I don't remember the first year in which new vehicals required unleaded gasoline, but that year and thereafter the engines necessarily required hardened valves and valve seats. Now, when engines manufactured prior to that time are rebuilt, I assume it is common practice to install hardened valves and valve seats to prevent burning.
Valve clearance specifications for those older engines allowed sufficient clearance to prevent burning even with leaded gasoline. The specs for my 1960 235ci calls for .006in for intake, and .018in for exhaust. Even with rebuilt rockers, the exhaust valves are somewhat noisey with the .018 setting. My question is this: has anybody researched/experimented with less clearance for the exhaust?
It would seem that somewhat less clearance could be tolerated now that we have hardened valves and valve seats.
meansam

1960 Chevy Stepside