Quote:
Originally Posted by Old Tele man
OCTANE is a benefit if/when you can dynamically increase (ie: turbocharging) the engines' compression ratio so as to USE its higher knock resistance; otherwise, it's simply a GOOD thing that can NOT be used.
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Not entirely true. The effective compression depends on the precise point in the compression/expansion stroke at which the spark ignites the fuel. So if your car is built so that at TDC it has 10:1 compression, a few degrees after it'll be 9.5:1, a few degrees later 9:1, etc.
I believe (though I don't claim to be an expert) that this is how most engines are designed these days. They have a higher built-in compression than would work with the octane of regular gas, and anti-knock sensors adjust the ignition timing so that it is running just on the edge of knock.