Were some distributors for those vehicles dual points?.  Were there dual points distributors with vacuum advance?  There may simply not be much room left for that in that case.

Yes and yes.

Dual points were used to increase dwell for a hotter spark.

The BOSS 302 used a DUAL POINT - VACUUM ADV for one example.

The mechanical only DIST were used for a HP Engine(s). People who bought them had no concern for easy drive-ability or fuel economy.

Unless you are operating a SATURDAY NIGHT SPECIAL on the street, the engine needs a vacuum advance, signal source of your choice properly curved (IMO).

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The HP cars equipped with centrifugal advance only were concerned with strictly one mode of operation, WOT through the RPM range. This would mean the vac advance, if so equipped, would be useless. I fully agree with all above that the vac advance is our friend on the street. In the event the throttle goes wide open, then the vac advance goes back to base and the centrifugal will then be in full control anyways. I like to first set the springs to have all in by about 2800-300 engine RPM.  I prefer using a 13* distributor cam so at say 2800 engine RPM that would mean 26* and the rest of the advance will have to come from the initial timing being set at around 10* to 12* or what ever YOUR engine likes best by trial and error as there are many factors that come in to play here. Once I have that set then, and only then will I hook up the vacuum can and begin that process.  I must admit I can cheat as I have a Allen distributor machine but a timing light and tack will work also. Fellas, I often have trouble putting in text what I'm thinking so hopefully I didn't muddy the water too much. Hope this helps, JEFF.........


64F100 57FAIRLANE500

Yes, if you can get the mechanical centrifugal advance portion "all in" at a lower RPM than it is right now, it will most definitely accelerate faster. Can also break stuff, too, if you get carried away.

There are many factors affecting, or limiting this. Both "how much" and "how soon", if you talk to somebody with a distributor machine, they will want to know everything about the car - the engine compression ratio, weight, local elevation, gearing, transmission, fuel quality, etc. "What color is it?" is usually in there somewhere, and they are only half joking. But as mentioned a tach and some experimentation can do the same thing. Just not very quickly. And Ford distributors are not particularly user friendly or convenient for disassembly down to the weights and springs. Particularly the Y Block, with it stuffed back at the firewall.

What people generally overlook is the mechanical and vacuum advance are two totally independent isolated and separate systems, they work in tandem though more or less they work at odds with each other. Clear as mud right?

The mechanical advance is strictly RPM based. The vacuum advance on the other hand is strictly based on engine load. So in typical "street" driving, stop and go, constantly accelerating and decelerating, both mechanisms are constantly adding in, and taking out, small to large chunks of ignition timing, depending on RPM and engine load. In some ways, if it was called "vacuum retard" it would maybe be better understood.

When the RPM is increasing, the vacuum advance has dropped out completely. When the RPM starts to level off, the mechanical advance is decreasing, the manifold vacuum starts to come back up. The effect is probably to cancel each other out, and maintain the amount of advance during this transition. This happens very quickly, in just a split second! If you have a vacuum gauge in the cabin you can see this in action while you accelerate, decelerate, steady cruise, climb a hill, etc. The breaker plate obviously gets a real workout! This is why when tuning, the mechanical curve is always setup first, with the vacuum advance disconnected and plugged. Like the vacuum advance isn't there. Like it's a "performance only" distributor. Takes some test drives.

Then, as someone mentioned, when satisfied, finally re-connect the vacuum advance. Make certain it moves freely, well lubed, though not worn out, etc. Further ignition advance tuning or "curving" at this point is only performed with the vacuum advance, no changes are made to the initial timing or the mechanical advance, as it has now been optomized. This is another area of common mistakes. If the vacuum advance is then found to be pulling in excessive advance at part throttle cruise, the remedy here would not be found by retarding the initial timing setting at the distributor.

Each advance mechanism is tuned separately. I've found that a good tune at highway cruise seems to run notably smoother, with a very crisp exhaust note and clean burning plugs.

So to answer your question (really!) if you wanted a range of say, 50 degrees of ignition advance for a street driven car, how do you get that with just weights?

