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NGK Iridium IX Spark Plugs - Heat Range 6 (03-04 Cobra; 07-14 GT500)

Item 525003
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Market Price $79.99 You Save 13% ($10.00)
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$69.99 (set of 8)

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Ship to: Ashburn - 20149
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    Features & Details

    • Perfect for Stock Boost
    • Iridium Tip for a Constant Stable Spark
    • Improves Fuel Economy and Lower Emissions
    • Heat Range: 6
    • NGK Part# TR6IX; NGK Stock# 3689
    • 14mm Thread Pattern
    • Spark Plug Reach 0.690"
    • Fits 2003-2004 SVT Cobra and 2007-2014 Shelby GT500
    • Sold as a Set of 8
    High Performance. Keeping your Mustangs high performance engine running smoothly and efficiently is important, so routinely replace your old weak plugs with a new set of NGK Iridium IX Performance Spark Plugs for constant reliable spark power. The Iridium IX plugs from NGK will provide improved throttle response, fuel efficiency, lower emissions, and will reduce fouling.

    Superior Materials. NGK Iridium IX Performance Spark Plugs feature a copper core electrode for its superior conductivity and an iridium tip (which is 6X harder than platinum) for it's extremely high melting point, perfect for keeping your Mustangs high-performance engine running at it's peak. And as an added bonus the Iridium IX plug features Trivalent Metal Plating for it's superior anti-corrosion and anti-seizing properties.

    Application. This set of eight (8) NGK Iridium IX Performance "Heat Range 6" Spark Plugs are specifically designed for the 2003-2004 SVT Cobra and 2007-2014 Shelby GT500 Mustangs that are running stock boost.

    Fitment: 2003 2004 2007 2008 2009 2010 2011 2012 2013 2014 Details

    MPN# 3689

    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (8) Spark Plugs
    Installation Info

    Installation Time

    (approx) 2 Hours

    Difficulty Level:

    Light to Moderate mechanical skill required.

    Installation Guides

    Tech Specs
    Will it fit my Mustang?

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        Questions & Answers (5)

        5 Top Rated Questions

        Do these plugs come pre gaped from the factory? If not what is the recommended gap for 03 Cobra running stock boost?

        • Hello, These spark plugs do come pre-gapped, however it is always best to double check. The recommended gap should be listed in your vehicle's manual. According to NGK, these spark plugs come gapped at .040.

        Helpful (0)

        Would these be okay on a forged and strokes 2001 Bullitt on nitrous?

        • The NGK Iridium IX Performance Spark Plugs could work for your build, however considerably more information would be needed to best assist you, such as total horsepower, and the size of the nitrous shot being used. Please contact our Customer Service Department so that we may discuss your build and come up with the best suggestion for you.

        Helpful (0)

        I have heard the NGK V power plugs do not last very long. Will these be comparable but last longer?

        • Hello! These NGK Iridium IX Performance Spark Plugs - Heat Range 6 should last a long time, and are a very solid plug.

        Helpful (0)

        Will these work well with a 2001 gt, with kenne bell with 9psi of boost?

        • Thank you for your question about the NGK Iridium IX Performance Spark Plugs - Heat Range 6 (03-04 Cobra; 07-14 GT500). Unfortunately, these would not work for a 2001 GT with a Kenne Bell.

        Helpful (0)

        Are these one piece or two like the stock ones?

        • The NGK Iridium IX Performance Spark Plugs are two piece spark plugs.

        Helpful (0)
        Post Your Question

          Customer Reviews (5) Write a Review

          Overall Rating 5

          out of 5 stars

          Installation Time:Afternoon

          • Performance Gain 4.5 4.5
          • Fit 5 5

          • 5/5

            Installation Time: Afternoon

            April 12, 2019

            Great plugs

            Installed plugs with the JLT CAI, tune, 2.6 metco pulley and idler. They make everything run a lot better.


            Year: 2008 Submodel: GT500

            Helpful (0)

          • 5/5

            Installation Time: Less than 1 Hour

            July 13, 2018

            Worth there weight in gold

            These plugs improved my 2011 GT500 Shelby's throttle response, idel surging, and exhaust poping. I installed the Kennel Bell 2.8 LC Supercharger stage 3 kit. These plugs were the perfect choice for the increase in boost. Highly Recommend.


            Year: 2011 Submodel: GT500

            Helpful (6)

          • 5/5

            Installation Time: Less than 1 Hour

            January 16, 2018

            Best plugs yet

            Took care of my p0300. Pulls harder all the way to the red line.


            Year: 2003 Submodel: Cobra

            Helpful (8)

          • 5/5

            October 11, 2016

            Solved my problem!!

            I installed these plugs on my 10psi supercharged 03 mach 1 and solved my surging issues that were happening at cruising rpms (2k or less), I gapped them to 34 and have had no more issues. Thanks AM!!


            Year: 2003 Submodel: Mach 1

            Helpful (9)

          • 5/5

            Installation Time: Afternoon

            September 12, 2014

            Shelby plugs

            these took care of the misfire, detonation problems I was having with the upgraded mufflers and tune. runs much smoother and a bit faster. good call...thanks AM


            Year: 2011 Submodel: GT500 Tallahassee, FL, USA

            Helpful (9)

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