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.
Ok, Chrysler engineers just did things for idiots??? What does that even mean? It is not my semantics, it is the words the Chrysler engineer used. Yes the vacuum can reduce timing certainly below the mechanical. You are in the Racers forum, I think they can understand what was said.
My only point was this is a total integrated product. Too many variables can be changed and folks don't always recognize how they have changed the SLOPE of the timing curve when you add a vacuum can. You seem to be trying to simplify the solution.
In general, springs are linear. With an inflection point as the heavy spring is applied when the loop closes up. You can control when they apply, and rate of advance with a spring change and total amount of mech adv by cam stop plate. Without a vac can you move up and down that timing line based purely on RPM.
With vacuum can it is not just moving further up the line, you now have a variable slope depending on acceleration or deacceleration and load. Your RPM timing is now different under different conditions because vacuum adv may be going lower or higher depending on load.
For a street car you need a device that can advance timing more then the car can handle when under WOT and full load. You don't want 55 total timing at WOT and your not efficient at cruise with 34. And yes and engine is an engine. The principles and engineering laws have not changed because displacement increased and a cam was added. Principles are the same.
It is more pertinent to discuss the use of the car rather then the size of the motor. Street, Strip or both. Yes, no (unless solving a problem), yes (maybe). There is a ton of cars out there running no vacuum or running plugged. The car will still run and perform.
