiency/gas mileage, so there is a trade off. |