Originally Posted by Cobra1

No knock sensors on a twin cam. Harley uses the plugs as sensors. Wrong plugs can cause issues.

Try the new NGKs if you want but don’t throw the old plugs away until your sure the engine runs the same as before. The ion sensing system will make funny things happen when it gets bad information.

Originally Posted by Notgrownup

I used the Screaming Eagle ones in my 07. They seem to last longer than stock. Just take them out brush them with some carb cleaner stray and put them back in…
I think they were iridium or unobtainium or something

Originally Posted by 60Gunner

One thing about NGKs is you don't have to use antiseize on the threads. In fact it's not recommended. Do that with the stock champions and you're liable to have the threads in the heads stripped out.
I've run nothing but NGKs and like hundreds and thousands of others, no issues with the ion sense.
I'm not even sure how people running the champions can say what the resistance is since they use a suppressor, not a typical resistor, and it can NOT even be measured with normal equipment.
Perhaps one of them that claim a certain resistance of the stock plugs can enlighten us as to how they determined what that resistance is.
This should be good for entertainment if nothing else.

Originally Posted by Glennstur

If I use Harley branded plugs I should use antiseize? - I saw you only mentioned champions. I am probably going to give the iridium number nines a try.

Originally Posted by 60Gunner

Yes. Harley branded plugs ARE champions and if you don't use antiseize they're likely to cause galling in the aluminum head and you'll strip out the threads in the heads. But don't use too much and cause firing issues!
I just run the normal NGK DCPR8E in my bikes. Part number 4179 with the solid tips. 4339 is the same plug but with screw on removable tips that tend to vibrate loose and can cause resistance issues.
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