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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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      Product Information

      Features, Description, Reviews, Q&A, Specs & Installation


      • 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 -


      Customer Reviews (5)

      Write a Review

      Ratings Summary

      5.0 out of 5 overall rating from 5 customers

      Installation Time: Afternoon

      • April 12, 2019

        5 2008 GT500 - Rocky Installation Time: Afternoon

        Great plugs

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

        Helpful (0)
      • July 13, 2018

        5 2011 GT500 - 2011Shelbyman Installation Time: Less than 1 Hour

        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.

        Helpful (6)
      • January 16, 2018

        5 2003 Cobra - Jalani Installation Time: Less than 1 Hour

        Best plugs yet

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

        Helpful (8)
      • October 11, 2016

        5 2003 Mach 1 - Gmantj

        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!!

        Helpful (9)
      • September 12, 2014

        5 2011 GT500 - waveblastr Installation Time: Afternoon

        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

        Helpful (10)

      Questions & Answers (5 answers)

      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

      Installation & What's in the Box

      Installation Info

      Installation Time

      (approx) 2 Hours

      Difficulty Level:

      Light to Moderate mechanical skill required.

      Installation Guides

      What's in the Box

      • (8) Spark Plugs

      Tech Specs

      Will It Fit My Mustang

      • Cobra - 03, 04
      • GT500 - 07, 08, 09, 10, 11, 12, 13, 14

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