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Not necessarily Posted by Ari [Email] ![]() ![]() In Reply to: Re: Octane vs. altitude, Simon S, Fri, 5 Jun 2009 15:41:27 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Yes, most modern cars have control over timing. Retarding timing can prevent knock.
However, the control systems only have so much authority - they can't keep retarding the timing until the engine no longer knocks - at some point the engine no longer runs (where it doesn't knock, I guess.) So even with modern knock-avoidance systems, there is a minimum octane.
The same goes on the high octane end. The control system doesn't keep advancing the timing until it senses knock - running higher octane than necessary doesn't provide more performance.
So at high altitude with a N/A engine, you can run lower octane without knock. Just like at sea level, running higher than necessary octane provides no additional power. And at higher altitude, the N/A engine has less power because the effective compression ratio is lower; no amount of ignition timing twiddling will help with that.
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