also, 100ll avgas is rated different. The ll=lowlead, but compared to most race fuels, it is actually high lead. Also, gas you see at the pump is rated as (R+M)/2, where as 100ll is just the motor octane I believe. 100ll avgas is actually quite a bit higher than a 100octane auto rating..... It's also "more" consistent than alot of the gas you buy at the local gas station.

I agree with Sax. 100ll is a higher rating compared to auto fuel as said before, its designed and rated at elevation where it is primarily consumed not at sea level. Stuff smells great though. :lolhit: Always loved smelling dads Bonanza idle by. :coolcowboy:

Pump gas octane numbers are "minimum" octane. I have tested 50 + brands and octanes within the brands. The octane in each case is 1.0 - 1.8 octane higher than what the pump says. 93 octane is really 94.5 for instance. I have also test 3 local potomac river marinas pumps each is 1.0 octane higher than what is written on the pump.
Ethanol remains 9.5 - 11.5%

This is true. 100LL would be around 105 on the (R+M)/2 measurement system. The Research number is usually around 10 points higher than the Motor number when they are around the 100 range.

Yes, that is the bottom line. No matter how many ratios, mixtures, & combinations you read or discuss, the piece of mind, and "cheap insurance" you're paying for by having higher octane, is priceless to me.

Our marina carries 87 octane, & 110 octane at the pump for us. My engines are allegedly set to run 93 octane, but since day one, I've been running straight 110 octane through them. I haven't experienced any loss of power, or any other fuel related problems from running straight 110 octane race fuel. When I've been out of town with the boat, I have mixed 91 into the 110 that was already in the tank without any issues, since the mixture was still safely over the required amount of octane they needed.

I found out the hard way on a boat I owned years ago, that its motors required 95+ octane fuel, after they BOTH detonated. Since I didn't know this, I had been burning 93 octane fuel. All it took was roughly a 2 octane deficiency to smoke them both. Ever since then, I've tried to have a little higher octane fuel in any engines I've had, just to be sure.

When I'm on another lake, I'm always a little leery about pumps on the water, just because you never know how much of a specific fuel, especially premium, they are actually selling. If the marina is seasonal, and they don't typically sell enough premium fuel to require their tanks to be refilled with fresh fuel very often, it's tough to know how long the fuel has been sitting in their tank. Or, you never know what's been added to their fuel, like octane boosters, stabilizers, etc. The actual octane of the fuel they are refilling the "93 octane" pump with is also a concern, since it could be 87 octane that the marina is selling as 93.