Dual Point Dizzy

[Mark D]

Haven't been that active here in the past couple months, hope you all have had a healthy winter so far. Been doing some learning in the past couple months on the advantages of dual points.  Those of you that have seen my posts in the past know that I'm not afraid to tackle a project, and for me personally its the best way to learn about the subject in front of me.  So rather than tear down the dizzy I am running at the moment I've decided to collect the parts that I think are needed and build one. 

 

It started when I came across this dual point breaker plate on ebay. Listed as: 1950-54 6 cylinder dual point distributor plate 406-D. It was cheap enough at $20. 

 

 

Next I found a whole carton of dual points for $12. (shout if you need some - there's more than enough to share).

 

Lastly I found a NOS dizzy listed as Chrysler 6 cylinder ARMY issue.  Paid almost nothing for this compared to the rebuilt stuff I am seeing listed.  Curiously enough it does not have a vacuum advance. I am sure someone can expound on the lack of that feature for me and why army issue engines would not need it. Could also be possible this was meant for industrial application.  It's enroute to the house at the moment. When it arrives I am curious to see if I can't add the vacuum advance.  Any insights on this appreciated.

 

I am missing a dual point condenser.  In the process of my investigating what I should be looking for, I've learned that the condensor must be matched to the system and that the contact opening time, dwell etc must also be taken in to account.  From what I understand the mfd rating must be sized to match and I am looking for input as to what the appropriate mfd rating would be a 6v dual point setup.

 

I did find a nice little laymans description of the purpose of the condenser on the HAMB that I will include here for future posterity and future searchers. "The purpose of the condensor is to prevent arching at the contacts, when they first start to open ( firing the coil) the current wants to continue on across the gap. The condensor then provides another (easier) path for the current to go. By the time the condensor has filled to capacity (mfds) the contacts have opened to a gap that the condensor (current) can no longer jump. Then when the point gap closes the condensor will discharge to ground through the contacts. Too small of a mfd rating and the condensor will fill and discharge as they open , too large and the condensor will discharge incorrectly as well. Both cause a unstable firing event."

 

Fortunate to have member "Moose__" in the area and he's got distributor tester from way back in the day to test this frankenstien once the part are all in place. And he's offered me a core dizzy if this army issue doesn't pan out.  Eventually in the future I'd like to build a pertronix version for comparison as well.

 

Thanks in "advance"

Edited February 13, 2014 by Mark D

[Frank Elder]

Don runs a dual point Mallory in his monster...maybe he has the skinny on condenser supplies. The Army probably wasn't worried about mpg as  much as horse power on tap.....

[Don Coatney]

I have been running dual points for years. I have the same setup as you. I do not recall the condenser part number I use. The Crashler military distributor you have coming may be for a long block 25" engine. Check the shaft length as the long block distributor has a longer shaft than the short block distributor. One of the prime functions of a vacuum advance is increased fuel mileage. I don't think the military was concerned with fuel mileage. Also engines used intended for operation at a governed speed or racing engines had no need for a vacuum advance. Pictured below is my bench top distributor machine.

 

Most all 12 volt contact point ignition systems actually run on 6 volts.

 

 

 

 

 

 

 

 

 

 

[greg g]

Mark the basic purpose of the Dual points is to increase dwell and allow the coil to acquire more juice before discharge therefore giving a hotter longer spark. If you notice the breaker plate positions the points at slightly offset position in regard to their cam high spot. So while one set is closing the other is positioned to stay open a couple degrees longer. Most likely you mil spec dizzy came off either a stationary engine application, where rpms are governored to remain in a relatively narrow band in operation, or a water proof situation where entries into the dist body are limited. Did you get the proper cap? Is it for a short block or long block application? (the drive pin on a long block engine will be longer and need to be changed to work in a short block) Give Don C a shout as he has a dual point set up in his car.

Now to hotter longer spark, I don't see the big advantage. once any spark ignites the air fuel mix, the effectiveness of the charge is based on how tight it was squeezed, and how fast the flame front of the combustion travels. For the most part a longer spark is firing into an inert substance. Granted there will always be some unburned fuel left in the cylinder, but that is more a result of quality of fuel, proper fuel air ratio, compression, and atmospheric conditions, than brightness or length of spark. Conventional wisdom would suggest that hotter longer spark might be necessary in very high CR engines but for most street applications all that is needed is enough spark at the right time to light the flame. That said, knock yourself out and enjoy your project.

