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NGK Iridium IX LTR7IX-11 plugs are one heat range colder than stock, made for turbocharged Ford and Mazdaspeed engines running more boost. The fine iridium center electrode gives a stable, strong spark, and the trivalent metal plating resists corrosion and seizing in the head. They are a common first upgrade for Focus ST/RS, Fiesta ST, EcoBoost Mustang and Mazdaspeed owners. Compared with stock platinum plugs, they handle heat better under high boost; the trade-off is that they are not the right plug for a stock, low-boost car.
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Lowest price we've seen: $42.95 on Nov 13 at Amazon. Tracked across 1 store since Nov 13.
Owners of tuned EcoBoost and Mazdaspeed cars use these as a routine step-up plug and report smooth running under boost. Most criticism centers on having to gap them and on fouling when used on near-stock cars.
NGK Iridium IX spark plugs, part number LTR7IX-11, are sold as a set of 4. They are one step colder than the standard plug and are recommended for higher horsepower applications. A higher heat range number does not improve engine performance. It increases the plug's ability to dissipate heat.
Each plug has a fine iridium tip, and iridium alloy has an extremely high melting point. The tip is meant to give durable, consistently stable sparking, along with strong ignitability, improved throttle response and anti-fouling. Trivalent metal plating gives the plugs anti-corrosion and anti-seizing properties.
For stock turbo Mazdaspeed applications, gap the plugs to .026-.028. For applications over 500 hp, use a .024-.026 gap. The Ford Mustang GT needs 8 plugs, so order a quantity of 2.
