I feel I must address a common misconception regarding octane. A high octane rating is a measure of the fuel's ability to resist knock/ preignition/ detonation. That having been said, a higher octane rating will burn slower than a lower rating, and this is accomplished by having a lower volitility than the lower octane rating.

So,

High octane = lower volitility and higher knock/ preignition/ detonation threshold.
Low octane = higher volitility and lower knock/ preignition/ detonation threshold.

AvGas is 100 octane, which would be fine in a modern engine, but since it has trace ammounts of lead, will foul the plug.