The Mopar electronic ignition system introduced in 1972 was cutting edge in its day. While everyone else was using the ancient points-type ignitions, Chrysler scooped 'em all with the electronic unit.

A magnetic pickup coil in the distributor is triggered by one of eight tips of the rotating reluctor, sending the signal to the ignition control box to fire the coil via internal transistorized electronics. It was a giant leap forward over points, which were nothing but mechanical switches handling the primary voltage of the ignition system. That was a long time ago, and the Mopar electronic ignition concept has changed little since then. As a basic ignition-triggering system, however, it just doesn't get any better. Reliability, accuracy, and high spark energy were all hallmarks of the original system, and over the years, the system has been refined with better and more modern electronics.

Do you get the feeling that we kind of like Chrysler's electronic ignition?

The Mopar electronic system is comprised of three key components, each of which contributes to the performance of the system. First, of course, is the distributor. The distributor's function is simply to act as a switch, sending a signal to the control unit to fire the coil, and routing the spark energy to the plug wires.

Now that we've already gone through the three major players-the distributor, control unit, and coil-let's have a closer look at the distributor.

As a switch, the distributor's first function is to tell the control unit when it's time to fire. This is timing, and the event occurs when one of the eight tips of the rotating reluctor comes in line with the magnetic pickup unit. Complicating things is the fact that timing has to vary under various running conditions, so the distributor has provisions for altering the timing. This function is handled by the advance mechanisms enclosed in the distributor.

Two systems are employed to alter the timing: the mechanical advance and the vacuum advance. Since the signal to fire is given whenever the reluctor and pickup line up, varying the timing has to be accomplished by changing the relative positions of these two components. The mechanical advance mechanism uses centrifugal weights controlled by springs to rotate the reluctor forward relative to the pickup. The vacuum-advance mechanism uses a vacuum diaphragm to pull the pickup unit, mounted to a pivoting plate, back relative to the reluctor. In a high-performance application, the mechanical advance is the most relevant, since at wide-open throttle, there's no vacuum, so you won't see any vacuum advance. Performance-tuning a distributor mainly involves getting the mechanical advance optimized. There are two characteristics to a conventional mechanical advance system, which boils down to "how much?" and "when?"