A major benefit with the Elf fuel is/was that it met FIM criteria, and I have no doubt is more highly refined than something such as Optimax. Incidentally, I recall StephenRC45 playing with Optimax in 2-strokes on the dyno, and not quite getting the results that were expected! I'm sure he'll comment later.

Anyway, if you set up for a lower octane (eg. pump unleaded) fuel, and then run a higher octane like MITS42, at worst you may drop off a hp or two, as the two fuels will burn differently, and the setups should be optimised for each condition. However, it's far less likely to cause you problems than if you were to say set up for MITS, and then drop down to 97 super U/L. You'll almost certainly get major detonation going that way!

Setup for the lower octane, more commonly available fuel, would be my advice. You'll laugh, but Tescos are doing 100 octane pump fuel now, and Steve's 75hp MC21 F-III was thrashed by many on a number of track days last year on it, with no ill effects. It's legel, cheaper than AVGAS, and readily available... and minimum delivery is only £1!
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Andy.
NSR-WORLD.COM

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