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Flowmaster American Thunder Axle-Back Exhaust (05-10 GT, GT500)

Item 18417
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      Review & Installation Video

      I’m Justin with and I’m taking a closer look at Flowmaster’s American Thunder Classic Axle-back exhaust for the 2005-2010 Mustang GT. The classic incorporates the tried and true 40 series muffler, which is the muffler that started it all for Flowmaster many years ago. Now this sound defined Flowmaster and is one of the more aggressive exhausts you can get from their lineup. The classic just like the standard American Thunder incorporates that same 16-gauge aluminized steel for its ability to resist corrosion and its overall durability. Now just like the American Thunder standard, the classic also features that very cool black finish for a stealthy look, however features a slightly larger 4” stainless tip embossed with that very cool Flowmaster logo. Getting the classic bolted up to your Mustang is a very straightforward task, and should take you only about an hour using basic hand tools. Now let’s hear how Flowmaster’s American Thunder Classic sounds compared to your factory exhaust.

      Product Information

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


      • Aggressive Flowmaster Super 44 Series Sound
      • Polished Stainless Steel 4" Tips
      • Durable Stainless Steel Construction
      • Includes Two Flowmaster Mufflers
      • Fits 2005-2010 GT, Bullitt and Shelby GT500


      Classic Flowmaster Sound. Give your Mustang that unmistakeable Flowmaster sound with a nice power boost with the American Thunder Axle-Back Exhaust System. This Axle-Back System improves exhaust flow using Flowmaster's patented chambered muffler design for that throaty, aggressive exhaust tone your high powered Pony deserves.

      Quality Construction. Constructed from durable 2.5" 16 gauge stainless steel tubing for its resistance to corrosion, the Flowmaster axle back features two special chambered Super 44 Series Flowmaster mufflers with 4" diameter polished stainless steel tips for muscle car looks and sound. As an added bonus the tip is embossed with the "Flowmaster" logo for true custom styling.

      This Flowmaster American Thunder Axle-Back Exhaust System is designed to fit the 2005-2010 Mustangs including the GT, Bullitt and Shelby GT500 for both great looks and great sound.

      Technical Note. Americanmuscle recommends adding the 2005+ Mustang 304 Stainless Steel Exhaust Hanger Kit from the drop down option above, to provide more strength, stability and a cleaner installed appearance. If you have a 2007 Mustang you may need the kit for correct installation.

      Fitment: 2005 2006 2007 2008 2009 2010 Details

      MPN# 817460

      CA Residents: WARNING: Cancer and Reproductive Harm -


      Customer Reviews (49)

      Write a Review

      Ratings Summary

      4.6 out of 5 overall rating from 49 customers

      Installation Time: Afternoon

      Installation Cost: 0-$100

      • March 07, 2020

        5 2008 GT - Ron Installation Time: Less than 1 Hour

        2008 GT 4.6 3Valve

        Minor cabin noise/buzz/moan around 1800-2000 rpm (60-65 MPH) in 5th gear (stick shift w/ 3.55 gears) while climbing hills, otherwise exactly what I was looking for.

        Helpful (0)
      • September 28, 2019

        5 2009 GT - JeffV Installation Time: Afternoon

        Great Sound

        Powerful sound. Great purchase. It took about three hours to install. I recommend.

        Helpful (0)
      • February 19, 2019

        1 2007 GT - BryanB Installation Time: Less than 1 Hour

        Quality has really gone downhill

        I remember when flowmaster products were deep, throaty and great sounding. This seems to be a thing of the past. These drone horribly between 1800-2000 rpm. They are only reasonably quiet at idle. They fitment wasn’t even close. I tried my best to get them straight, but ultimately had the local muffler shop cut and weld them into place. His quote was “how can a reputable company sell garage like this”. I’m putting my Roush extreme tailpipes back on after work today. No knocks on AM, but flowmaster has really been a complete disappointment

        Helpful (3)
      • July 24, 2018

        4 2008 GT - MarshallW Installation Time: Shop Install Installation Cost: 0-$100

        Old school. Sound

        Nice. Sound. For. My. 2008. Mustang. Gt. Reminds. Of. 1967. Mustang. S. Code. Installed. In. One. Hour.

        Helpful (3)
      • June 18, 2018

        5 2010 GT - RonD Installation Time: Less than 1 Hour

        Flowmasters Again

        This is my second set of these mufflers. We just bought a 2010 Mustang for my wife and the first thing she had to have were Flowmasters.

