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mppickett mppickett is offline
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Join Date: Oct 2005
Location: Barrington, RI
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The temperature of the spark plug relates to how much heat it conducts out of the combustion chamber. See this page for a great explanation:

Different plug manufacturers use different heat range numbers or letters in their designations. Even more confusing, some get colder as they increase and some get hotter as they increase. The hotter they are, the less likely they are to soot up and the more likely they are to cause engine detonation. Your goal is to find a heat range that doesn't soot up in normal driving and doesn't detonate when you are driving at full performance levels.

On my engine (roughly 425 flywheel hp) I use the NGK BKR7EIX plugs which are a couple of steps cooler than the NGK BKR9EIX plugs (CORRECTION, 7s ARE A COUPLE OF STEPS HOTTER THAN 9s IN THE NGKs). I'm dual plugged and it seems to be a reasonable range for my street use with occasional spirited driving. My choice was based on the OEM range of the twin turbos minus one heat range. It wasn't based on extensive trial and error.

Originally Posted by Flieger View Post
What does the heat range of a spark plug refer to? How does it relate to detonation?

Thanks for the schooling
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Last edited by mppickett; 03-22-2008 at 02:10 PM..
Old 03-20-2008, 03:34 PM
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