I guess the way I see it is if you have an engine that starts fine with the static advance setting and it idles good, then ported vacuum is the way to go. If you have an engine that idles good with more advance than allows for starting with out kickback, then manifold vacuum is the better one since you can retard the timing to allow it to start and then have it advance a set # of degrees with the vacuum to where it idles good. So at WOT, both manifold and ported vacuum signal will drop significantly and mechanical advance takes over at that point correct? Sorry for all the questions, just trying to educate myself on this subject
Pretty much
Some cams like more timing at idle. This raises the idle speed, giving you enough room to close the throttle blades so it will idle on the idle circuit. Some don't.
To do this, you can:
use ported vacuum
crank up the initial timing, and limit the total timing.
But, like you mentioned, you might run into kickback issues.
Or,
use manifold vacuum
a more reasonable initial timing (maybe still limiting the total),
And have the base timing jump to initial + vac advance once it starts.
Once the throttle is open past idle, both manifold and ported are the same. At wot, both are near zero so there is no advance added. The only difference is at idle with the throttle closed.
