My home inspection of Speedmaster heads

12many said

So using a plug, if it existed, and of correct heat range that was longer to orient ideally would be the best option. Next would be to machine the bore so the standard length plug oriented ideally. Short of that maybe do some mild unshrouding and radiusing like being discussed is my take

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You can get longer plugs, but not in 14 X 1.25 thread that I know of. There may be some weird plug out there. Guess I could look and see.

With everything getting smaller, you are seeing 12 and even 10 mm stuff in automotive applications. Used to only see that stuff in motorcycle stuff and the like.

I'm not sure why they can't get the plug depth correct. It ain't that hard. Obviously, you'd want to lower the plug on the head of you can, but like I said, that may open up some other issues.

The best option is what everyone is doing...unshroud the plug and forget about the little bit of compression loss.