Re: Hei distributor advance mechanical and Vacuum
I have them for the vacuum advances. Best thing in the vacuum advance issue is to go with a Crane full kit, all the 20 different stock settings, and everything in between them.
Until the ZZ crate engines came about, the various divisions did their own weights, center, start/stop, curve settings by varying the weights and center combinations. When we designed and developed the large HEI, we made the basic parts large enough to use a lot of different mechanical advance curves, with ONE basic floor plan, so it would be easy to swap weights/center/springs to match the various emissions curves for all GM engines of the time. We even designed them to be placed one face up for right hand rotation distributors, the other face up, to work with left hand rotation distributors. They were even modified to have no mechanical/vacuum advances for EFI distributors.
There were a very few late 1970's/early 1980's Chevrolet small and big blocks in things like trucks, Suburbans that used the 41/375 combo, that is basically where the ZZ curves came from in the first place.
Some have taken it upon themselves to plot and record curves for various combinations, but the amount barely breaks the surface of what is out there.
The most popular is the ZZ combo, weights 41, center 375, but the ZZ is sprung so tight that the curve doesn't start until about 1,400/1,500 rpms, so, change the springs to get start near 800 or so, limit at or near 2,900 to 3,200 rpms. With that combo, you will attain 22 crankshaft degrees of mechanical advance, and if added to say, 12 initial, total will be 34, 14 initial, total would be 36.
Now, some might have combos recorded to use less mechanical advance, as the various kits give, but wider applications, and they can be beneficial, but don't get too much initial over mechanical, supplement a more conservative initial with a correctly set vacuum advance degrees, and the engine will run great.
ZZ vacuum advance is marked 69120, good for moderate vacuum levels for stock to fairly moderate engine vacuums, only needs the Crane plate mounted on the one side of the vacuum advance pull pin I recommend placing it, not the Crane method. There are a few people here that have done the mods, I am sure they would confirm good results. The vacuum advance modifications allow you to use full manifold vacuum to supplement the initial timing, bringing the idle timing to between 22 and 24 deg/BTDC, just where the engine likes it.
So, yes, I do have the vacuum advance info, thank you for offering it to me.