Blown plugs result from bad bearings contaminating the element making them fail, lean mixture a more common cause, or poor quality plugs. An engine that's been run hot is one that's been run lean or improperly cowled (poor ducting) or both. If the plug element is distorted, crumpled, or melted, the cause is a lean run.
Too much nitro requiring too rich of a mixture will sometimes cause a plug to fail, but only because the extra fuel volume causes an overcompressed condition and usually crushes the plug element into the body of the plug.
Last edited by 1QwkSport2.5r; 09-12-2015 at 11:27 AM.