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Types of Spark Plugs

Spark Plug layout

There are three things that make up a spark plug and its performance: the electrode gap, the materials used, and the heat insulation's efficiency. To understand why there are so many types of plugs on the market, you need to understand why these three things are important.

How a Spark Plug Works

Spark Plug LayoutSpark plugs receive electricity from the ignition coil and distributor. This power travels from the plug base, where the wire from the distributor connects, to the center electrode of the plug. From there, it jumps a gap to the side ground electrode.

In the process of the electricity flowing through the plug, the center electrode heats up enormously and becomes ionized, facilitating an easier spark jump across that electrode gap. The spark jumping across that gap is what ignites the fuel in the cylinder. Specific engines require a specific electrode gap distance, usually based on the size (width) of the cylinders being fired.

In order for the plug to work efficiently, the electrode gap must be just right, the materials must facilitate both the spark and electrical flow, and the insulation used must keep the center electrode at a specific heat under the type of electrical load it's given in the vehicle.

The Materials Involved

The materials used to make a spark plug vary from type to type because not all engines are the same. Factors such as the cylinder head temperature, the type of fuel used (and how "lean" it is), etc. all play into what type of plug is best suited for the vehicle.

The right plug not only ensures efficient operation, but can even be a deciding factor in whether the vehicle operates at all.

High-temperature engines, for instance, will require a cooler plug in order to maintain the right center electrode temperature. Conversely, cooler fuels (such as low-octane gasoline) will require plugs capable of higher heat in the electrode.

The type of driving also plays into this. Mechanics know that vehicles that do a lot of stop-and-go, short trip driving will require plug replacement more often than vehicles that drive long distances regularly. This is due to the heat factor almost exclusively.

Because of this, plugs use different designs (such as the single, double, or split ground electrode), different materials (such as platinum, copper, and ceramics) and are even of different lengths. All of this plays into what the plug is supposed to be doing and how well it is doing it.

Older vehicles almost always run well with standard copper plugs. Newer ones may see fuel economy or performance improvements with plugs made from differing materials to match higher-octane fuels being used. Late-model vehicles almost always have a specific plug design they're meant to operate with in order to reach peak performance and economy.

Spark plugs, while small things, are a big deal when it comes to engine performance and fuel economy!