        Helpful (4)
      • December 27, 2017

        4 2010 GT500 - StevenM

        Flowmaster American Thunder

        I installed this exhaust on my 2010 Shelby GT500. On opening the box, I noticed that one of the tips was welded on slight off center. This was the second Flowmaster kit I purchased with this issue (first kit NOT purchased through American Muscle). I did not return it to American Muscle because, A- not their fault, B- it was not crazy crooked as the first kit was, C- I wanted this exhaust. Installed easy after jacking up back of car and I had to remove both brackets on each muffler to install. On MY car, the Flowmaster tips did not come out as far as stock. My main issue is that the DRONE between 1600ish and 2000 rpm is ridiculous!! Vibrates bit in the car. As my car runs at 1750 rpm at 80 mph, it’s kinda ( read Really Really) loud and distracting. Not figuring in the drone, the exhaust sounds AMAZING during start-up, idle and under acceleration. Tips look great, wish they stuck out another 2 inches. If I could go back in time, I would try the next quieter exhaust kit. I would still stick with Flowmaster, without a doubt.

        Helpful (3)
      • November 17, 2017

        5 2006 GT - Lukes06 Installation Time: Less than 1 Hour

        Never disappointed

        Sounds like I wanted it too. A little loud for the wife. But I love it.

        Helpful (3)
      • September 21, 2017

        5 2006 GT - JeffH Installation Time: Less than 1 Hour

        Jeff h

        Very nice sound... some drone, but awesome. Very easy to install.

        Helpful (3)
      • August 23, 2017

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

        Flowmaster Mufflers

        One of the best sounding mufflers on the market!!! The install was simple. I have Kooks long tube headers with Kooks catted x-pipe and the car sounds amazing with the Flowmaster mufflers!!! I have had many different mufflers on my GT500 and none sound as good as the Flowmaster American Thunder!!!

        Helpful (4)
      • June 01, 2017

        5 2005 GT - DonovanW Installation Time: Afternoon

        Sounds Tuff

        Good deep sound. Waiting for mufflers to burn out a little and get louder.

        Helpful (4)

      Questions & Answers (8 answers)

      5 Top Rated Questions

      Loudness meter?

      • The American Thunder will be more in the middle in terms of how loud they are. They will be quieter than the Outlaws, but louder than the factory exhaust. I'd say it's about a 5 or 6 out of 10.

      Helpful (0)

      Will they fit with long tube headers and an x pipe? If not then what full exhaust system do you recommend for a 05 mustang gt.

      • These would fit with long tube headers and an x-pipe but you would need over axle pipes as well to ensure a good fit. We usually recommend cat-back systems for long tube headers and x-pipe modifications to get the most out of your system. We do have the American Thunders in a cat-back system by Flowmaster here:

      Helpful (0)

      Have stock 07 GT, with Flowmaster Force II kit on it. How does this American Thunder kit compare to Force II Ford Racing FR500s? Want a little more V8 sound, but don't want one that's very loud and annoying to everyone else on the road. Seems like most kits are either too quiet or way too loud. Is there a kit in the middle? Thks!

      • The Flowmaster American Thunder Axle-Back Exhaust will be louder and more aggressive than the Flowmaster Force II and just slightly less aggressive and loud than the FR500S exhaust. The Flowmaster Force II will be the deepest most "muscle car" of the three.

      Helpful (0)

      Does this exhaust fit with the Roush Rear Valance

      • The Flowmaster American Thunder Axle-Back Exhaust is designed to git the 05-10 GT Mustang. The Roush rear valance utilizes a square cut out for squared tips.

      Helpful (0)

      what if you have 3" exhaust coming from headers, do they come in 3" or just 2 a half inch?

      • If your exhaust is 3" but the axle-back exhaust is 2.5" you will need to have it clamped down properly. However I would suggest purchasing an exhaust where the pipe size is 3" because you can be subjected to exhaust leaks or back pressure.

      Helpful (0)
      Post Your Question
      3 More Questions
      does this exhaust sound good on an automatic 1 answer
      How much HP gain will I get with this axle-back exhaust if I already have a BAMA Tune and K&N Air Intake? Also, is this one of the best axle-back exhaust in terms of HP gain? 1 answer
      exhaust So i have a X pipe daul exhaust on my 2008 v6 and i was wandering if i could put the flow master classic thunder gt mufflers on it? 2 answers

      Installation & What's in the Box

      Installation Info

      What's in the Box

      • (2) Muffler assemblies
      • (2) Clamps

      Tech Specs

      Axle-Back Exhaust Specifications
      Piping Material:Stainless Steel Tip Material :Polished Stainless Steel
      Piping Size:2.5"Tip Size:4"
      Muffler Type:ChamberedFitment:2005-2010 GT, Bullitt & GT500

      Will It Fit My Mustang

      • Bullitt - 08, 09
      • GT - 05, 06, 07, 08, 09, 10
      • GT500 - 07, 08, 09, 10

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