@DaveRS23, everyone...

Originally Posted by DaveRS23
...The only thing that I might have a little different experience with is the initial; the bumpier the cam, the more initial they typically like. All the way to locked out if it doesn't hit the starter too much when cranking...

So for the record, I am of the same opinion you are, that being: choose carefully, the individual components have to 'interlock/complement' each other, and that's not just parts fitting but equally important to their configuration. No matter how "esteemed" the author of a particular publication/book is, he/she may simply not have had the required experience with MY particular combo for their recommendations to be valid.

Having said that, I've been thinking about the manifold vacum option recently and simply ran out of time this past season to try it out. The reason being: I've done pretty much everything I could to make the carb ported option work, and because of the cam (hydraulic roller, 240/248 @0.050") I simply need to run more advance at idle. But as you stated above, when dealing with the limitations of the mechanical setups you eventually run into the brick wall: can NOT give it more INITIAL advance b/c the started will kick back.

In my current setup (W2 408 stroker, 10:1 static CR, 195 psi cranking, 91 octane pump gas) I use 21 deg initial, followed by a fairly quick curve with additional 15 deg all in by 2000 RPM, with the final 15 deg for cruising purposes. The 4K stall converter and 4.10 gearing helps with this on my street ride (engine does not really see much load that would cause it to labour at low RPM thus promoting detonation).

However, that's still not enough because for testing purposes bumping up the INITIAL to around 25-26 nets me an even steadier burn, and it's not even the 'smooth idle' that I'm after here, rather it is the more complete burn of the mixture (the sniff test and AFR tell that story).

So the theory at least is that by running off of manifold vac signal I may be able to:

1) keep the INITIAL mechanical advance low enough to prevent the started kick back
2) immediately bump up the idle & off idle advance to around that 25-28 mark where my combo seems to like it most
3) as soon as I get on it (we are talking cruising here, not WOT) the drop in the manifold vac signal is countered by mechanical advance coming in pretty quickly

#3 may in fact be controlled a bit more so as not to rely on the mechanical taking over all the ignition advance chores, after all there is a certain amount of adjustability in the vac can to either bring it in earlier or later, too bad you can't control the amount of the advance itself...lol

Anyways...worth a try, and that's probably going to be my first spring time experiment.

BTW: all of the above tuning could be eliminated by running one of the newer eletronic distributors where you can program the curve, that thought has certainly crossed my mind, but the prices on these units are still steep so in the meantime I'm relying on my Mallory YH Advance distributor that provides a fairly comfortable & quick adjustability (this is the mechanical advance setup that MP went to in later years - Mallory has a nifty spring tuning kit that provides a good mix of advance springs).

So to @carnut68: there are ways to make manifold vac work, but it's not a 'black or white' kind of a thing!