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

Market Price $655.99 You Save 13% ($86.02)
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  • Item 18417
  • MPN# 817460

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Features, Video & Details

  • 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

Review & Installation Video

Review & Install 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.

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.

Application. 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

What's in the Box
  • (2) Muffler assemblies
  • (2) Clamps
Installation Info
Tech Specs
Axle-Back Exhaust Specifications
Piping Material: Stainless Steel Tip Material : Polished Stainless Steel
Piping Size: 2.5" Tip Size: 4"
Muffler Type: Chambered Fitment: 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

People Who Bought This Item Also Bought

Most Helpful Reviews

Nice upgrade.

I thought long and hard before deciding on purchasing the AT Classics. I read numerous reviews and watched every video I could find online. I can say I am happy with my choice. It took less two hours to ...

Read More
Helpful (8)

Great but not great

This axle back will get you tons of compliments and thumbs up as long as they never ride in your car. My car is a semi daily driver and these are way too aggressive for daily use. Especially with long ...

Read More
Helpful (4)

Overall Rating 4.7 out of 5 stars
Read All 43 Reviews

Customer Photos (10) Submit Your Photo

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5 Questions / 6 Answers

Ask a Question

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.

    AM MikeW

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)

does this exhaust sound good on an automatic


  • Yes it sure does!


Helpful (0)

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?


  • You really will not see any gain in horsepower with any axleback setup. There is not enough back pressure built up at that point in the exhaust to affect your performance. Axle back exhausts are strictly for sound purposes. For performance you will want to look into headers and a mid pipe.


Helpful (0)

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?


  • It might take a little hammering and bending but as long as the pipe diameters match up, then you should be fine. You might also have to hang your own brackets for the exhaust hangers though.


Show 1 more answer Helpful (0)

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Customer Reviews (43) Write a Review

Overall Rating 4.7

out of 5 stars

Installation Time:Afternoon

Installation Cost:0-$100

  • Loudness / Volume 4.432433 4.4
  • Exhaust Note 4.72973 4.7
  • Fit & Finish 4.378378 4.4
  • Bang For Your Buck 4.297297 4.3

  • 5/5

    Installation Time: Afternoon

    April 08, 2012

    Nice upgrade.

    I thought long and hard before deciding on purchasing the AT Classics. I read numerous reviews and watched every video I could find online. I can say I am happy with my choice. It took less two hours to install in my garage with a jack and a couple of jack stands. The hardest part was removing the stock mufflers and reaching a couple of the anchor point bolts along with aligning the tips. The larger outlets look great. And the sound...whoa the sound. They sound great at startup, deeper and louder that stock what a muscle car should sound like. Inside the volume is definately up compared to stock especally duing low rpm acceleration where I did notice some boom at first. It has lessened to a cleaner tone the more miles I've driven but it is still noticably louder than stock. Steady crusing at highway speeds is about as quiet as stock. I didnt see any mention of a power increase on the AM website. The Flowmaster website does include dyno graphs showing a Hp and torque increase. I have noticed a bit more power or maybe it just sounds faster:)


    Year: 2010 Submodel: GT Texas

    Helpful (8)

  • 5/5

    July 23, 2011

    Great but not great

    This axle back will get you tons of compliments and thumbs up as long as they never ride in your car. My car is a semi daily driver and these are way too aggressive for daily use. Especially with long tubes and an offroad x-pipe.


    Year: 2010 Submodel: GT

    Helpful (4)

  • 4/5

    Installation Time: Afternoon

    July 30, 2012

    Louder than stock

    I really ended up liking these, for someone in CA with sound and muffler laws. These are a great upgrade. Now when it comes to install, once the old mufflers are off its a breeze but to take off the stock is a bit of a pain but it can be done. Overall good exhaust not to loud but not quiet.


    Year: 2005 Submodel: GT CA

    Helpful (3)

  • 5/5

    Installation Time: Less than 1 Hour

    April 04, 2012


    Well I didn't buy them from here, got them from amazon. Since I buy a lot from here decided I'd put the review on here. Installation took me about 45 mins mainly because I didn't have the greatest car jack to use. But installation was easy none the less and I'm no mechanic. Bolted up nice and snug just like the stock ones. Sound was completely different. You can definitely hear that distinctive tone when you start it up and sounds amazing going through the gears ( I have an automatic). Sounds simply amazing. I definitely recommend this product. Best bang for your buck!!


