[THEFERMANATOR]

Some manufacturers will have 2 plug reccomendations for 1 engine depending on useage. Match the plugs to the engine and it's useage. If you idle alot you can normally run 1 heat range hotter, but you want to be carefull running a hotter plug at high rpm's as it can overheat and melt the plug and lead to detonation from the plug overheating. Omc used to reccomend surface gaps for engines run hard, and a long reach electrode for engines that idled alot. If you ran under varying conditions, you used a plug where the electrode was right on the surface to be in between. If in doubt, save an old set of plugs and carry a wrench to change them, and run the colder plugs. I would rather foul a plug than I would melt a plug and lose an engine. And if it's a dfi, make sure and index the plugs if it's reccomended. It's always best to have your firing gap pointing towards thecenter or towards the exhaust to minimize plug fouling.