V-12 ignition system upgrade

[MontanaDiver]

My old distributor had been modified and the led wheel had been riveted back on. I went with the SNG system and after solving an issue with rotors getting too warm, I am happy with the distributor. In retrospect, I would have ordered the Non-North American distributor to get vacuum advance instead of the vacuum retard unit. This would require a ported vacuum source instead of the manifold vacuum that the original source.

[MarekH]

A retard unit needs the exact opposite of ported vacuum - ported vacuum gives no vacuum signal when the throttle is shut but a retard unit wants a signal only with a closed throttle and it wants to drop that signal as soon as the throttle opens. On the original setup, this came from the bottom of the left rear carburettor.

Ported vacuum is just a subset of manifold vacuum. The only reason I think people tout it as "better" than manifold vacuum for ignition advance will be that the amount of advance cuts in more sharply when moving off from a closed throttle, so the impression will be of more acceleration. In reality, you can get that just by opening the throttle more anyway. At idle, your engine will be more retarded and generate more heat than if manifold vacuum were used. Other than that, it'd provide more engine braking when coasting. Once the throttle is sufficiently open, ported vacuum equals manifold vacuum and at full throttle, they both tail off anyway.

kind regards
Marek