Just though I'd pass this info along; it may or may not be applicable to your setup. It's just one more data point.

I posted last week that I was having some slight pinging when mashing the accelerator from cruise (2200 RPM, 4th gear). I was wondering if the vacuum advance had anything to do with the pinging.

Well, I disconnected the vacuum advance and went for a test drive, and the result was no pinging.

My conclusion is that the vacuum advance does not act instantaneously...even if the vacuum signal drops to 0 when the throttle is wide open, it appears as though it takes a second or two for the vacuum advance to return to 0.

FYI. If anybody has other thoughts, or similar experiences, please let me know.

As I've just spent the better part of a month playing with advance, distributors and ignition systems... here's what I know about a stock vacuum advance:

Though rated at 15-20"Hg. The diaphram in an advance unit I tested began to move at only 7"Hg and was fully engaged at 12"Hg as tested with a reliable, leak tested Snap-On vacuum pump. What the vacuum is released from the unit (during testing, of course) the spring SNAPs the rod back to the original static position. There is no bleeding or drifting. My unit as tested had an exact and immediate response to negative pressure, as applied.

Nothing happens instantly

3000 RPM / 60 seconds= 50 RPS
Crank takes 2 revolutions to fire piston

25 fires per second * 8 cylinder = 200 cylinder fires per second

Let’s say it takes 250 ms (1/4) second for the advance to return
That’s still 50 cylinder fires while it is coming off of the advance.
Ping Ping

Vacuum sdvance works with vacuum, period. No vacuum, no advance. What may have been happening is a couple of inches of vacuum at WOT, because the carb is too small. MANY factors can produce the results you experienced.

It might be expected, but it can not be tolerated.

That is probably why a lot of rodders run without the vacuum advance.

I will put in my 2 cents worth here. The amount that you will save if anything will be like driving to the next town to save a penny a gallon on gas. Especially on performance orianted engines.
Back in the early years of EPA envolvemnt in the industry we had many complaints of no power, poor milage, etc.
We recalibrated the carburator and the distributor, timed the total advance and put a ball bearing in the vacume hose so that it looked functional. Most of the people were pleased with the cars after the 'tune up'. Some you could never please. There are those that no matter what you can't please like the ones that want to pull a trailer 70 MPH and still get 20 MPG.
You don't see many HP distributors with a vac adv.

If you are getting a one or two hit rattle just as you hit the throttle, and then it goes away, you probably have a combination problem that involves the vacuum advance and the accellerator pump. Usually, if you disconnect the vacuum advance and it goes away, you can make it better by making sure everything is moving well and the vacuum line is big enough to drop the cannister quickly. Often though, the real problem is that the engine runs momentarily lean until the main metering system catches up. Not lean enough to cause a sag, but lean enough to detonate if you are close to it anyway, with compression or fuel quality. A touch more pump shot, or bringing the shot on a touch earlier in the throttle motion may take the detonation out even with the vacuum advance in place.

The other thing that I have seen is that engines running on the modern fuels, with hot ignitions, and particularly if they have high quench, seem to require a bit less advance, especially under light load. The days of having 50 degrees total at cruise appear to be gone, and low 40's seem to work a lot better from an economy, and tip in performance standpoint. This is based on having a total mechanical of the old standard 35 degrees (which may also need to be backed off by a couple).

I like to run a vacuum advance for the economy and the fact that at cruise it will keep the insides of the engine cleaner with less carbon buildup.

Some people put 5000 Miles + a year on.
Not race motors just a nice street motor.
I will take the extra 2 -3 mpg my vacuum advance is giving me.

Good points Booster.

Also engine temp/incoming air temp
Not easily controlled but you do notice the hotter the engine temp the easer it pings

i know Crane used to sell an adjustable vacuum canister for the OE Mopar distributors.
ive used a few in the past and had pretty good luck with them. i dont know if they are still avalable or not.

i agree with Booster in that you might want to limit the amount of vacuum advance into the low-40's.

FWIW, my computer controlled 93 Dakota doesnt seem to ever go over 44deg of timing.

I think all Mopar electronic distributors (except lean burn) have an adjustable vacuum advance on them from the factory. You need to slip a small allen wrench in the vacuum pod to adjust.
This doesnt' necessarily adjust how much advance you get...but it adjusts WHEN you get advance. Shouldn't take more than a 1/2 turn or so to fix your problem (I don't recall which way is earlier/later advance)