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Paul,
You are right about the temperature.
Heywood says that detonation (knock) occurs when the energy released by the combustion is larger than the heat lost to the surrounding: pistons, cooling system, exhaust gases, water evaporation (if water injection is used). There exist a self-ignition temperature for any mixture.
However this is theory. In practice the heat transfers are complex. The faster you compress the mixture, the higher will be the final temperature (so run low RPM) because heat transfer to the cooling system does not grow as fast as RPM (heat transfer increases due to higher turbulences). With a very inefficient engine the heat losses will be higher during compression (so use overcooled engine). With a lot of friction work (at high RPM, say above 4000) a lot of heat will also come from pistons/liners (so use good oil, big clearances and short stroke).
The FI engines allow us splitting the compression work into 2 stages: inside the compressor and inside the liner. With the HUGE advantage being able to cool between these two stages. I think the best is to compress as much as possible (still being efficient) by the compressor, cool and than compress less by the piston, because after the piston work we can not cool any more, it's too late. From this point of view using low CR is better. This also gives us more control over the overall CR.
Another point is the pressure distribution inside the chamber. Often knock appears in particular regions of the chamber, the high pressure ones, because there the temperature is the highest. I'm not talking about autoignition due to hot points. Recent advanced simulations allowed designing very high CR chambers with very flat pressure distribution (at the end of compression). Of course hemi chambers are winners in this game.
Modern turbo engines run high CR to be efficient during cruising. And they use variable valve timing VVT systems which allow lowering the true CR in the FI mode.
std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm
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