Designed specifically for the performance enthusiast, Iridium IX offers extreme ignitability, improved throttle response and superior anti-fouling. Why NGK Iridium? More Durability and a Higher Melting Point compared to Platinum, better center electrode anti-oxidation and anti-erosion, improved ignition, superior anti-fouling, lower required voltage, new metal shell plating process for better anti-corrosion. One Step Colder plugs are reccomended for cars with heavy modifications. These NGK plugs will get your Turbo Subaru running smoother and free up some power through increased efficiency and increased heat resistance. These are available in stock heat or one step colder for cars running approximately 100 horsepower more than stock. FEATURES: Fine iridium tip ensures high durability and a consistently stable spark Iridium alloy has extremely high melting point, perfect for today's high-tech, high-performance engines Trivalent metal plating provides superior anti-corrosion and anti-seizing properties Outstanding acceleration, high fuel efficiency and durability Ultimate design, technology and performance