Quote:
Originally Posted by AnthonyG
To answer Frank, porcelain looks pretty good. 2000 + or - miles on them & their a nice toast color. I’m not sure whether 437 Autolites r extended but that what the ones shown r. Not sure the # of threads means anything as long as the arc pedipalp & ground hook r located ok. In this case as measured the arc pedestal is flush to the head chamber surface where it protrudes & the ground hook is entering approx .100” beyond the durface. There’s no indication the valves were bumping them after 2000 miles.
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As I said, the purpose of extend reach plugs, is to extend the life of them. It has nothing to do with the color that they burn, that a function of the A/F mixture. The extension of your plug, is similar to how far the oringinal H10 plug would be.
From your combustion chamber color, it does look like your engine is using some oil and extending them more, might make them last longer, into the future.
I would say that your heads are made for 5/8 reach plugs.