thanks, mark.
if an engine is built to have high compression it requires a higher octane fuel. low octane fuel will ignite under compression prior to spark in a high compression engine and that is what is referred to as "knock". lead prevented the valve seat erosion . hot valves would stick to the head and as it opened it pulled off small bits of the valve seat and that brought on recession of the seat. with the removal of lead there was a reason to use hardened valve seats. that’s why I use the lead additive and there are many brands. it works ok for me. ethanol is an octane booster. that’s why the refineries use a sub grade gas (84 or 85) to blend with ethanol to get an 87. they use an 87 with the ethanol to blend the 92 or 93.
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