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The Atkinson cycle uses additional linkage between connecting rod and crankshaft to achieve the higher expansion ratio. Miller cycle is done by altering the intake closing event. The best way is a custom ground cam but you can just retard the stock cam to achieve almost as good results. 5-10 deg. should allow for a 2 point jump in compression ratio. I run 10deg. retarded in my own engine 12:1 cr on 87octane fuel. In the warmer its a little bit to much (ambient temperature over 70 deg) I just blend in about 50% 93 octane to keep it out of detonation. A dedicated water/methanol system will get the job done also. Low end torque is down at speeds below 2,000 rpm but over that it makes more power then running it straight up.
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