Sorry, another brain malfunction, I have 29 degrees total not 39. The heart shaped SD combustion chambers allow for a few degrees less timing but mine was quite a few less. The guys running the dyno were surprised but that's what got us the best power. So the mechanical advance is only 20 degrees. With my number 48 iron heads I ran 41` total and 12 initial for 29 degrees mechanical and vacuum. I have a different distributor than I had with the iron heads and have yet to measure with the vacuum attached.