I believe the "trick" is to get the mechanical advance to work right - plenty of early advance, 36° limit, and all in by say 2800/3000 rpm. This is done with no vacuum advance at all - the distributor hose is pulled and plugged (got golf tees?).

When your mechanical advance is capable - then you add sufficient vacuum advance to enhance the economy. In my case I've got it limited to about 7° maximum and thats all. The extended early advance prevents using too much more without spark knock. My outfit has a stocker cam - the heated up version you are running will take a different set-up I'm sure.....

 
 Steve Metzger       Tucson, Arizona

Because vacuum advance, along with tach drive, is part of what I want. I already had a distributor without it. I know the world will not end.

joey

Why not just FORGET ABOUT the vacuum advance for now. For years lots of cars came without any vacuum advance and the world did not end.

Harbor Freight, and most other places sell a dial-back timing lite that one person can operate.

Get the mechanical advance set right and then go from there. Don`t try to multi-task on this one. Pete

PS any NAPA or any parts store will have a distributor cap for a 57-74 ford V8. Try one

Update:

The advance on this distributor at present stops advancing at 2900 or 3000 rpm, with a total of about 36 degrees. That is with the vacuum connected. I have to do more interval checks comparing numbers with the advance line connected/disconnected. But it appears at first look that the vacuum signal from the Demon isn't very strong at all.

However I was again having trouble with the darned distributor cap. Just the normal vibration of the engine jiggles the cap enough to make the engine run rough. Grab the cap and hold it in a certain position, and everything smooths out. Because of this a road test isn't doable, so I have no idea if this distributor will be an improvement over the previous.

Yes, that's all correct.

Yes, I have restricted mine a bit as well. Actually using one for a 3.3L engine.

You are powering a vacuum pump with the small direct port, correct? and the ported vacuum would then go to the distributor vacuum pot.

If you are using the ported vacuum source for the distributor, an initial value up near 14° would be appropriate for cammed up engine - but you would have to limit the slot travel so that you only got 22° (11° at the dizzy) to avoid going over 36° total mechanical.

My Road Demon Jr. pulled so much air through the PCV that I had to restrict it - otherwise the idle ran up too high. There are smaller passage PCV's available to do the same job. 

 
 Steve Metzger       Tucson, Arizona

OK, I've solved one issue. Demons have 3 vacuum sources at the baseplate. One large, at the back, is direct, and I use that for PCV.

Then there are two ports, side by side, along the baseplate on the passenger side. I ASSumed that since they're less than an inch apart and both brass fittings resemble each other that they were both ported, that is, above the butterflies. But they're coming from different sources. One is direct, while the other is ported.

When I didn't require vacuum to the distributor, I had one capped off, and the other hooked to the vacuum pump. So now, can I hook the vacuum pump up to the direct port? My Ford shop manual doesn't specify.

This diagram shows the way I stop the travel at 13° - its then 26° at the crank. With 10° initial this makes a total of 36° - a good total value for a Y-block. The full slot shown on a standard upper rotor is good for about 20° - therefore 40° at the crank, which is way too much if you experiment with elevated initial values or really light springs. Could be previous owner used light springs and a very small (or TDC) initial. 

 
 Steve Metzger       Tucson, Arizona

Joey - If you are using the ported vacuum port, it should have no vacuum at idle with the throttle blade very near closed. So attaching the line - or detaching it - at idle shouldn't have an effect on the engine speed.

The Autolite distributor would have the "slotted" type of centrifugal travel stops in the upper rotor shaft (has the cam above the point plate). Upper LH in this picture. 

We usually shorten the slot to limit the total advance added by the centrifugal mechanism - and as Charlie says, control the speed it comes in by changing the springs.

 
 Steve Metzger       Tucson, Arizona

The springs will change the rate of advance. To change the amount of advance, I believe, will require that you either grind the slots to get more advance or braze or weld the slots to get less advance on that particular distributor. I'm more familiar with the Motorcraft distributors.


Lawrenceville, GA