Look at this example of heat range. Notice it does NOT change spark plug reach. Has nothing to do with that. It changes the center electrode porcelain depth. Heat range is about heat transference. You can see in this small example, the hotter plug puts more heat into the chamber. The colder plug less heat into the chamber. Each has its own benefits depending on engine type and specs. But heat range hasn't a thing to do with spark plug reach. It's the depth of the porcelain around the center electrode.
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