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NGK Iridium IX Spark Plugs - Heat Range 8 (03-04 Cobra; 07-14 GT500)

Market Price $99.99 You Save 10% ($10.00)
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$89.99 (set of 8)

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  • Item 64072

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    Features & Details

    • Perfect for Increased Boost
    • Iridium Tip for a Constant Stable Spark
    • Improves Fuel Economy and Lower Emissions
    • Heat Range: 8
    • NGK Part# TR8IX; NGK Stock# 3691
    • 14mm Thread Pattern
    • Spark Plug Reach 0.708"
    • 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) Two Heat Range Cooler NGK Iridium IX Performance Spark Plugs are specifically designed for the 2003-2004 SVT Cobra and 2007-2014 Shelby GT500 Mustangs that are running more boost.

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



    CA Residents: WARNING: Cancer and Reproductive Harm -

    What's in the Box
    • (8) Spark Plugs
      Hardware included:
    • None Required
    Installation Info
    Tech Specs
    Will it fit my Mustang?

      Customer Photos

        Questions & Answers (6)

        5 Top Rated Questions

        Ford racing 750 HP Kit I have 2012 Shelby GT 500 in the process of installing a ford racing 750 HP Supercharger Kit with long tube headers catted X Pipes and manga flow cat back system! Which spark plugs and coil on plug kits can I use to complement this setup Thanks

        • These NGK Iridium IX spark plugs are a colder than stock heat range on your 2012 GT500 and are recommended for an increased boost application.

        Helpful (2) Show 1 more answer

        I'm wanting to buy a 4.0 Whipple supercharger kit for my 2003 SVT Cobra Terminator. I'm needing help with what the best fitting heat range of NGK Iridium IX spark plugs to use? What type of roller cam I should use that would be capable of 800 to 1000 plus horsepower? Also is the Bama Live wire TS programmer going to be the best fit to use with this 4.0 Whipple charger? If not what would be the best compatible tuner to use that's going to give me the most horsepower and torque? Do you have any advise on an upgrade fuel pump? I also have a Borla Attack full cat back exhaust with long tube Hooker Headers. I could also use some greatly needed advise on upgrading my fuel injectors, like what size and brand would be best? I'm also going to be converting to an E85 methanol fuel tank and pump, what type of sensors do I need to go along with this set-up? Would you recommend that i use a 410 or 411 gearing? My goal is to have my SVT be not only a track car but also be a street car that i can use my programmer to change. Can you recommend a good traction and sub frame connector kit, along with a differential cooling kit and oil cooling kit. As well as any other information that you think is going to help me with getting the most safest and efficient system that will give me the most horsepower without blowing my engine and any other pertinent kits and systems so I'm not having to buy whole lot for separate items? Thank you for your time .

        im buy 4.0 whipple supercharger for my2003 svt termator help me on getting my cobra set up write itsx programmer what would give me the most house power plugs exspected to be cable of 800 pluse hourse power any advise on up grade fuel pump would be great help on cobra mustang what type of spark plugs would fit best with i also have borla attack ehaust and long tube hooker headers and i could take some greatly need advise i would like to up grade my fuel injectors do you have any advice on what size of feul injectors and brand

        I recently installed a 2.8 pulley and belt tensioner on my ‘04 Cobra, I have my Bama tune but not sure on what I need to do about my plugs. Do I need new ones or regap the stock plugs? If I need new ones what heat range do I need?

        • Spark plug selection will depend on your other modifications and horsepower output. As a general rule of thumb, you will decrease the spark plug heat range for every 100hp added to a supercharged, turbocharged, or nitrous vehicle.

        Helpful (0)

        What is the gap for a 2014 GT500 with a 2.4 Metco Pulley, a Ford Racing Cobra Throttle Body, and a JLT Big Air Intake with BAMA tunes?

        • We would recommend the stock gap for your GT500 for most applications, however, with the modifications on your vehicle, we would recommend using the gap which was specified when Bama programmed your tune.

        Helpful (0)
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        1 More Question
        Do these spark plugs plug and play or needs to be gap for gt500? 1 answer

          Customer Reviews (8) Write a Review

          Overall Rating 4.9

          out of 5 stars

          Installation Time:Less than 1 Hour

          • Performance Gain 4.625 4.6
          • Fit 5 5

          • 5/5

            Installation Time: Less than 1 Hour

            April 03, 2019

            2012 GT500

            Great plug. All came gaped correctly. Great performance from the plugs runs strong and no sputter.


            Year: 2012 Submodel: GT500

            Helpful (1)

          • 5/5

            Installation Time: Less than 1 Hour

            December 29, 2018

            Ngk spark plugs

            Highly recommend these spark plugs they do what the supposed to so no complaints


            Year: 2009 Submodel: GT500

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            June 06, 2018

            Plug and coil pack installation

            Noticable performance increase combined with Ford Performance coil packs.


            Year: 2003 Submodel: Cobra

            Helpful (7)

          • 5/5

            Installation Time: Less than 1 Hour

            May 28, 2018

            Great product!!!!

            Money well spent The plugs came with the proper gap, unlike others on the market. Where you have to re-gap at least 3or4 out of the eight.


            Year: 2011 Submodel: GT500

            Helpful (8)

          • 5/5

            Installation Time: Less than 1 Hour

            April 07, 2017

            Modified gt500 2010

            I added these plugs with a pulley/idler and cai tuner kit, as well as afco racing radiator and 170 thermostat. Very pleased with the responsiveness of the engine now and the plugs fit very well for the modifications done. Would recommend these plugs for anyone looking to do minor modifications to their turbo or supercharged mustang applications.


            Year: 2010 Submodel: GT500

            Helpful (11)

          • 5/5

            Installation Time: Less than 1 Hour

            January 04, 2017

            Amazing quality!!

            These Iridium Plugs really make all the difference! NGK is an awesome brand as always but once you start adding Boost and get a performance tune you'll notice that your car is gonna be running insanely rich and idle pretty rough. In my case I also noticed a small decrease in power as well because of my high altitude. I knew that I needed to get a better plug that would provide a stronger faster spark to be able to keep up with the new performance tune and added Boost. I purchased these NGK Iridium plugs with an 8 heat rating and it has definitely been a night and day difference! I have all my power back and my motor is running stronger and smoother than it ever has before! I've always been a huge fan of NGK plugs and they've never let me down. These new Iridium plugs have actually impressed me more than usual, if it's at all possible I feel that they have stepped up their game once again!!


            Year: 2007 Submodel: GT500

            Helpful (10)

          • 4/5

            Installation Time: Less than 1 Hour

            April 29, 2016

            Good product. Did not solve my pre ignition

            Good quality product made for smoother city driving. But i thought going down a few temperature ranges would solve my pre ignition problem under heavy load. Must be an intake temperature issue.


            Year: 2007 Submodel: GT500

            Helpful (10)

          • 5/5

            Installation Time: Afternoon

            February 07, 2016

            Very good but a little pricey

            I bought these a wile ago and they work amazing well. I was having some idling issues and these completely fixed that as well as adding to the responsiveness of my car. My only complaint is that they are a little pricey, other than that I love them. Great job AM!


            Year: 2003 Submodel: Cobra Corvallis, OR

            Helpful (10)

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