Posted by Chris Jordan on October 16, 1999 at 10:55:48:
In Reply to: Vaccum Advance Distributor Question posted by Henry Jacobs on October 15, 1999 at 15:59:26:
In a vacuum advanced distributor, the spark is
advanced based (at least partially) on increasing
manifold vacuum.
In a centrifugal advance distributor it's strictly
rpm.
As Henry mentioned, advance based on rpm is
blind to load: you're approaching a hill and
your timing is happily moderately advanced based
on your rpm, but as you begin to climb your
rpms don't go up, so you don't get any more
advance.
In a vacuum advanced distributor, the engine would
begin to work a little harder up hill, draw a
little more manifold vacuum and advance the spark
some.
Aren't most (all?) vacuum advanced distributors
really vacuum AND centrifugallly advanced?