In 1965, hot rodders were baffled by this ignition system with just one spark-plug wire to fire all eight plugs. How could that ever work? It did, and here’s how.

Readers of Hot Rod magazine in June, 1965 were stunned and baffled by a photo (above) that appeared in a colorful two-page gravure feature on the Oakland Roadster Show. Pictured was a ’23 Ford T-bucket roadster powered by a Buick nailhead V8 with a mysterious ignition system. There was no distributor, only a single coil-like component at the front of the engine with one plug wire feeding all eight spark plugs in series. That couldn’t possibly work . . . could it?

A caption below the photo insisted that yes, the engine did indeed run—in fact, it won the show’s engineering award—and the magazine followed up nearly one year later (April 1966) with an article explaining the Kaehni ignition, as it was called. Intriguingly, the story was titled “It Won’t Work!” and then proceeded to explain how it did. Still, the doubts and confusion persisted, so we thought it might be fun to explore the story further.

Charles Miller, the owner/builder of the Buick-powered Model T roadster at the show, was a research and development engineer for the Economy Engine Company, which specialized in the stationary gas engine business, mainly for the petroleum industry. His ignition setup was an adaptation of a system developed for the company by Frank J. Kaehni, who was awarded U.S. patent 2,968,296 for his creation. The drawings and text in the patent filing provide plenty of information.

Yes, the Kaehni ignition did indeed fire all the engine’s spark plugs at the same time. In fact, it fired them continuously, as long as the ignition was switched on and the engine was running. A solid-state, transitorized oscillator circuit operating at 1.2 kHz supplied a trigger signal to an inductive coil that stepped up the vehicle’s 12-volt battery supply to around 45,000 volts at the plug gaps. How it works: While all engine’s spark plugs are firing continuously, only the cylinder on the compression stroke has sufficient fuel, air, and pressure to initiate proper combustion.

In that regard the Kaehni system is somewhat like a glow-plug model aircraft engine, or the waste-spark ignition system used on many familiar engines—Harley-Davidson four-stroke V-twins, for example. On a Harley, both spark plugs fire at the same time, but one cylinder is on its compression stroke while the other is on exhaust, so the engine runs normally (for a Harley, anyway). The Buick 3800 V6 (others, too) employs a similar setup, with the no. 1/4, 2/6, and 3/5 cylinders each sharing a common coil and firing their spark plugs at the same time.

Kaehni Ignition prechamber configurations

Along with the solid-state circuitry, a novel feature of the Kaehni system was a modified cylinder head with a small, narrow chamber that housed the spark plug, variously described as a prechamber or ante-chamber. As the piston approached top dead center on the compression stroke, a pressurized charge of fuel and air was forced into the prechamber for combustion, promoting a more positive ignition event. The size and position of the chamber in the cylinder head could be tuned to alter the ignition timing to some degree.

So yes, the Kaehni ignition system worked, absolutely. However, how well it worked is demonstrated by the fact that nothing like it has ever been adopted by the automakers for use in production cars. There, internal combustion engine development is currently  focused on timing and metering fuel, air, and spark with total precision. By the way, the Economy Engine Company is still in business as Altronic, LLC, a unit of Hoerbiger Holding, and it still supplies ignition systems, controls, and instrumentation for large industrial gas engines.