It is a good idea to actually reduce the compression ratio of an engine prior to adding a blower or turbo unit, either by replacing the pistons with dished ones or by adding combustion chamber volume to the head. Also, cam timing is very critical and in this case, having a radical cam is not desirable. Therefore, if one has "hopped-up" his engine, it may be necessary to undo these things before adding boost.
The following chart shows the effect that various amounts of boost will have on the compression ratio. It is obvious that if your car is already pushing 9:1 compression, adding just 8 pounds of boost will cause some extreme effective compression ratios that will need to be addressed if the engine is to obtain any degree of reliability, not to mention the need for extreme measures to increase the fuel octane.
|Compression Ratio||2 pounds of boost||4 pounds of boost||6 pounds of boost||8 pounds of boost||10 pounds of boost||12 pounds of boost|
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