Spark Plug Heat Ranges

[ModelTWoods]

I know this has undoubtedly been discussed before, and I know too hot a plug can cause pre-ignition, and too cold a plug will not self clean, but when using a 14 mm plug in an iron cylinder head, is using too hot or too cold a plug dangerous in a Model T engine? I have a chance to buy some NOS Champion J-2 14 mm plugs (very cold) or some NOS Champion J-14 14 mm plugs (very hot). These are vintage plugs that look more like a Model T plug than current production plugs. I wish I could find some J-9 or H-9 which would be medium range plugs.

[Terry_007]

Those are not Model T plugs and certainly don't look like Model T plugs. Spend your money on the correct plug - Champion X 1/2" pipe thread.
Terry

[ModelTWoods]

Those are not Model T plugs and certainly don't look like Model T plugs. Spend your money on the correct plug - Champion X 1/2" pipe thread.
Terry

Terry Bond, I am looking for a vintage looking 14 mm plug to use in a Kevin Prus cast iron head. He only made these with the 14 mm size. I cannot use 18mm, 7/8" Model A, or 1/2" T plugs in a head drilled and tapped for 14mm plugs, and its not on a car that will ever be judged for points. If I ever switch heads back to the original T high head, I have Champion X and Champion A-25 plugs.

Since this head uses the plugs directly, without the need for adapters, I don't need a 14 mm plug with an extended tip.

[Kerry]

Too cold, no, the worst that could happen it oils up. Too hot, yes, could burn a hole in a piston.
Most stationary engines run a mid range of J8