[rotorwrench]

I remeber reading somewhere that the reason avgas had the broad ratings back in the day like 100/130 and 115/145 was to have an indicator of lead content versus mixture ratio. In some cases they were dealing with mixtures as lean as they could get on say a big 4360 or 3350 radial and the 115 would be the highest content for full best lean at high altitude and then 145 at full rich for take off. Most fuels that used lead were rated with a max content but they also had a minimum content so it could have a lot of TEL in there or a minimum quantity per gallon. I always figured the refiners used the minimum they could get away with for Ethyl Mogas since it wasn't making them any more money using the max. The only thing you ever see from the gas police is checking meters for accuracy. They do take samples now and then to test but you know how the government is.

I have an EPA document that mentioned the average TEL content in auto fuel was 2.4 grams per gallon prior to 1973 when they started the no lead process. I think this also includes premium fuels that were available at that time. 100LL by the ASTM has from 1.2 to 2 grams per gallon so they aren't that much different in TEL content from car gas circa 1972. I always wondered how well the stuff stays in supension though. If it sets in a tank a long time it might change the concentrations in the batch.