Creamie,
I will chime in and and say that tetra-ethyl lead performs a number of functions, one of which is the raise the octane rating.
I am told that Continental (possibly Lycoming, anybody know for certain??) have been producing cylinder kits where the specification of the exhaust valve and valve seat have been changed to prevent accelerated damage to same,( ie; using unleaded in an engine designed for leaded fuel) so that unleaded fuel can be used, if you have a "mogas" STC for your aircraft.
There are quite a few engines that were certified originally for 80/87, I have a pair that were originally certified for the little known 92, with suitable valve/seat changes, these should be able to operate on (motor octane number) 100 unleaded.
All the early Gipsy engines had a wonderful fuel specification:" a good grade of motor spirit, well filtered", back in the days when "hi-octane" meant 60.
Tootle pip!!