The Spark Plug Myths Busted


When it comes to spark plugs people often talk about hotter or colder spark plugs, and it seems a logical assumption that a hotter spark plug somehow produces more power because the spark is hotter. But that's wrong. In fact race motorcycle engines actually require cooler spark plugs, and it has nothing to do with the spark.

Spark plugs, like catalytic converters, have an optimum working temperature of between 450 and 870 degree celsius. In this range they burn off contaminates that can build up and make it harder to produce decent sparks. If they go way above it the electrodes wear excessively, cause pre-ignition and in extreme cases melt completely.
By changing the shape and design of the insulator, engineers change the spark plug's ability to dissipate heat (remember the cylinder head is cooled, so heat flows from the plug to the head wherever they touch). Assuming the correct spark plug was installed as OE, and you tuned the engine – creating more heat, or the same heat but at higher revs – you may need to fit a cooler spark plug (i.e. one capable of dissipating heat quicker to stop its self over-heating). High-performance spark plugs are commonly built from harder exotic materials as the smaller electrodes (which spark more easily), wear more quickly.

Small and shaped electrodes all aim to reduce quenching (putting the flame out before it gets going by leaching its heat), and to move the spark as close as possible to the edge of the electrode. So now you know that hotter engines need cooler spark-plugs.
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