Factory Small Block Heads

I will say, on an "almost complete stock" 360, going from 360 heads (as cast) to OOTB speedmaster heads, the et dropped about 2 tenths if I recall correctly. I think half of a tenth would be in the weight difference. So, only about 1.5 tenths in actual performance. Obviously, the cam wasn't designed to take advantage of the SM heads, but still it's what the track showed in that circumstance.