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Message: <blockquote data-quote="ALBundy" data-source="post: 396921" data-attributes="member: 15">Glock, There are two types of compression ratio, first is the static compression which is your engine's compression ratio, for most BMWs it is 10.5 to 1 (325s) 10.2 to 1 (328s)  and etc.  The Japs like to lower the compression and have high turbo boost, to increase the effective compression (there are plenty of sites where you can calculate your effective boost), ie; key in your static compression and boost level and it will give you the effective compression. The Europeans, usually go the different route, high compression engines 10.5 to 1, with lower boost. The Golf GTi, BMW's 335i all have high compression engines with a boost from 0.8 to 1 bar. This is more fuel efficient as the high compression engines inherently produces more torque and hp.  I have seen many folks lower their compression in order to increase the boost level, but its a double edged sword as the higher boost level will need to overcome the lower static compression, let alone the lose of low end torque before the turbine kicks in.  Cheers</blockquote>