    Year: 2008 Submodel: GT Chantilly, VA

    Helpful (3)

  • 5/5

    Installation Time: Afternoon

    March 14, 2012

    Deep Vibrating Baratone Bass... Mean!

    You won't go wrong with these Mufflers. The Fit and Install was perfect. And the Sound!!!! Deep, Vibrating Bass that will Move You and those around You. What are you waiting for? Buy these! They're Great!


    Year: 2008 Submodel: GT Central Jersey

    Helpful (3)

  • 5/5

    Installation Time: Shop Install

    September 24, 2011

    sounds great

    Gives it that great rumble and awesome tone. Great price for the product. Will be coming back for more.


    Year: 2005 Submodel: GT San Antonio, Tx

    Helpful (3)

  • 5/5

    Installation Time: Afternoon

    September 23, 2011

    Great Sound!

    I purchased the Flowmaster American Thunder Classic exhaust just 2 days ago and it has already arrived and been installed. I would say that I am pretty mechanically challenged and it took me about 2 hours for the install. After the install, I am very impressed. When I stand behind my car, I can feel the bass of the exhaust rumble in my legs. I have no problem with not being able to hear inside my car or hearing my radio over the exhaust (although I do have the Shaker 1000). I would highly recommend this product to anyone who wants the classic Flowmaster sound with some extra guts to it.


    Year: 2008 Submodel: GT Beltsville, MD

    Helpful (3)

  • 5/5

    August 02, 2011


    I got theses and installed them this past spring. The black finish isn't great. I had to prime/paint them with high temp paint. They are easy to install, with a lift. The sound is awesome and throaty.


    Year: 2009 Submodel: GT

    Helpful (3)

  • 5/5

    Installation Time: Afternoon

    December 29, 2012

    flowmaster classic axle back

    My 2010 GT sounds awesome .A lot of good compliments on sound, flowmasters look really good with 4" tips.highly recomend this classic axle back for any model year mustang.


    Year: 2010 Submodel: GT Lantana, FL, USA

    Helpful (2)

  • 5/5

    Installation Time: Afternoon

    September 01, 2012

    Wow,... What a difference

    First of all,.... I was amazed at the shipping/delivery. Can't promise this for everyone, but I placed my order with AM early one afternoon, and the FlowMasters were on the front porch the next afternoon! No problems with instalation at all, and that is with being very mechaniclly challenged, and having no lift or ramps. I had have to loosen the H pipe clamps after the mufflers were installed for the proper alignment, then of course tightening everything up again. The "sound clip" video does not do these mufflers justice. I know its hard to capture the sound on camera but thses are so much better in person. Strong, steady, aggessive sound during start-up, take offs, and shifting, but levels off for highway/interstate cruising. I am VERY pleased, with both these mufflers and AM !!


    Year: 2010 Submodel: GT

    Helpful (2)

  • 1/5

    Installation Time: Afternoon

    August 04, 2012

    Bad fit! fir 2010 Mustang Gt

    When having my put on my car by a local mechanic shop... They had to re-notch the driver's side muffler to make it fit on the exhaust pipe... I did call and talk to customer service at American Muscle and they did refund me the cost for the re-notching of muffler.... but the passenger side (same one they notched does not come out the exhaust slot on passenger side that it does on the passenger side.. I talked to the mechanic and he told me the end of the pipe that connects to the exhaust is welded on crooked and will needed to be heated up with the torch to make it fit evenly in the in exhaust slot on the Mustang where the tips fit. More cost for me! I think they put different year model axle back exhaust in the box...


    Year: 2010 Submodel: GT Alford, FL

    Helpful (2)

    • Response from AmericanMuscle

      This is the first we've heard of fitment issues with this axle-back. I'm sorry to hear you had these install problems, but glad we were able to help reimburse some of the additional shop costs for you!

      Lisa , Customer Care

  • 5/5

    Installation Time: Less than 1 Hour

    June 02, 2012

    Head Turners!

