Timing Dance ! Vacume Advance ?

T67POWER said
I don't take the chance of being in the wrong situation and having the motor pay the price.
FOR EXAMPLE: HOT DAY\\BIG HILL \\ THREE QUARTERS THROTTLE.
REMEMBER (((( YOU CAN'T ALWAYS HERE DETINATION))))

If it's all about drag racing then it gives you no benifit, and you will not have any detination problems creep up on you.

T67,
The vacuum advance only operates at light load situations where the manifold vacuum is high. In your example; up hill with the throttle 3/4 open the manifold vacuum will be low and there won't be any (or very little) vacuum avance and at WOT acceleration there won't be any vacuum advance at all. The vacuum advance does not react to rpm changes it reacts to changes in manifold vacuum. When the throttle is just cracked open you have maximum manifold vacuum and maximum vacuum advance. When the throttle is fully open you have minimum manifold vacuum and no vacuum advance.

With any modified motor the initial timing, total mechanical advance, rate and vacuum advance have to be dialed in for the combo. The total amount of advance the vacuum pod can add is fixed by the stop built into the arm of the pod. There is a number stamped on the arm which represents the number of degrees the pod can add in cam degrees (double this number when talking about crank degrees). But the vacuum required to get it to start moving and the amount of vacuum to reach full advance is adjustable with an allen wrench through the vacuum nipple. If you had a situation where you had detonation under a light load situation or under light acceleration then you would adjust the pod so the advance starts coming in at a higher vacuum level. If you had the same situation with the vacuum advance disconnected then the timing is coming in to fast and you need stiffer springs in the distributor.

pilotsf,
I don't think you have said what distributor you have but with 17/18 initial and 34/36 mechanical it sounds like you have the mopar perfromance distributor. These come through with very light springs (likely the pink ones) which may have your timing coming in too fast. You may need to go to stiffer springs. These distributors have a Mallory advance mechanism in them and there is a tuning kit #29014 that you can get from Summit or Jegs that has a wide assortment of springs and a chart that shows you which springs or combinations give which timing curves. Remember as you reduce the amount of mechanical advance built into the distributor with the stops you have to go to stiffer springs to have it still be all in at the same rpm.

On my 360 I needed 17 initial and with the magnum heads I have, I run 33 total mechanical. With the light pink springs it would be all in around 1800 rpm. To get it back up the 2600 rpm range I need to go to the next to stiffest brown springs.