Denso Iridium Spark Plugs EJ25

Iridium: 8 times stronger than platinum, 6 times harder, and with a melting point 1200 degrees higher. New laser welding techniques make it possible to make a spark plug with an iridium electrode. The result is a plug that requires less voltage to spark, burns more of the fuel in the cylinder, and can spark at LEANER air/fuel mixtures (see inset diagram), resulting in higher horsepower and better gas mileage.

Although the plugs are expensive, you don’t have to change them as often as garden variety spark plugs. The iridium electrode is extremely resistant to erosion, so it can last MUCH longer than a normal plug. (Longevity will vary by usage, fuel mixture, and other factors.)

It’s the ultimate spark plug. Available in stock heat range, or one range colder for high boost (18+ psi) race applications.

Install note: The iridium center electrode is very thin. Unlike a conventional plug, you cannot gap the plug by sandwiching a gap tool between the electrode and the ground strap, then pushing on the ground strap. The hard electrode will dig into the gap tool, and when you remove the gap tool, you’ll break the electrode. Instead, adjust the ground strap by tapping it on a hard surface, or by pulling it gently with a tool; then measure the gap using your gap tool.

Set of four spark plugs.

Fits all EJ25 motors. Application list includes all 2006+ WRX, all 2004+ WRX STI, all 2004-2013 Forester XT, and all 2005-2011 Legacy GT.