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Old 02-02-2001, 12:20 PM
Posts: n/a
"Hot" and "Cold" spark plugs defined.

A "hotter" spark plug will not burn a piston. The heat range of a particular plug is determined by the volume of metal mass in the shell vs. the volume of ceramic around the core. A hotter plug, having more metal mass in the shell, will hold more heat and transfer less into the surrounding area of the cylinder and thus less to the coolant in the water jacket.

In lower performance engines, hotter plugs are typically found. These engines typically have less heat in the combustion chamber.

If the heat range is correct, the plug will burn off deposits at the correct rate and keep the plug clean. With the exception of a heavily modified engine, it is typically not only unnecessary, but also undesirable to stray away from the specified spark plug heat range.

My limited experience with the M103 engine has shown best results with the factory specified Bosch copper core plug, gapped at .038" or so. I now stay away from the platinums. The platinum has a very thin center electrode which generates a thin spark which contributes to poor idle quality.

Good luck,
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