HKS Super Fire Racing spark plugs are high performance Iridium plugs designed to handle advanced levels of tuning and still offer easy start-up and smooth idling. By utilizing a 0.4mm diameter Iridium plug electrode core and a U-shaped grooved electrode, lower voltage is required for spark to occur. This delivers a stronger ignition spark, stable idle, and reduces the likelihood of misfire during high boost. Designed for performance tune and a heat range = 8. Price for a set of 4