I've tired the DV formula on different engines and his adjusting duration, instead of changing lsa. It only works for carb engines in a narrow dispacement/rpm window. Not EFI friendly at all.
They say the formula is for 10.5:1 cr.. Reducing the duration alot to get the vaccum/idle puts the dynamic compression WAY Too High. Not to mention the duration would be so short that it wouldn't even make the power @ the desired rpm.
There are ALOT of factors that the 128 formula doesn't take into account. The overlap chart is useless.