Sportster/Buell Model: IRONHEAD XLH. Sportster/Buell Year: 1982. #3. 20 July 2005, 05:45. Originally posted by IronMick. I use NGK BPR6HS in the front cylinder, and NGK BPR5HS in the rear cylinder. The digit 6 or 5 is the heat range of the plug. For NGK plugs a smaller digit indicates a higher heat range. More @Wikipedia
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