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Better to have very high cpmpression ratio with reductions made by valve timing and or lift-overlap. I think that is what Mazda is doing with the skyactiv engines. 14 to 1 on pump gas. Probably only 14 to 1 rarely, but 7 to 1 at MAPs of 50% of atmospheric pressure. Add a turbo to that compression ratio! One of the keys to their design is the 5 separate injection pulses in every combustion stroke, occuring after TDC with no posssibility of pre-ignition since the fuel is not there to ignite prematurely.
regards
Mech
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