Re: 14mm Plugs
DB, I don't know what the plug should be for a stock engine, but yes, use a slightly colder plug with higher compression. It also depends on how you drive, highways vs. all rural roads or parades. Be sure the plug does not protrude beyond the threads in the adapter or you will have trouble removing the plug. In Champion plugs, I would suggest about a heat-range number of about 14 for your 6:1 head. (in a # N-14-Y, for instance, N is the thread size and length, 14 is the heat range, and Y is projected nose) The problem with Champion is they changed their numbering system several years back, so the plugs still have the above numbers but the boxes just show an unrelated, single number, so good luck at the parts store. 14 is a warm, mid-range plug.
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