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As title I’ve had a DX that ran on NGK DCPR8E , Spark plugs but NGK site says the Muscle (which I now own) is DCPR9E? I know these run colder but why the difference as it’s the the same 1250cc engine ?

wondered if there was something I was missing ? As I have a set of DCPR8E have any muscle owners ran this part number ?
 

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As title I’ve had a DX that ran on NGK DCPR8E , Spark plugs but NGK site says the Muscle (which I now own) is DCPR9E? I know these run colder but why the difference as it’s the the same 1250cc engine ?

wondered if there was something I was missing ? As I have a set of DCPR8E have any muscle owners ran this part number ?
According to the HD manuals the plug is the same on every model be they 1130cc or 1250cc All models listed as 10R12A. Must be something wrong in their conversion chart.
 

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I don't have a specific answer but I do recall comparing V-Rod models years ago when I got my VRSCF 10 years ago! HP and torque were slightly higher for the Muscle than the others in the 2009 year. I would think our split pipes do not make much difference as they still are connected before going their separate ways to the rear.
So I am guessing here, but I'd say the map for bikes' tunes are different even though they have the same engine. I tired to find a quick answer on engine specs and found the link below...

 

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I don't have a specific answer but I do recall comparing V-Rod models years ago when I got my VRSCF 10 years ago! HP and torque were slightly higher for the Muscle than the others in the 2009 year. I would think our split pipes do not make much difference as they still are connected before going their separate ways to the rear.
So I am guessing here, but I'd say the map for bikes' tunes are different even though they have the same engine. I tired to find a quick answer on engine specs and found the link below...

If that were the case then HD would have specified a different plug which they don't. Only NGK could provide the answer to their reasoning.
 

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Coastrider, your logic makes sense! So now I wonder why NGK... Was it an error? SOBAD did say that the plug runs colder... And as far as the F having different specs?
 
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