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which is more important - dyno time with a lower CR motor to get an optimized timing curve or to increase the CR to gain more power but having less ideal timing?
i realize that increasing CR and adding twin plug so the timing can be set for greatest power/torque is ideal but how much is the increased CR adding vs the better timing?
The correct answer to your question is "it depends". There are so many variables, temperature, octane, mixture, piston shape, bore size, etc for an absolute answer. If by "more important" you mean higher output, output increases around 4 to 5% with each point of compression (within a range, and up to around 14:1). Less optimum timing, within a few degrees of MBT, has a lesser effect on output. Just about all aircooled 911 road engines are knock limited and detuned for the factory fuel spec. Once you add this into the mix, the results are different. Porsche's response to the elimination of 5 star 98-100 octane fuel initially was to back off the compression ratio, as in your 8.5:1 example. After the oil embargo when fuel efficiency became an issue, epecially in advertising to sell new models, they changed direction and increased the compression ratio several times and backed off the timing . The increase efficiency from higher compression was more than worth the reduction in timing.
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Paul
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