Free Shipping On Orders Over $49. Details

Talk to a Mustang Enthusiast
M-F 8:30A-11P, Sat-Sun 8:30A-9P
Win $15,000!! Enter Now
Coronavirus: We are Open For Business, Prioritizing health and safety Learn More

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

Item 64072
Call a Mustang Enthusiast at 1-877-887-1105
M-F 8:30A-11P, Sat-Sun 8:30A-9P
Market Price $99.99 You Save 10% ($10.00)
Our Price

$89.99 (set of 8)

FREE Shipping

Will this fit your Vehicle?

Select a different vehicle Help?
Update or Change Vehicle
In Stock

Ship to: Ashburn - 20149
Sorry, please enter a valid US or CA postal code
We're sorry, zip can't be updated at this time.
    Create a list
    Add to New List

    Saved - View your saved items

    We're sorry. We couldn't save this product at this time.

      Product Information

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


      • 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.

      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

      MPN# 3691


      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (8)

      Write a Review

      Ratings Summary

      4.9 out of 5 overall rating from 8 customers

      Installation Time: Less than 1 Hour

      • April 03, 2019

        5 2012 GT500 - SteveSnow Installation Time: Less than 1 Hour

        2012 GT500

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

        Helpful (1)
      • December 29, 2018

        5 2009 GT500 - ChanceB Installation Time: Less than 1 Hour

        Ngk spark plugs

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

        Helpful (3)
      • June 06, 2018

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

        Plug and coil pack installation

        Noticable performance increase combined with Ford Performance coil packs.

        Helpful (7)
      • May 28, 2018

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

        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.

        Helpful (8)
      • April 07, 2017

        5 2010 GT500 - ElliotD Installation Time: Less than 1 Hour

        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.

        Helpful (11)
      • January 04, 2017

        5 2007 GT500 - Am2drag Installation Time: Less than 1 Hour

        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!!

        Helpful (10)
      • April 29, 2016

        4 2007 GT500 - Theblosse Installation Time: Less than 1 Hour

        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.

        Helpful (10)
      • February 07, 2016

        5 2003 Cobra - Jake Installation Time: Afternoon

        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!

        Helpful (10)

      Questions & Answers (5 answers)

      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 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 (1)

      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 .

      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)

      Do these spark plugs plug and play or needs to be gap for gt500?

      • The spark plugs do come pre-gapped; however, with any spark plug - these included - it is highly recommended that each plug be checked prior to installation to ensure that everything is as it should be!

      Helpful (0)
      Post Your Question

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (8) Spark Plugs
        Hardware included:
      • None Required

      Tech Specs

      Will It Fit My Mustang

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

          Related Mustang Categories