Bruce ( Shrinker )

Greg,
Thanks for the comments. While I could find plenty of comments from people on MVA more knowledgeable than me, I think David Vizard's comment in the Nov 04 issue of Pop Hot Rod magazine takes the cake:

' At idle & low speed operation, the amount of advance reqd to most effectively to utilize the air & fuel entering the engine can be as much as 50-55 degrees. this is handled by the vac adv: a function many hot rodders believe is not needed because their favorite drag racer does not use it. Now is the timer to listen up & listen up good. A functional vac adv is the single most effective camshaft tamer you can get. By taking the time to hook up the vac adv to a manifold vacuum source you can get a big cam to idle as it it were about 20* less than it really is. Conversely, if you are looking for a decent idle the use of vac adv will allow you to use a cam of, at the very least, 5* more duration/overlap than would otherwise be the case.'
[ Italics are mine ]