Educate me on the electronic assisted vac advance dist.

Car in question is my 73 RR 400 4 speed. It has this type of advance distributor which I have never messed with one like this before. What is the good the bad and everything in-between with this type. Here is a picture and description. This is a NOS vacuum advance unit for the distributor for the years and makes listed below. This is for the electric assisted distributors. This is a original NOS Mopar part in it’s original packaging

Heh. It was used with certain cleaner air systems (CAS) in the early 70s.

This MTSC says your 400 was the engine that would get it in '73.
http://www.imperialclub.org/Repair/Lit/Master/302/page06.htm

Now that one says the purpose is easier starting.
I don't know if that's a completely accurate explanation. Dodge FSM shows 10* BTC and I don't find any TSBs that change that.
10* BTC should not be a problem starting.

1971 MTSC shows a similar (or same?) vacuum adavance for 383 and 440s.
It disconnects the vacuum advance on deceleration.
http://www.imperialclub.org/Repair/Lit/Master/287/Page11.htm

That explanation makes sense. When the throttles are closed, manifold vacuum (under the throttles) pulls the fuel. Restrictions in the passages are set to provide an air-fuel mixture at idle speed. But on deceleration, the throttles are closed at rpms above idle. The manifold vacuum will be higher than at idle and mixture richer. Richer mixtures take less time to burn so vacuum advance is not needed on decel.

This is often a non-issue because the vac advance was often connected to a manifold vacuum port at or just above the throttle blades. So vacuum advance wasn't added at idle,
My guess is the 383 and 440 (and 400?) engines either use manifold vacuum, or have the blades right at the vacuum port. The latter is most likely. Emissions packages generally ran leaner idle mixtures than their earlier non-smogged conterparts. Also cams sometimes had slightly more exhaust dilution at idle. These factors required higher idle speeds to runs smoothly (compared to their earlier counterparts).

From the FSM:

Mopar had 2 different ones in the 70 to 78 era. One retards the timing at idle when the wire is grounded by the idle speed screw and some were on the idle solenoid.
The other one would advance the timing about 10 degrees while cranking the eng. I believe it was actuated by the starter relay. Ron

Thanks for the replies and info, so if one wanted to recurve the distributor would it make sense to pitch this type of distributor for a vacuum only unit?

If the leads aren't connected it behaves just like a regular vacuum advance.

Well don't pitch it. Someone will want it. Not a lot of people but very much needed for a correct restoration.

As far as recurving, it depends on exactly what you've done to the engine, and how you're going about recurving, but unlikely the solenoid equiped advance will be needed.

If I pitch it I'm only going to remove it and keep it on the shelf, the car is a survivorish ( is that even a word) 46k mile car I purchased from the original owner so anything original is not going anywhere. Engine is completely stock I'm just looking to wake the car up some. I'm thinking the vacuum advance may not be working, again it's an assumption as I have not really looked into the timing yet.

Those early emissions years, especially around '73, they were really doing a balancing act with compression, timing and fuel.

The Dodge FSM actually has two 400 cid specs. I missed the second one before. The other has timing start aroun 7.5 BTC. Not terrible but you can experiment with 10*. That's within the tweaking expected.

IMO the one emission trick that really hurt throttle response are the timing delay systems. One was called OSAC - Orifice Spark Advance Control.
Not every engine had them. But if yours does, learn how it works and then take it of action so there's no delay.

A pretty complete list of Master Tech is here
http://www.imperialclub.org/Repair/Lit/Master/index.htm

TSBs here
http://www.hamtramck-historical.com/library.shtml