RR,
MVA has it's benefits...........................PVA is useless & we got it because of emissions [ like lower comp ratios that made engines inefficient ]; engines that used PVA had MVA in the background to come to the rescue & MVA do so until the end of the carb era.
There are some combos that will not benefit from MVA......buuuuuuuuuuut there are very few.
MVA is not a crutch, no more so than using higher ratio rockers to increase HP. The engine needs a certain amount of ign timing advance at idle for best power & MVA is one method of achieving it. Another method would be a locked dist. However, this method may cause detonation because the timing is no longer load sensitive; it is load sensitive with MVA.
The problem with MVA is that there is no procedure [ that I have seen ] to dial it in.
The instructions that come with the adj VA units such as Crane, Accel, Mr. Gasket etc are written by people who are clueless to what MVA was designed to do.
D. Vizard reviewed the then new Crane Elec Dist in Nov 04 of PHR magazine; note that Crane went to the expense of adding VA curves, not just centri curves.....
" At idle & low speed operation, the amount of advance reqd to most efficiently utilize the air & fuel entering the engine can be as much as 50-55*. This is handled by the vac adv: a function many hot rodders believe is not needed because their favorite drag racer does not use it. Now is the time to listen & listen up good. A functional VA is the single most effective camshaft tamer you can get...."
And closer to home, Mopar related, MM magazine Ovt 2015:
" The initial timing went from 15 to 26* while adding an inch of vacuum. Total timing didn't change, but a dramatic gain in low rpm throttle response was realized. If tweaked correctly, you'll see your idle vacuum creep up, as we did here."
