http://bmwmotorcycletech.info/valves.htm
About 3 or 4 ounces of aviation leaded gasoline, in the commonly available grade called 100LL (100 octane Low Lead) is needed per gallon of UNleaded car gas, for good protection on the 1979 and earlier airheads. On a practical basis, less than this amount seems OK, and many have had good results by simply adding a cupful (a cup is 8 ounces officially, but in practice is 5-8 ounces) every few tank fillups. NOTE that this usage for road vehicles is illegal in the U.S. Still, many who have lawnmowers, etc., with old type seats, add a small amount of aviation fuel to their tanks.
For those wishing more exacting information, aviation fuels containing either 4 or 8 grams of tetraethyl lead per gallon are, or were, common. Leaded fuel for airplanes was typically available in 87 octane, and low and high leaded 100 octane. Today, only 100LL is likely to be found at airports. It is commonly accepted that approximately 0.1 gram (some say up to 0.3 for high protection) of tetraethyl lead per gallon is enough to provide reasonable valve seat protection. This is FAR LESS than the amount required to boost octane any appreciable amount. Using the 4 gm/gal specification type of aviation gas (100 LL), only .025 gallon of aviation gas is needed per gallon of unleaded car gas. A gallon is 128 ounces (U.S. measure). Thus, only 3-1/4th ounces of aviation gas per gallon of unleaded car gas is required for acceptable protection. Frankly, less is needed, as aviation piston engines normally work very much harder than our airheads.
For those wishing more exacting information, aviation fuels containing either 4 or 8 grams of tetraethyl lead per gallon are, or were, common. Leaded fuel for airplanes was typically available in 87 octane, and low and high leaded 100 octane. Today, only 100LL is likely to be found at airports. It is commonly accepted that approximately 0.1 gram (some say up to 0.3 for high protection) of tetraethyl lead per gallon is enough to provide reasonable valve seat protection. This is FAR LESS than the amount required to boost octane any appreciable amount. Using the 4 gm/gal specification type of aviation gas (100 LL), only .025 gallon of aviation gas is needed per gallon of unleaded car gas. A gallon is 128 ounces (U.S. measure). Thus, only 3-1/4th ounces of aviation gas per gallon of unleaded car gas is required for acceptable protection. Frankly, less is needed, as aviation piston engines normally work very much harder than our airheads.
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