a buddy of mine put them in his street glide. he began experiencing problems with his engine running. he would not be able to rev above 3000 rpm. after tearing the top end down, he found that his oil pump gear had broken in half and one of the electrodes on the spark plug was missing. coincidence? maybe, but not one i'm willing to chance.
i'm not usually one to spout off with 'hd branded' stuff, but i do know that the ecm looks for the resistance value of the stock plugs in order to turn on the knock detector function. if the resistance is not correct, then that function doesn't work. but, there is no specification easily found for that value, and/or whether other plugs are 'close enough' to that value for it to work also. at 25,000 mile change intervals, i figure i'll spend the couple extra bucks for the hd plugs (long ways from those carbed days on my sporty where i would change them out every oil change

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