GReddy Spark Plugs are designed in cooler heat ranges to reduce heat and chances of pre-ignition. The reason it is so durable is the very fine, 0.6mm dia. Iridium electrode. Iridium Tune Spark Plugs are ideal for low to medium tuned engines, factory turbocharged engines or bolt on turbo kit equipped vehicles.
GReddy Spark Plugs use NGK heat range codes, so the larger the number the colder the heat range.