Where the conventional distributor gets a “dyno” test:
For the majority of the 20th century the automobile ignition distributor has been responsible for the accuracy of spark timing and helping ensure the intensity of the spark. The arrival of microcomputer-controlled ignition in cars starting in the mid-1970s with Chrysler’s pointless-ignition (that’s a distributor without “contact points,” not a distributor with no purpose!), by the 1980s most automobiles had moved to so-called “electronic ignition.”
Where the earlier mechanical “contact points” acted as a switch for the low-voltage side of the ignition system, ultimately the task of “switching” the flow of electricity “on” and “off” has been given to transistors – which are at the heart of computers. Since transistors have no moving parts (except the electrons traveling through them at 186,000 miles per second), hence the term “solid state” moved from describing the platforms of radios and TVs to cars.
Yet much of the reward from tuning conventional (earlier non-computer/mechanical-switch contact point) ignition systems comes from being able to access and easily modify the “tuning” characteristics of a particular distributor/vehicle. Using the Sun brand distributor machine shown in this picture, after removing the distributor from an automobile during a tune up, the distributor can be “bench tested” for specific performance characteristics. Most notable on the 360-degree dial surrounding the spinning distributor was the ability of the machine to indicate exactly how much spark advance the distributor provided at all engine speeds. As the engine speed increases, the “timing” of the spark must occur sooner to ensure that combustion is complete and “optimum.”
While the need for a distributor bench-testing machine, such as the one shown here at the start of my automotive career, has been phased out due to predominantly computer-controlled ignitions, the capability for ensuring accurate/optimum spark advance is still a goal of auto technicians. Today we service vehicles with computers that modulate the exact timing of the spark for maximum performance without pinging (detonation). In the earlier dyno-tuning shop that I started in, we “tuned” the distributors for the best profile for performance – which was enjoyable, if not as precise as today’s “smart” (computerized) cars.