STC for Rotax Engine to use Mix fuel to meet AKI 91

Their both approved by Rotax so go ahead. My guess would be you don’t need much Avgas to bring 87 up to 91.

A petroleum engineer could probably give you the ratio or you could error on the conservative side like 50/50.

Ed

In the US you don't need an STC (supplemental type certificate) to mix the 100LL and Auto fuel to get 91 Oct.. I see you live outside the US. Do you have to have one where you live?

Hi Ed,

You need at least a 50 / 50 blend to go from 87 to 91 by adding 100LL. Better to have a bit more 100LL than to be too little and possibly have an issue. This would be for the 100 HP+ engines. The 912UL 80 hp can use a fuel with a lesser octane. i.e. 89 or 87. Even then I personally prefer to use 91 oct. all the time.

The only information Rotax provides is the following statement found in service instructions: Selection of suitable operating fluids for ROTAX® Engine Type 916 i (Series), 915 i (Series), 912 i (Series), 912 and 914 (Series)

https://legacy.rotaxowner.com/si_tb_info/serviceinfo/si-912-016-r13.pdf

NOTICE: Any mixture of unapproved fuels and/or additives that cause lower than the specified octane rating can cause engine damage e.g. detonation.

The Stations around us have all reduced it to 90 octane. There are different definitions of octane?  I mix 10% or  more to be in the safe side.