NGK marine spark plugs are designed to operate over a much wider heat range than ordinary plugs. Each NGK features high alumina ceramics for better heat transfer and electrical insulation. Patented triple gasket sealing process eliminates the possibility of combustion gas leakage. *They are resistant to carbon buildup and pre-ignition* Longer insulator nose prevents fouling and misfiring.* Solid copper core and nickel-tipped electrode provide a longer plug life.
Spark Plug Heat Range & Humidity NGK Spark Plugs Tech video
Here is a great video that talks about a spark plug heat ranges and humidity....read more
Does the compression ratio affect firing in temperature? When the compression ratio increases, the amount of pressure inside the cylinder also increases. This increase results in higher cylinder temperature because of the increasing temperature `with compression, it is very important to select the proper spark plug heat range. If the heat range is too hot, pre-ignition can occur which may cause major engine damage. If heat range is too cold, the spark plug insulator mass may fuel foul.