What does your training materials say about tuning 500 inches, big cams, open plenum intakes, Dominator carbs, straight through exhaust, etc, etc? Good info to know, but not necessarily pertinent. Chrysler engineers had to make many, many compromises to accommodate every idiot with a payment book. Not necessarily what was best for the engine or even for peak performance at the time. Let alone half a century later.

This is a discussion of semantics. Retarding vs dropping out. Maybe the same thing, but to say that the vacuum advance retards timing could be confusing for those that are not as familiar with the function. To describe the vacuum can's function as advancing and dropping out that advance is just more explanatory. Saying that the vacuum can advances and retards the timing could lead someone to believe that it could take the timing both above and below the mechanical timing. It may be technically correct, but is not as clear.

With all the mods going on with our cars, it is possible that some unique combos, particularly drag cars, could benefit from manifold vacuum. But for most street combos, dialing in the distributor and adding a tuned vacuum advance with ported vacuum is the way to go.