The basic principles of spark plug design have changed little since their creation. Two contact points are positioned at a certain distance from each other, and an electrical discharge is sent through one of them to create an arc that jumps to the other point. This arc ignites the fuel-air mixture in a combustion engine. Dual-electrode spark plugs are merely a variation of basic spark plug design.
The main benefit that comes from having more than one ground electrode on a spark plug comes from increased longevity. A multiple-ground spark plug does not produce multiple sparks. The spark only jumps to the closest grounding point. As a spark jumps from the center electrode of a spark plug and contacts the ground electrode, a tiny bit of metal is removed from the electrode. Over time, this wear increases the gap between electrodes and increases the energy needed to cross the gap. With multiple electrodes, as one ground becomes worn, the spark naturally is attracted to the next closest ground, increasing how long it takes for the plug to increase in resistance as there are more grounds for the spark to connect to.
Multiple-ground spark plugs cannot be gapped. They are preset from the factory at the proper gap setting and require only that they be installed correctly and used in the correct applications. Because of their design and the fact that they are not meant to be gapped, engines that do not require multiple-ground spark plugs may not benefit from their installation and may even perform poorly if they are used.
Because multiple-ground spark plugs take much longer to wear out and increase in resistance, the overall reliability of the engine is improved. The engine will remain fuel efficient longer, start faster over its lifetime and lose less performance over time compared with an engine that uses only single-ground spark plugs.
