The only thing better for your engine than 80 is unleaded mogas.
100 is poison.

R. Wubben wrote:

I am curious about a situation I haven't encountered before.

I just bought a '62 Cessna 172 with 70 hours on an overhauled 0-300
engine. New millenium cylinders were installed.

Can I, or should I, run on 80 octane or 100LL?

The airport that I'm moving to has 80 octane available (a rarity in
this day and age).

My previous airplane was a '59 Forney F-1 (Ercoupe) with a C-90 and
regular cylinders and I had two stuck exhaust valves in 2 years
despite aggresive leaning while running on 100LL (but not putting in
any Marvel Mystery Oil or AvBlend).

So, 80 or 100?
MMO or AvBlend or nothing? (does one need to mess with these if you
are running on 80?).

Thanks,
Ryan Wubben