Manifold Vacuum Experiment

I'll say this and it's indisputable. If there's only ONE reason to use manifold vacuum advance on the advance can, it's so you can run extra advance at idle without lugging against the starter. Since there's no vacuum on the can until the engine starts, it would be smart for bonified race engines with 12:1 and over to run a vacuum advance with manifold vacuum on the can. I've done it, in fact and it works quite well. Every bit as good as an ignition kill switch. Since the extra advance at idle has good benefits, especially on a lower compression engine, there seems to be no down side.