This post revised 3/2/2012...
Based on my research(which is sketchy at best) the following donor motors have Duraspark I(California only) or II distributors hereafter referred to as Duraspark that will fit into a 351C:
Years 1974-79
Motors 351M, 400, 460
Vehicle Type Car or Truck. Not a factor
There may be later years that will work, but I have not yet found a reliable source. My understanding is the key to the distributor choice is to select an engine that is carbureted. Carbureted engines(old school engines) relied on parameters such as manifold vacuum or centrifugal force for timing adjustment. EFI engines rely on a variety of sensors. As a result, the timing adjustment parameters I need are not built into EFI distributors.
For those who need to know why I want this distributor....
The reason for utilizing the Duraspark distributor is to take advantage of the Ford Motorcraft electronic magnetic triggers(i.e. Hall Effect) Trigger. This trigger was the first electronic replacement for Ford's mechanical points and is known to be the gold standard for ALL triggers because it is:
1. Easily diagnosed
2. Easily bought over the counter at your local parts store
3. Cheap
4. Reliable(decades most likely)
5. Quick to replace
6. Great trigger signal
7. Compatible with most if not all ignition boxes...including HEI* modules.
This trigger is not the equivalent of mechanical points. Mechanical points were wired directly to the coil whereas the magnetic trigger module requires wiring to an ignition module which is wired to the coil.
Ignition modules are "smart" devices that allow the ignition coil to be charged more effectively than points. Points were limited for several reasons:
1. Voltage utilized by points was limited to prevent arcing.
2. Low voltage of points meant low voltage to coil.
3. Points wear over time..there was that little plastic guide you had to lubricate.
4. Once set, the dwell was fixed over the engines RPM range.
Most importantly, the ignition module stopped the ever popular: "Honey, I left the keys in the ignition and now the car won't start" issue. This occurred when the wife left the ignition on at a time when the points just happened to be closed, causing the coil to be charged and charged and charged until it got hot and melted the insulation of all of it's interior windings.
Contrary to popular belief, this distributor when coupled with a "high voltage" coil does not require use of a large diameter cap. The requirement for the large diameter of the cap was never based on electrical crossfire, but on the following:
1. Extra space was needed to mount the coil into the top of the cap as in early GM designs. This is really a stupid place for a coil, IMHO.
2. Allows easier routing of ignition wires between terminals than the smaller cap. This is why I use it.
3. Marketing...EVERYONE who sees a large cap thinks High Voltage Electronic Ignition regardless of actual performance.
4. I think every aftermarket "high" voltage vendor now sells their distributors with small caps to SAVE space without detrimental results.
Granted, the stock vintage Duraspark distributor is not a shiny billet, but it's not ugly. If you want to have a "stock" looking distributor with a true high voltage ignition system, this distributor is the way to go. The cap and rotor for this distributor are available everywhere and cheap(not sure this always the case for aftermarket distributors) . And if you rebuild it right, or buy a quality new or rebuilt version of this, it should last 200k miles without changing electronics.
Photo 1: Looking Down Into 351W Duraspark With Cap & Rotor Removed
The blue component is the magnetic trigger. There is no ignition module in this distributor(see Photo 3). It could be mounted opposite the trigger in a large cap distributor.
Photo 2: 351W With Large Cap Duraspark Distributor
Here you can evaluate the size of the large cap for fitment.
Photo 3: Sample HEI Module
This is just one of many ignition modules you can use with the Duraspark I magnetic trigger distributor. This style known as the GM HEI module, is small, cheap and available everywhere(keep a spare in the glove box...Pertronix guys know that). If you get the right one, it will deliver the proper amps and volts to energize your coil to its full potential.
The Ford equivalent of the small black HEI ignition module shown in Photo 3 is the Duraspark I or II ignition module. You would recognize this as the square, finned, aluminum brick typically mounted on a fender well of 1977+ Fords. I find them to be big, ugly, expensive and hard to find. It would be tough to fit one of those in a distributor. I also went through 4 of them in 10 years time. But, others swear by them.
I intend on testing/measuring spark voltage, spark duration, spark gapping, and the effect of heat with at least a few different coils and a few different HEI modules. I am curious what the difference in performance is, because there are big differences in price.
I also hope to actually cut into some of these coils to have a look. I have been told from a trusted source that round coils should be mounted vertically. As far as I recall, every stock Mustang I ever saw had the coil horizontal on the manifold. I never had any problems...200k+ miles. But then again, I never strayed from the stock ignition setup.
Note regarding Pertronix modules, of which I have 2 vehicles running with them. Pertronix modules that fit under your stock ignition cap SIMPLY REPLACE THE POINTS. These modules are not HIGH ENERGY. The current and voltage that flows through them is not adequate to provide a huge kick from the coil. They do help with dwell, no doubt about it. But this is tiny in comparison to using an HEI Module to up the voltage/amp input to the coil.
Here is a great resource for additional information:
http://www.mre-books.com/sa69/sa69_8.html
*HEI means whatever the seller wants it to mean. A High Energy Ignition
SHOULD MEAN ignitions which
PROVIDE at least DOUBLE the ENERGY of the standard/mechanical point equipped ignition systems of pre-1970 engines as measured
AT THE SPARK PLUG. But, with a single exception, I don't recall ever seeing any objective data in regards to measuring the voltage/spark duration at the plug that would justify calling an ignition system high energy.
Replaced Photos 1 & 2
Photos 1 & 2 courtesy of anonymous
Photos 3 & 4 generic photos
Revised 3/2/2012
Added Duraspark I(CA) and II.
Added great signal to advantages,
Deleted next generation Duraspark II.
Corrected information regarding hall effects.
