Most aero engine makers other than Rotax have published similar documents to this one by Jabiru. Here is a Lycoming document:
http://www4.total.fr/germany/Lycoming Service Instruction 1070S.pdf
On the other side of the coin we have Peterson's mogas STCs for a wide range of Lycoming engines which people have been using successfully for years. Hundreds or thousands of RVs here are also using Mogas with no detonation issues.
For a very exhaustive fuel study go here:
http://www.crcao.org/reports/recent...k Tests of 30 Unleaded High-Octane Blends.pdf
A summation is on pages 72-73. It concludes that certain unleaded formulations were superior in knock resistance to 100LL while other formulations were inferior. High variability of formulation and performance was noted with the latter not necessarily explainable.
Much research was done on aviation fuels in the '40s and '50s. One of my old texts though shows that most formulations of basic gasoline stocks, Heptanes, Aromatics and Olefins have high lead susceptibility although within that group, octane increase per gram of lead can be variable up to 50%. Despite this, clearly, mixing 100LL with almost any unleaded gasoline formula will in fact increase octane noticeably.
Having run many turbocharged race engines on all sorts of different fuels that I mixed (even from scratch), I agree with the old texts. A bit of lead allowed measurably more boost to be run before encountering detonation on the dyno.
This contradicts some of what Jabiru says here. They are just playing it safe because they have no data- just use 100LL and you shouldn't have any detonation is the message. If we look at it from Jabiru's perspective rather than the operator trying to save some money, then they are probably right that diluting 100LL with Mogas will reduce the fuel octane rating and could lead to detonation under some circumstances..
What Lycoming and Jabiru are concerned about is the variability of mogas formulations and this point is very valid in my view and confirmed by the FAA tests I would say. They simply don't want to take responsibility for warranty claims resulting from detonation by using inferior auto fuels and I don't blame them.
Interestingly, the liquid cooled heads on the Rotax seem to give them better detonation resistance than their all air cooled brethren. Rotax generally recommends unleaded premium Mogas rather than 100LL which tends to leave deposits in chambers, on valves and pistons and the gearbox, requiring a halving of oil change intervals when running 100LL.
