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Message: <blockquote data-quote="ALBundy" data-source="post: 488583" data-attributes="member: 15">Actually there is more to it. What you have just describe is the static compression ratio. However in an operating engine, static compression is no longer the measuring yardstick. For normally aspirated engines, it's the dynamic compression ratio. Dynamic compression ratio differs from the static compression ratio due to the lift and duration of the camshafts.As for forced induction engines, the measuring yardstick is effective compression ratio. This is due to the additional boost pressure from the turbine. The philosophy of the European manufacturers differ from the Jap where European forced induction engines have a relatively higher static compression but lower boost. This help to improve torque at the lower rpm  range and more fuel efficient where as the japs have lower static compression but higher boost. There are various sites that can calculate the effective compression if you decide to change your pistons and turbine. So in a nutshell, turbo cars are running higher effective compression than the dynamic compression of the NA engines. As for 10.2:1 static compression ratio, as of today's standard it is no longer considered high as plenty of normally jap engines are running 10.0:1 and some even higher.</blockquote>