There is a lot of confusion when it comes spark plug heat ranges. Many customers ask me for a "Hotter" plug assuming that this has something to do with the spark output. It does not. Spark plugs are made in different heat ranges & can be identified by the number stamped on the plug. The lower the number the hotter the plug generally but not always ie: Champion plugs are the opposite. The plug heat range determines thet temperature that the plug is designed to run at & has to be matched to the application. As you can see in the picture below the difference in heat range or the temperature that the plug body runs at is determined by the length of the heat path taken from the plug firing end to the cylinder head. If used outside of it's designed heat range the plug may foul or overheat. It doesn't effect the spark quality or engine temp in any way. Generally, there is never a need to alter the stock heat range unless the engine has been heavily modified.
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I have been involved in mechanics and motorcycling from a young age. I formed Cycle Improvements in 1981 and still have the same passion to learn today as when I started. Hope you find this blog interesting and educational.