Avgas traditionally was available as 80/87 (red), and 100/130, (green), both contained tetra-ethyl lead as antiknock agents. Early Aviation motors were carbureted, and leaning was manually adjusted. Full “rich” was used for high power segments, takeoff (& landing in case of a go-around). Once at cruise,the engines were manually leaned for better fuel economy. Before the days of digital monitoring, a simple EGT, (exhaust gas temp), gauge was used, with a single probe on the hottest cylinder.
Engines were run slightly richer than stochiometric, (most efficient), for longevity. Lots of old wives tales persisted in leaning at night by watching the color of the exhaust tubes…a good way to shorten engine life. The two numbers closely equal the knock index at full lean/full rich settings. 80/87 was for lower compression av engines.
Many believe aviation gas is “hi-test”, & much more “powerful” than mo-gas. In fact avgas has lower Reid vapour pressure than mo-gas. It has to be less volatile to prevent vapour lock at the reduced atmospheric pressure experienced at high altitude.
I be,ieve it is very hard to find 80/87 today. One of my 1st flying jobs, I burned quite a bit of it in ‘71 GMC 1/2 ton, (350 4 bbl Rochester carb), and it ran fine.
Todays 100LL (blue), is the most common today. LL stands for low lead, however It still contains lead, acrually about equal to 70’s mo-gas. 100LL should run fine. The biggest caveat of avgas is lead fouls up catalytic converters, which is probably not an issue on a marine application. It’s also quite expensive vs mo-gas.
