leaded characteristics

during the "middle years" of the switch from leaded to unleaded... there were a few things that set the 2 apart... for example the filler neck is narrower for unleaded... and unleaded needs exhaust vavle seats... are there many more?

Cars with catalytic converters, (starting in 1975) needed unleaded. Also oxygen sensors require unleaded.

Some cars from the 60's to 1970 with very high compression run better on premium leaded gas. They will run on premium unleaded but still often require an octane booster for best performance.