The one shown is a 59A Ford converted from dual point/single coil to dual coil. A tab was added to the rotor and a copper ring matching it screwed to the cap to convert the secondary system. I don't know what points were used in this particular conversion, but they would have had to have been reoriented on the plate and the cam cut down to 4 lobes.
Thanks Bruce. Pardon my ignorance but what was the goal? A fatter spark? Dual plugs? Alternate firing?
This is a Harmon Collins dual coil for a a flathead. This is a later Spalding Famethrower for a SBC. I believe it is the same Mr. Spalding that was later bought out by Grant. All of them are actually dual 4cyl. ignition systems contained in one dizzy body. Each had it's own coil, condenser, balast resistor and set of points. As I understand it, the 4 lobe cam allowed more dwell to charge the coil longer and give a stronger spark. Some said that the higher winding Chevy motor had less point bounce at the higher RPMs. The right side of the HC rotor above is just like a standard rotor. (center contact) The left side has a contact hidden underneath that rides on the br*** ring of the middle section. With the alternating fireing, the fireing order of the cap had to be changed. The flamethrower fires each bank as a separate ign. system.
Woa! Nice ingredient to add in a vintage souped-up motor rebuild, me thinks. Thanks for the pix & 'xplenations Tommy!
A stock distributor will not function properly with the higher Rpm's of a pumped up motor. This is primarily due to the fact that a coil needs a certain amount of time for the magnetic field to build up in it's iron core. Each time the distributor fires a spark, the coil is completely spent as far as it's magnetic field is concerned and this field must be built up again before another spark can occur. The time which is allowed the coil to build up the magnetic field and be able to generate another spark is controlled by the distributor. A single point allows 45 degrees for this process to occur, while converting to dual coil, dual point set-up allows twice this amount of time, or 90 degrees for coil saturation. This extra time allows for your motor to wind up faster without skipping a beat. Tom Spalding's conversion was one of many, Potvin, Harmon & Collins, Kong, Kurren, Roemer to name a few.
The standard ignition (the 21A/59A basis of both conversions above) had two point sets operating roughly 10 degrees out of phase, with the extra set allowing the single coil extra dwell time. This is a Mallory design used on flatheads from '32-48, chosen because the 8 cylinders and high operating speed (for the time) of the flathead were a stretch for the coils of the day. The dual coil conversions have 4 lobes removed from the cam and the points moved so that alternate firing cylinders fire from alternate coils, increasing dwell even further. The Spalding was a very simple conversion with no extra parts needing manufacturing with anything more elaborate than a drill press, while the HC was very elaborate with special cap and rotor parts that are now a major problem because replacements are nearly unfindable. The earlier popular racing distributor was the 12 cylinder dual coil Lincoln distributor converted with a four lobe cam and rephased points to act as a very compact and neat dual coil for the V8. I have a number of these with a number of very different conversion techniques employed to overcome the rotor and point phasing probs. All this stuff is neat ancient high tech, but not needed for street flatheads and pretty much obsolete for racing ones. I have HC and LZ types, but would be hesitant to use them much because of the rare basic tuneup parts--either would have to be backed up by a spare stock distrib on the road in case anything failed. I don't have a Spalding (or any of the other similar simple conversions) but I have or have seen rotor and cap conversions, which are dirt simple and could be made by anyone in an easy afternoon. I would handle the points conversion by redrilling the plate for reasonably compact modern (modern points??!?) point sets and the result would be a piece with readily available parts.
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