That was the problem the engineers faced. When cruising at a steady speed in high gear on flat ground, as on the highway, very very little horsepower is needed to maintain it. Maybe 50 horsepower. The carburetor at this point is just cracked open slightly. The cylinders have a very lean air fuel mixture.

In this specific condition, 36° BTDC is not nearly enough advance for optimal fuel burning economy, among other things. I know sometimes people will say nobody cared about gas prices or fuel economy before 1972, but that isn't really true, at least if period radio and print advertising and factory literature can be believed. But, lean fuel mixtures the fire needs to be lit far earlier than a rich fuel mixture. It burns slower. Further range gains can be had by jetting for an economical cruise air fuel mixture. This requires even more ignition advance.

3 or 4 "extra" mpg on the highway doesn't sound like much with today's econoboxes but with a V8, it's significant. OHV V8 equipped cars from the 50s and 60s can achieve 20 to 25 MPG hwy with careful tuning, and still smoke the tires.

It would be possible to install very light springs, and long reluctor slots, and achieve a 50° BTDC advance at cruise, but then the engine would detonate terrible on acceleration just pulling away from a stop sign. Ping city.
See the problem?

Remember too, the typical 36° BTDC is seen only at wide open throttle, conversely when in high gear the mechanical ignition advance at a steady highway cruise may settle into somewhat less. So some vacuum canisters by design might add 15° of advance on top (or more) when cruising on flat ground, when manifold vacuum is highest, that's quite a bit of advance. This is kind of the source of general confusion, I think.

The only time (mostly) when both advance mechanisms are additive is under a specific condition of steady cruise on flat ground, when engine load is very low. In virtually all other driving conditions, the RPM constantly varies widely and so does the engine load. The idea generally though, is that at all times, under all conditions, there is very close to the maximum ignition advance possible short of any engine damaging knock or detonation.

Computerized controls and EFI obviated the need for springs and weights and jetting selection, power valve selection, and checking float height and the rest of it. It's really ingenious though what the engineers were able to accomplish 100 years ago with what they had to work with. It's all obsolete now. And so am I, most likely.

"It's all obsolete now. And so am I, most likely."  Isn't it most rewarding we can get our heads around this particular vintage engine and solve problems to get it performing better than the designers ever hoped for reliably. How interesting is life when some computer solves these problems and makes these decisions for us? I think this means I'm likely becoming obsolete too.


64F100 57FAIRLANE500

How interesting is life when some computer solves these problems and makes these decisions for us? I think this means I'm likely becoming obsolete too.

Computers can be tweaked too ...

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Wow!  Thanks for the detailed explanation.  I never knew what the vacuum advance did until now.  Makes sense.  As for my car, I have tried it both with and without the vacuum advance connected and it definitely drives better on the street with the vacuum line on.  It idles better as well. I have been working on my 57 distributor and found it to be someone finicky.  I think this is due to the roller advance plate mechanism.  I can see why they replaced it.  

If the ball bearing type breaker plate is NOT worn, it can easily be soaked in solvent, flushed and blown out with air thus removing all the hardened decades old lube. It's a precision made part, I believe by Timken. Think of all the saved money by switching over to the stamped pivoting breaker plate. One neat feature of the ball bearing assy. is the points or what ever is mounted on it rotates in a true arc about the cam, for what ever that may be worth.  It is important to insure the bonding ground wire is in good shape and secure. Also, I have discovered with success, a Ford Duraspark magnetic pickup assy. can be mounted to the bearing plate with modifications. If anyone is interested in doing this, I'll be glad to post pics. That being said, if the bearing plate is worn, they are pricey when ever one is found. Hope this helps, JEFF....................


64F100 57FAIRLANE500

It is important to insure the bonding ground wire is in good shape and secure.

Correct as if the DIST is not grounded correctly the current will pass through the plate and cause the ball bearings to go out-of-round.

This plate style was better but also costly to FORD.

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I have a NOS Plate if You need it Phil. Bought it on Ebay for $75.00 and then bought a NORS One which has a lot more Balls in it so I will use it instead. The Balls in the Originals tend to go flat also because they only move a little each  timele each time the Plate Advances as well as because as noted lack of a Ground Strap causes the Balls to deteriorate.

  

NORS One which has a lot more Balls

NORS ... ?

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