Denny,

I know we have differing ideas on vacuum advance; however, these are the instructions from a ZZ4 spec sheet, verbatum:
Set spark timing at 32 deg. before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32 deg. of total advance at wide open throttle (WOT). The HEI vacuum advance canister should be connected to a ported vacuum source (no vacuum at idle). The HEI distributor supplied with the ZZ4 engine has mechanical centrifugal and vacuum spark advance with the following curves:

Mechanical Advance:
1100 RPM 0.0
1600 RPM 12.0
2400 RPM 16.0
4600 RPM 22.0

Vacuum Advance:
2.00" 0.0
7.50" 20.0
Based on the 32 deg. at 4,000 RPM, and 22 deg. in the mechanical advance, the engine should drop back to about 10 deg. with no vacuum advance.

Now, that being said, from searching the ZZ4 discussion boards, I have found some indications that the GM HEI shipped with these crate engines doesn't have a really good curve. Too much vacuum and mechanical coming in too late. I found this thread particularly interesting:

http://www.sallee-chevrolet.com/Disc.../653/1607.html

You may convert me yet . . .