I know these topics have been discussed and Ive done a bunch of searching but couldn't come up with the answers Im looking for.

Im considering my fueling options. We have 100LL on the field but the price is quite high, almost $6. Im also weary that 25 hr oil changes are going to get old pretty quick. So long story short Id like to find an option that will at least give me 50 hr oil changes and not break the bank (max 30 - 50 % avgas use as I understand it). During cross country I plan on fueling with avgas as others do. Which means I should be using mostly non leaded gasoline all other times.

In our area we have 90 ethanol free car gas. Which I think is 90 AKI. My first question: Is this an option? I know the engine needs 91 AKI min, so is there a reliable way to mix avgas and 90 to get up to 91-93 to have some buffer? I could not find an AKI rating for 100ll and a good way to estimate the mix.

I did find this document https://www.rotax-owner.com/pdf/AvgasAutogasMixing.pdf from Rotax-owner which deals in MON and gives a rough way to estimate but does this method apply to other ratings? Also what is the min MON for rotax?


For those interested: I also got a quote from Swift for UL 94, 700 gallons per gallon cost delivered was $6.36. It was about $6.90 if only ordering 350 gallons. I did some rough calculations including oil changes (oil and oil filter cost me $70 with shipping from lockwood) at 25 hrs running 100 avgas and oil changes running 100% swift at 100 hrs. The cost per gallon used was almost a wash $6.50 per gallon with Swift and $6.60 per gallon with 100LL. This is independent of hrs run, it is adjusted for oil change cost per gallon. Assuming a 5 gallon per hr average.

So swift starts to sound like a decent option, likely better for the engine long term AND you save a ton of time in changing the oil. But it is pricey. Id love to be able to use local car gas and mix to 91-93 with Avgas. What would be even better is if that ratio was less than around 30% avgas, because then I believe 50 hr oil changes would be acceptable and the cost would be WAY cheaper.

So what is everyone doing? And is there a known and effective way to mix 100ll and 90 ethanol free?

Thanks!