I may be completely off here, but it also seems that manifold plenum size (along with runner volume) would affect vacuum. As in, the smaller the plenum, the higher the vacuum (all else being equal). If I'm right, I guess this is at least part of the reason why excessively big intake plenums tend to give soggy response with carburetors.

Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."