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Curious about 100LL and Magneto Timing ...

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Well-Known Member
Apr 9, 2010
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This is just a general question about a topic I don't understand fully and can't seem to find a lot of information on.

I've seen passing comments regarding the fact that the engine timing (25deg from TDC on my O-320, IIRC) is related to octane, or some other characteristics of the fuel, and that some people seem to think, and/or actually do, retard their spark to say 24deg when using 100LL instead of the original 80/87 fuel that the specs were done against I guess.

Could anyone enlighten me, and any one else reading, on the theory and practice behind this? Or maybe have links to resources that explain this?

If it is so, why isn't it the standard practice/common knowledge (to adjust timing differently I mean)?


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