I'll just put a quick caveat in. Light a/c engines are so gash that you are unlikely to cause detonation in your normal bog standard O-320. Turbo'd and supercharged engines are a different matter however. We all need to be aware of it because if it does happen, then it can be a very expensive issue!
I'll put an explanation of how the octane ratings are worked out if anybody is remotely interested.
In aviation fuels, the different octane numbers are known as the Lean and Rich ratings, but they have different meanings. Any number above 100 is not an octane number, but a performance number.
The lean mixture rating is an octane rating and it is worked out in the same way as Motor Octane but converted by means of a table. There is very little difference between motor no.s and octane no.s.
The rich mixture rating is a performance number worked out using a supercharged engine and allows us to work out the mixture strength and boost for a specific light knocking setting. The Performance Number indicates the maximum knock-free power obtainable from a fuel compared to iso-octane.(A specific specially distilled fuel that acts as a control) The performance number is always higher than the octane number. The rich rating is an arbitrary figure that has been derived from decades old data.
Interestingly when 100LL was first introduced there were a large number of incidents of plug fouling, over heating and cylinder head cracking. It was so bad that 80/87 had to temporarily re-introduced. It was due to the reduced lead content of the new fuel. (0.53mlTEL/L compared to 1.06mlTEL/L.)
100LL is a different fuel from 100/130 and is it's own designator as well as octane number. It does not have a Rich mixture rating as such and was designed to replace 80/87 AND 100/130.
If anybody is still awake then I hope this may come in useful one day. (Not sure how, but you never know!)