[Don Coatney]

Don runs a dual point Mallory in his monster...maybe he has the skinny on condenser supplies. The Army probably wasn't worried about mpg as  much as horse power on tap.....

At one time I installed this magical electronic point driven box. First drive around the block the engine died when I stopped at a stop sign. Re-fired the engine, drove home, and removed the magical box and coil.

 

[Mark D]

Greg - Adding the thought of CR to the ratio makes sense. Obviously I got more learning to do. I doubt that I will notice anything by the change, but as I said, one project at a time builds proficiency for me. To answer your question about he cap, yes, it came with a cap and supposedly has never left the box the it was packed into at the factory. Will be fun to see what this thing turns out to be when it arrives.

[martybose]

At one time I installed this magical electronic point driven box. First drive around the block the engine died when I stopped at a stop sign. Re-fired the engine, drove home, and removed the magical box and coil.

 

It all depends on the application.  I've worked on several race engines that were absolute bears to get started and ran poorly when cold.  In all cases adding an MSD system made all of them start up just by pushing the starter button, and they idled smoothly even when stone cold.

As always, YMMV.

 

Marty

[William Davey]

In addition to the clarification provided by Greg G above, the main advantage of dual points is in higher RPM applications where the power of the spark is limited by the time the coil had to recharge after each plug fires.  My 1955 C-3-B8 (259 cu in V-8) had dual points, but with a red line of 4,400RPM, I doubt if there was much benefit on this or any engine turning that slow.  The 1970 Duster 340 I had back in the day definitely took advantage of the dual point capabilities with a red line of 6,250.  Not really a red line, but the valves would begin to float causing a slight bobble that limited RPM and top speed to about 136MPH!.  Wish I still had that car. 

[Don Coatney]

The main function of dual points is to increase dwell angle or the time the points are closed (not open) allowing coil saturation. When the points open the coil very quickly discharges and fires the spark plug. The overlap with a dual point setup allows the points to stay in the closed position a few more degrees of rotation. The link below explains it very well.

 

http://randysrepairshop.net/basic-ignition-system-theory-of-operation-how-it-works.html

[Mark D]

Been a while since I updated this thread, been busy with a few other projects. The military dizzy arrived shortly after I bought it.  After comparison it is too differnt for me to try to mod, so it'll go back on epay for some lucky dodge staff car owner. Anyone interested in owning it should get in touch with me via PM.  So fast foward a few weeks, I got another used dizzy off epay (cheap$) and cleaned it up for the transplant.  Last night I was fooling around with it, and started to install the dual point plate. Didnt notice that at the time that the tab which connects the vacuum advance to the plate is not in the same place.

 

Question before I begin searching later model year specs, does anyone have the model number for the vacuum advance which corresponds to the dual point plate? 

 

Hey Don did you run into this?

 

thanks all - Mark

 

 

[Young Ed]

Mark there are 3 that I know of styles of dist housings for cars. Each takes a different cap rotor and some a diff vacuum advance. There is a pre 48 (and maybe more really early ones) a 49-50 and a 51 and up to?? Do you know what those dual point plates are supposed to fit?

[Mark D]

I googled the mopar points part no, and I got this response. Guess I'll try a search from these.

 

NORS DISTRIBUTOR POINTS SET FOR;(6CYL.)

CHRYSLER,DESOTO 1950-54

DODGE,PLYMOUTH 1950-58

[moose]

Hey Mark, this is a IAT-4101 that came with a P24 motor I bought recently.  Looks like just what you need.  Come and get it.

[Don Coatney]

I did not have that problem.

 

[Mark D]

Thanks Moose!! - I'll be down in a couple weeks. Will coordinate for after Easter. Got a plate full of things going on at the moment.

Hey Mark, this is a IAT-4101 that came with a P24 motor I bought recently.  Looks like just what you need.  Come and get it.

[fordkustom]

Standard #: VC 3

Filko #: VC 12X

AMC #: 3209168

Presto #: 1AT2023LS

1AT2023RG