As far as I know, no high performance aviation engine will run low octane reliably without lowering the compression. Detonation and pre-ignition will occur. Also, Mogas contains ethanol which freezes at low temperatures up high and can cause fuel blockages. This is why 100LL has had such an extended stay despite it's unfriendly environmental footprint. However, it's coming to it's end, so a replacement is needed very soon.