Improved Spark with Heat Range One Step Colder than Stock If you're starting to wonder if your RS or ST's stock spark plugs can handle the power of your tuned and/or modified EcoBoost engine, it's probably time to swap them out for something more geared for performance. These NGK Iridium IX spark plugs are a nice upgrade that have a one step lower heat range than OEM for heavily modified and tuned RS and STs that still feature NGK's legendary reliability and performance. The Iridium IX plugs are built from the ground up to resist corrosion and fouling while providing improved spark, reliability, and versatility over your RS or ST's factory spark plugs. This full set of eight iridium spark plugs from NGK are an excellent choice for tuned vehicles that have wore out the welcome of the factory plugs.
High-Quality Iridium Tip and Corrosion-Resistant Design The NGK Iridium IX spark plugs are named after their .6 mm laser-welded iridium tip that delivers a powerful arc while being highly resistant to corrosion and fouling. The insulator and electrode feature Trivalent metal plating that offers up vastly improved anti-seizure and anti-corrosion properties than traditional spark plugs. These plugs have a tapered electrode that reduces quenching while making regapping extremely simple.