Elite spark plugs for the serious racer, the DENSO Iridium Racing best demonstrates its performance improvement during acceleration. Experience more power and torque, as well as increased engine efficiency and fewer misfires when ignitability is difficult. 0. 4mm Iridium-Rhodium alloy center electrode requires less voltage to fire and increases firing performance. 100% pure Platinum 0. 8mm ground electrode reduces risk of melting the plug during harsh racing conditions.