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Tips on NGK Spark Plugs: The middle number indicates the heat range. The lower the number, the hotter the plug. The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling.

Spark plugs do not create heat, they only remove heat. The spark plug works as a heat-exchanger by pulling unwanted thermal energy away from the combustion chamber and transferring the heat to the engine's cool system. The heat range is defined as the plug's ability to dissipate heat.

Tips on spark plug gap: Check the gap on every plug prior to installation; plugs are NOT always pre-gapped at the factory. Always use factor recommendations for gap size, unless engine is modified. When checking gap, use only wire gauge; flat feeler or dial gauges do not accurately measure true width of spark gap.