To vac advance or not to vac advance

The more spark advance the better, for mileage, performance, and low emissions, until you reach the knock limit. That limit depends on gas quality, temperature, throttle position, altitude, and engine design (c.r., cam).

I like 1967 'cuda's comment (post #9). That makes a lot of sense, and I never thought of it before. You don't want it sparking before TDC since the engine will want to kick back and fight the starter. Better to retard the spark while cranking. I think some engines are designed like that (tractors, etc). Probably the Model T, so the owner didn't break his arm as often.