-=> Quoting Alexander Bilan to Tom Collins <=-
 AB> This is the only issue which I would add to the experimental list.
 AB> Manifold vacuum is/was the source of choice for hot rodding.
That is completely incorrect. Any engine will have it's own requirements
in hot rodding or otherwise applications. The ONLY TIME I have ever seen
an advantage to straight manifold vacuum is when an engine is very
cold and just started.
For pure hot rodding, no vaccum advance is used very often. Also some
heavy duty and truck applications use no vacuum advance.
I have seen several engines with a vacuum retard.
 AB> Heres one to contemplate for the manifold/ported vacuum debate:
 AB> Travelling uphill, you open throttle to maintain speed; manifold
 AB> vaccum drops, ported increases.  Hooked to manifold you reduce vacuum
 AB> advance and consequently reduce the chances for pinging.  Hooked to a
 AB> ported source, you might induce a pinging due to the vacuum advance
 AB> remaining fully advanced.
Ported vaccum will not exceed manifold vaccum. If you open the throttle going
up a hill, the ported and manifold vacuum will both drop just the same.
WHY? Because ported and manifold are the same except in a closed throttle
position, at which point port is robbed of vacuum by the throttle plate.
At any position a little beyond closed throttle, they are always the same.
--- Blue Wave/Max v2.12 [NR]
---------------