total cylinder volume at bdc divided buy total cylinder volume at tdc.

a 4.6 l engine has 35.125 ci per cylinder at bdc at a 9:1 compresion ration it has 3.9 cid at tdc.

basicaly fuel octain is teh reason you have to lower you compression ratio with a super charged engine you are putting more air in the engine causing a higher preasure at tdc and 93 octane fuel will only handle som much preasure befor it detonates.

 

Lower static compression is usually desired by those out to make a LOT of HP. Static compression limits the amount of boost a motor will take. Having lower static compression allows the motor to run very high amounts of boost. It's tough for the Honda's to run 30-40psi with 11:1 compression. I used to own an Eagle Talon and it had 7.8:1 from the factory for the first gens. The 2ng gens(95+) ran 8.5:1. My '88Conquest ran 7:1 from the factory. many pros run static compression in the area of 5:1. The reason many street cars run 8.5 or a 9:1 static compression is to make the car more responsive offboost as street cars must meet a variety of conditions. Race cars do not so they run low compression and massive boost.

 

Lower static compression is usually desired by those out to make a LOT of HP. Static compression limits the amount of boost a motor will take. Having lower static compression allows the motor to run very high amounts of boost. It's tough for the Honda's to run 30-40psi with 11:1 compression. I used to own an Eagle Talon and it had 7.8:1 from the factory for the first gens. The 2ng gens(95+) ran 8.5:1. My '88Conquest ran 7:1 from the factory. many pros run static compression in the area of 5:1. The reason many street cars run 8.5 or a 9:1 static compression is to make the car more responsive offboost as street cars must meet a variety of conditions. Race cars do not so they run low compression and massive boost.