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Old 08-15-2019, 08:59 AM   #3
tubman
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Join Date: Dec 2013
Location: Minnesota, Florida Keys
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Default Re: spark plugs 59ab

Asking NAPA might not be a good thing to do, because they will probably give you the number of a stock replacement, that will probably be incorrect. Make sure you have the proper thread length. Many aftermarket heads take longer than stock plugs. Stock heads take 3/8" reach plugs (Champion H series), while most after market heads I have seen use 3/4" reach plugs ("L" series Champion plugs). Too short a plug will be "shrouded", while one that is too long will interfere with the exhaust valve, causing a collapsed side electrode at best and engine damage at worst.

Perhaps someone on here has a more precise answer, but the make of plug is a personal choice, the length can be determined by screwing one into a head that's off the engine, but the heat range is best determined by experience. Edmunds heads have the spark plugs relocated so they can use extended tip plugs, but I think they are the only ones that can. resistor plugs are usually unnecessary, and the other variables are again, personal choice.
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