100LL aviation fuel (AvGas) serves as the primary high-octane fuel for turbocharged aircraft piston engines and is also suitable for use in smaller, naturally aspirated engines.
You can run AvGas in your 2-stroke outboard engine. 100LL AvGas has a similar lead content, distillation curve, and specific gravity to some racing fuels. Many use blends with pump gas to get to the right octane rating.
First, your baseline must be correct and we understand which octane rating is being used for your specific fuel.
In the U.S., we use the average of RON plus MON, also known as AKI, (or RON+MON / 2 = AKI). This equals the minimum octane rating for unleaded motor fuels and is the number you see at the pump at your local gas station.
In the example pictured, we are using aviation fuels, since this is a common and affordable way to increase the octane of pump gas by blending.
Here you can see, for example, 100LL AV GAS is the equivalent of 105 AKI, so a 50/50 blend with 91 from the pump gets you 98 AKI octane (105 + 91 / 2 = 98).
In Europe (EU), the octane rating on the pump is simply the RON figure. EU 95 octane = US 91 octane and EU 98 octane = US 93 octane.
You can apply this simple math to any fuel once you know the octane rating method.
You might be able to find a local airport to buy 100LL fuel. Be sure to bring your 5-gallon jugs or some may allow you to pull in your boat. https://www.airnav.com/fuel/local.html
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