Perhaps a more useful comparison would be how much
lead is/was in 80/87 vs 100LL?

Those of use with older, low compression engines that were designed
to run on 80/87 may be introducing 4 times the amount of lead into our
combustion chambers by running 100LL than the original designers had
intended for.

80/87 has a maximum of 0.5 grams of lead per US gallon while 100LL has
a maximum of 2.0 grams of lead per US gallon. Unleaded Mogas is...
well... Unleaded!

In reading about this somewhere (AvWeb? EAA?) I recall words to the
effect that the refineries can get up to about 97 octane without any
lead, and they only add as much in to get to (or slightly exceed) the
100 octane rating.

I have the EAA Mogas STC for my C-170B, and the paperwork states if
you mix a certain amount of 100LL with unleaded Mogas (25% to 75%),
you get approximately the same amount of lead as you would have had
with a tank-full of 80/87.

For what it's worth, my O-300 absolutely *hates* straight 100LL (way
too much lead). Aggressive leaning, both on the ground and in the
air, can extend the time between fouled pugs and stuck valves, but
both are virtually inevitable without a lead scavenging agent (like
TCP) or using Marvel Mystery Oil, etc.

I burn Mogas on local flights and when/where I can get it on cross
country flights. When I have to fuel up with straight 100LL, I add
TCP.

Not only is the Mogas cheaper, I no longer have to worry about
fouled plugs and stuck valves! (aka a "no-brainer"). 8^)

Bela P. Havasreti