    I bought these for my wife's 09 GT convertible and i was concerned they might be a little too aggressive. After installing them and having a slight issue with the driver side muffler ( there is a bracket in the way and you cannot get the muffler hanger in without taking it off, i never heard anyone complain about it so it might just be a convertible only bracket) i was stunned about how it sounded at idle and revving it. Awesome sound. However, the 2k rpm drone in 5th gear on the highway is annoying enough to put in down in 4th to gain some sanity back. Again, this might only be a convertible issue seeing how a few reviewers said the 2k drone was no worse than stock. Sound awesome, but i would not consider putting them on a convertible.


    Year: 2009 Submodel: GT PA

    Helpful (2)

  • 5/5

    Installation Time: Less than 1 Hour

    February 06, 2012

    Easy Install=Amazing upgrade!

    I was prepared for this installation to take at least 2 hours. With the help of a friend, we were able to give my mustang a new rumble in about 45 minutes. Neither of use had dealt with exhaust installation prior to this evening, and this was as simple as it gets. I was afraid that there was going to be a drone while at normal highway and interstate speeds, but there has been neither. With the windows up at 70 miles per hour, it sounds like it did when it came from the factory. I am very pleased with the service and speed of delivery set up by American Muscle and I plan on doing much more in the near future.


    Year: 2010 Submodel: GT Alabama

    Helpful (2)

  • 5/5

    August 17, 2011

    So Deep!

    Put these on in place of the flowmaster 60 series axle backs and man what a difference. Louder, deeper, throatier you name it. Have a bassani o/r x with it along with shorty headers and a steeda CAI. Car is a beast and turn heads everywhere i go no matter what gear you are in. True old school muscle car sound. Nothing like flowmaster.


    Year: 2005 Submodel: GT

    Helpful (2)

  • 5/5

    Installation Time: Afternoon

    June 01, 2017

    Sounds Tuff

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


    Year: 2005 Submodel: GT

    Helpful (1)

  • 5/5

    Installation Time: Less than 1 Hour

    April 07, 2017

    Flowmaster AT

    I've had this same axle-back exhaust on three different Mustangs, and they sound great on all. Installation is simple, and the difference is amazing. Only issue I've had is the dreaded drone around 2K rpm. Other than that, they sound great.


    Year: 2008 Submodel: GT

    Helpful (1)

  • 5/5

    Installation Time: Less than 1 Hour

    October 28, 2016


    I'll start by saying these flowmasters have an awesome sound. Deep and mean sounding! The kit now includes super 44s vs the classic 40 series mufflers. I was after that classic hollow metallic fox body mustang flowmaster sound and the super 44s just aren't what I'm looking for. They sound more modern with a hint of the classic sound. Drone isn't too bad. Can still talk and hear the radio without issue. Quality is amazing. Look and feel like a great product. Easy install. I still give them a 5 star because they sound great and high quality. I was after a very specific sound and this didn't hit exactly what I wanted but if I hadn't gone in looking for something so specific I would be in love with these. I would say these have a modern mustang, camero, vette, challenger sound to them vs classic fox body.


    Year: 2007 Submodel: GT

    Helpful (1)

  • 4/5

    Installation Time: Less than 1 Hour

    October 27, 2016

    Love the sound!

    This axle back gives the car a very deep, aggressive tone and sounds great with hot rod cams. That being said, since it has such a deep note, there's a lot of drone at 1500-1900 especially in 5th gear with 3.31 gears. And the exhaust isn't that loud at high RPM either, but that's on a car with stock cats and manifolds. Overall its a good quality, good sounding chambered exhaust. No issues with fitment and the tips look great.


    Year: 2008 Submodel: GT

    Helpful (1)

  • 5/5

    July 23, 2016

    Great sound, bad packaging

    I received my exhaust on time and in a big box. When I opened it up the exhaust seemed to be in good condition, but the clamp to attach it the the pipes was bent as if it had been crushed. I ended up having to straighten then the clamp because I couldn't use the oem one since it was welded to the other muffler. Took longer than it should because of careless handling. Otherwise the sound is great and at 2k RPM it is amazing.


    Year: 2010 Submodel: GT

    Helpful (1)

  • 5/5

    July 15, 2016

    Great upgrade to 05 GT

    Great sound and one of the best mods you can do yourself in under two hours. Great perfomance gains. Not to loud like other have said. American Muscle is the best they are spot on in descriptions and videos. I am running an 05 GT with Air Aid cold air intake, new Flowmasters and Bama performance custom tune. Great buy! worth the money..


    Year: 2005 Submodel: GT

    Helpful (1)

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