9 hours ago
(This post was last modified: 9 hours ago by SportsterDoc.)
The standard NGK stock number 6817 ($5.99 at O'Reillys 6 years ago, currently $10.49) is a nickel-copper electrode, rated for 30,000 miles.
The NGK stock number 91909 is an iridium electrode, rated for 100,000 miles. Probably not much performance difference, but a "lifetime" spark plug. Currently $17.99 at O'Reillys
Otherwise they are the same:
10mm threads
26.5 mm reach
9/16 (14mm) hex
heat range 8
Not seeing a difference between 90992 and 91909
The NGK stock number 91909 is an iridium electrode, rated for 100,000 miles. Probably not much performance difference, but a "lifetime" spark plug. Currently $17.99 at O'Reillys
Otherwise they are the same:
10mm threads
26.5 mm reach
9/16 (14mm) hex
heat range 8
Not seeing a difference between 90992 and 91909
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18 XVS950 22 Bonneville 20 CanAm Ryker
14 Honda CB1100 18 Yam XT250 16 MG V7II
17 Yam TW200 12 Bonneville 02 Sportster 1200S
03 Sportster 883 76 Honda CB750F 75 Honda CB360
70 Yam CT1 72 Yam CT2 72 Yam AT2 70 Honda SL350
70 Honda CL350 67 Honda CL160
67 Honda CB16062 Honda CA110