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Discussion Starter #1
Hi, i recently serviced my wee and discovered the installed IR plugs were cr 9 (the standard should be cr 8. They all looked quite nice and grayish, however, I proceeded and installed the standard cr8.
My question is what determines the plugs temp rating besides looking at their color?
For ex if the bike is used in hot countries, would it be wise to switch to a colder plug and vice versa?

Thanks.
 

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Generally, the length the ceramic portion of the spark plug's center electrode determines the temp rating. Some manufaturer's plug numbers are higher for the hotter plugs, some are lower. Go to the NGK website--they usually have a breakdown for the spark plug numbers and an explanation of those numbers. I think Nippon Denso does the same thing.
 

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FORUM GODFATHER.....R.I.P. PAT
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Plug temperature is pretty much unrelated to air temperature on a water cooled engine. A plug that is too cold will foul more easily and a plug that is too hot will erode its electrodes early. There is no reason to run a colder 9 plug with the possible exemption of racing the bike and always running it at high rpms.
 

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Discussion Starter #5
So from what I understand from your answers is stick to the recommended standard unless I observe anything unusual in performance or plug color?
 

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FORUM GODFATHER.....R.I.P. PAT
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:thumbup: You've pretty much got it. I wouldn't even bother looking. I'd put the stock heat range of Iridium plug in and forget about it for 50,000 miles unless the engine started to miss.
 

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Discussion Starter #7
Thanks guys
 

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...There is no reason to run a colder 9 plug with the possible exemption of racing the bike and always running it at high rpms.
Even then, the standard heat range plugs are fine. I endurance raced SV650's in the Texas summers, once doing a 6 hour race in 104F temps. No problems.
The riders, that was another story. :)
 
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