The Stovebolt Site Forums The Shop Area Engine Shop What for, those dual points?

Good point, Waldo. Yes, there is an optimum saturation point where the magnetic field won't get any stronger. In the General Motors HEI ignition system, for instance, there is a built in "current limiter" which attenuates the primary current when the theoretical saturation point is reached. It can be observed on the primary waveform of an oscilloscope as a drop in the raster pattern line voltage about 2/3 of the way to the transistor cutoff point to trigger the next spark in the sequence. I can tell if an original-equipment GM ignition module is in use, or one of the cheaper aftermarket models, simply by looking at the primary scope pattern.

Now, jump back about 40 years. None of the solid-state wizardry of the 70's and 80's and later times was available to the guys building high-performance ignition systems just after WW II. They had to make do with what they had, and dual points were one of the ways available to improve ignition performance. Since primary current flow is opposed by both the DC resistance of the coil, and the inductive reactance of the coil winding, plus the action of the points' contact resistance, adding a second set of points to share the current load was a logical improvement.

At 4,000 RPM, the points on a stovebolt six are creating 12,000 sparks per minute. That's 200 sparks per second, and each one has to happen at precisely the right time. Given the somewhat primitive operation of a set of mechanical points, a centrifugal advance system, and a vacuum advance, I think the engineers of the day did a pretty remarkable job with the options they had at their disposal!
Jerry