Supermouse
Avgas unlike Mogas is not tested on a RON (research octane number) engine, so you'll never see a RON rating quoted for Avgas. It would be however roughly 115 RON. The MON (motor octane number, different octane engine) of a 98 RON Mogas would be around 88 MON. So you can see that the anti detonation performance of the 2 fuels is vastly different. Avgas is made from higher octane blendstock to start with plus the addition of Tetra ethyl lead (TEL), an anti knock additive, produces the superior octane ratings. Avgas is also tested on a third type of engine, a boosted (supercharged) octane engine to give a rich rating performance number (PN) which is why Avgas is/ was quoted as Avgas 100/130 for example. (100 MON, 130 PN).
Trying operating an engine designed for Avgas on Mogas and it will destroy itself very rapidly.
I operated, installed, maintained, overhauled etc octane engines for 20 years so I guess I know what I'm on about..
Cheers
Octane