Vacuum pod

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valiant1966

valiant1966

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Can someone tell me what the different numbers on the arms of the distributor vacuum pod mean? I have seen it on here somewhere but can't seem to find it now. I have a distro in my car that has an 11.0R stamped in it and another distro on the bench with 8.5R on it. Is one more desirable than the other?
Also, there is an adjustment with a 3/32 allen wrench in the vacuum pod. I know this moves the advance but does it move the initial or total or what? Why move it with this adjusting screw rather than just loosening the distro and moving it? Thanks for any help. Dennis
 
That is the amount of advance in degrees but it's in DISTRIBUTOR degrees which is 1/2 crank degrees. Many mechanical advance mechanisms have the same marking, often on the bottom of the "top hat"
 
Dart273 is correct.

The allen wrench adjustment changes the rate of advance, the stamped number tells you the amount of max advance.

 
I ordered the vacuum advance for a small block distributor from RockAuto that was described as "for improved fuel economy". The one I received had 8.5R on the arm, and nothing describing the economy. I would think 11.0R would give even better economy since no vac advance yields the poorest. Sorry, not much help but maybe a small data point.
 
Tuning a motor and distruter is a lost art and depends on your motor combo....there is no cure all.
Somewhere I have an old article on how to tune a motor properly..you need a vaacum gauge, timing light and a tach.

I will try to find it.
 
BillG...that's good stuff to know since I'm looking for performance , not economy.

jos51700...thanks. Being able to control the rate of advance could be helpful. I like that.

mbaird...know what ya mean. But since no cars have a distro any more and you can't control most things, the computer does, no wonder no one understands these things any more. As for me, I still have my dwell, tach, vacuum gauge and other tuning tools from back when I started in the 60's(yeah, I'm that old) and they still work good.

This is a good start. Another question. Wonder how many turns I can get out of this screw in the dashpot or if I can mess it up by testing the limits(other than brute force)?

Wish I had one I didn't mind messing up up to try it on.
 
Vacuum makes it go one way, a return spring makes it go the other. The screw changes spring resistance. I don't know if you can over adjust that and/or screw something up in there or not. If the vacuum supplied to the pod is about where factory determined, I wouldn't mess with the screw.
If you up the base timing to around 16 BTDC to get a better run from todays pump gas.
you've added 6 or more degrees to where the vacuum advance is going to take the timing to and to the total/all in advance.
Shortest and earliest vacuum advance response could be the best route or setup , I'm really not sure.
34 BTDC total/all in at 2500 rpm is where doctoring the centrifugal advance comes into play when the base timing is raised.
Like stated before , there isn't a single cure all at that vacuum pod.
 
jos51700 said:
Dart273 is correct.

The allen wrench adjustment changes the rate of advance, the stamped number tells you the amount of max advance.
Click to expand...

Don't be surprised if your original distributor isn't adjustable. Mine wasn't but I think most newer distributors and replacement diaphragm's are. tmm
 
Just buy the issue of Mopar Action from a few months ago that talks all about specifically this. In fact, it's been covered in MA (and the benefits of tuning your advance curve) several times over the years. I found out that my reman distributor had a fixed rate adjustment in it, and I was pissed! I'll be rebuilding my own from now on.

Feb. 2013 issue has what you need:
http://www.moparaction.com/Next/history/feb2013.html
 
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