Vacuum advance information and myths
As far as what a factory 383 or 440 4bbl likes, the factory spent quite a bit of time working out timing curves to maximize power and economy. We can check out the acceptable range of mechanical timing and vacuum advance in the 1967 and older service manuals.
I've posted a number these on FABO.
For example 1967 383 standard 2bbl and 4 bbl from the Plymouth FSM plots outs like this
Next one is the average vacuum advance rather than the acceptable range just to make it easier to work with.
Knowing the cruise rpm and cruise vacuum the timing can be figured out.
I think its safe to say that unless the car hits real high wind resistance, at highway speeds and rpm the vacuum on flat road will be above 15"Hg in most cases.
A more general baseline can be had from the older Direct Connection /Mopar Performance guidelines that I posted in the vacuum advance how to.
Idle is surprisingly high load, and before emissions concerns, fairly rich. The engine is producing very little torque at 500 or even 600 rpm. A percentage of that goes to overcoming friction. So best to think of it as a high load, somewhat rich and dense situation.
As far as what a factory 383 or 440 4bbl likes, the factory spent quite a bit of time working out timing curves to maximize power and economy. We can check out the acceptable range of mechanical timing and vacuum advance in the 1967 and older service manuals.
I've posted a number these on FABO.
For example 1967 383 standard 2bbl and 4 bbl from the Plymouth FSM plots outs like this
Next one is the average vacuum advance rather than the acceptable range just to make it easier to work with.
Knowing the cruise rpm and cruise vacuum the timing can be figured out.
I think its safe to say that unless the car hits real high wind resistance, at highway speeds and rpm the vacuum on flat road will be above 15"Hg in most cases.
A more general baseline can be had from the older Direct Connection /Mopar Performance guidelines that I posted in the vacuum advance how to.