Vacuum advance

Bewy said
To Dartfreak 75.

The only difference between PVA & MVA is that MVA is operating at idle, PVA is not.
I suspect your engine will benefit from MVA. Easy to tell. Hook it up! If idle rpm increases & idle is smoother, then the engine likes it. It may not want all of the available advance that the VA can can deliver, so a stop would need to be fabricated to limit the total VA.
The difference between a locked dist providing, say, 34* at idle & MVA giving 34* is that the engine is always going to see 34* with a locked dist, which might produce pinging. MVA is load sensitive, so the 34* will reduce to a lower number under load.

You would be surprised how much extra idling timing even stock engines like.
Example: Pontiacs idled with 26*, 6* init + 20* MVA. These were high comp engines [ 10.75 ] with mild cams. Lower CR, more cam duration, needs more idle/cruise timing.
What is different between a Pontiac & a Mopar? They are made of cast iron & ingest fuel & air.

I just saw this post thanks for sharing. That makes more sense than anything iv read before and I completely agree. I was using 318willruns method of timing setting, basically he just keeps bumping up his timing at idle till the idle no longer increases or it stops idling smooth. Then backs it off 2 to 4 degrees which landed me at 20 degrees. I got all the way up to 24 degrees before it stopped increasing. And it seemed to run really good there. So using MVA I could set my initial at lets say 10* intial and using mva id be back at 24* during idle. Until the engine is under load. I guess im just gonna have to play around with it different ways and see what my engine likes. I appreciate all the help I have a much better understanding of the difference now!