If I recall correctly, ethanol needed to be added at around a 10% level to prevent engine knocking. At its peak, lead was present at around 1.1 grams per gallo

If I recall correctly, ethanol needed to be added at around a 10% level to prevent engine knocking. At its peak, lead was present at around 1.1 grams per gallon, so about 0.1%. Not intended to excuse them. The amount of additive required was why leaded gas was cheaper than using ethanol. And as a reason, three generations grew up with lead poisoning.