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Flowmaster American Thunder Cat-Back Exhaust (15-17 GT Fastback)

Market Price $1,221.99 You Save 12% ($141.29)
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  • Item 384453
  • MPN# 817730

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    Features, Video & Details

    • Aggressive Flowmaster 60 Series Sound
    • Durable 409 Stainless Steel Construction
    • 3" Mandrel-Bent Tubing
    • 4" Polished 304 Stainless Steel Tips
    • Includes Two Flowmaster 60 Series Mufflers
    • Fits 2015-2017 GT Fastback Mustangs

    Review & Installation Video

    Review & Install Video

    Justin: Hey everyone, I'm Justin with and this is my quick look at the Flowmaster American Thunder Series Catback Exhaust System fitting your 2015 Mustang GT. Flowmaster's without a doubt one of the most recognizable names in the Mustang world or the muscle car world in general. In fact, we use several Flowmaster systems on some of our own project cars here at, including the Bama Terminator and also Project Coyote. All right, for all my Flowmaster fans out there you can expect that signature iconic Flowmaster sound from the American Thunder Series Catback here, thanks largely in part to the Super 44 Delta Series mufflers that are pretty much responsible for defining the Flowmaster brand through sound. Now, this system isn't going to be as loud as The Outlaw Series System for instance, but since it is a Catback and since you are deleting that suitcase factory resonator, you can expect a nice aggressive deep tone. In fact, Flowmaster says that the Super 44 Delta Series muffler is the deepest sounding highest performing two chamber muffler they've produced to date. The system consists of a durable 409 grade stainless steel for the construction while the Super 44 Series mufflers here have been coated with a black high temperature coating, a Flowmaster trademark to help resist any corrosion over the years. All the piping is all two and a half inch mandrel vent. On the tips themselves are four inch slash cut embossed with that iconic Flowmaster logo. Now, this would be a great time to tell you guys that the product page contains a ton of useful information such as customer reviews, detailed product specifics, and of course a detailed walk-through install guide. So if you're not already watching this on our product page, be sure to head back and click the link below. Speaking of that install, guys, I do want to tell you that the Flowmaster American Thunder Series Catback System is one of the few systems that you will have to cut to get installed. Now, with that in mind just make sure that you have all the right tools on hand, including a sawzall or something similar, along with a fresh metal blade and about two hours of your time to get everything bolted up. Again, if you have any questions whatsoever, you can always reach out to our team of Mustang experts by phone or email. They're always standing by ready to help a fellow Mustang owner in their time of need. Now, let's hear how the Flowmaster American Thunder Series Catback sounds compared to our factory exhaust.

    Classic Flowmaster Sound. Add the unmistakable Flowmaster sound to your Fastback S550 Mustang GT with an American Thunder Series Cat-Back Exhaust System from AmericanMuscle. This catback system improves exhaust flow using Flowmaster's 60 Series mufflers for that classic aggressive muscle car exhaust note your high powered Pony deserves.

    Stainless Steel Construction. Constructed from durable 3" 16 gauge 409 stainless steel tubing for it's corrosion resistant properties, the Flowmaster American Thunder Cat-Back features 60 Series mufflers with massive 4.0" diameter polished 304 stainless steel tips for impressive muscle car looks and sound. As an added bonus, the tips are embossed with the "Flowmaster" logo for true custom styling.

    Application. This Flowmaster American Thunder Series Cat-Back exhaust system is designed to fit the 2015-2017 GT Fastback Mustangs for both great looks and great sound. Not compatible with convertibles. Reuses the stock clamps for installation.

    Fitment: 2015 2016 2017 Details

    What's in the Box
    • (2) Muffler assemblies
    • (2) Pipes
    Installation Info
    Tech Specs
    Cat-Back Exhaust Specifications
    Piping Material: 409 Stainless Steel Tip Material : Polished 304 Stainless Steel
    Piping Size: 2.5" Tip Size: 4"
    Muffler Type: Chambered Fitment: 2015-2017 GT Fastback
    Will it fit my Mustang?

    Customer Photos (3) Submit Your Photo

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    2 Questions / 2 Answers

    Ask a Question

    does this system drone at speed


    • The Flowmaster system will have some drone to them yes.


    Helpful (1)

    Hi, is this product 50-state street legal


    • Yes this product is 50-state street legal.


    Helpful (0)

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    Customer Reviews (12) Write a Review

    Overall Rating 4.8

    out of 5 stars

    Installation Time:Full Day

    Installation Cost:$100-$250

    • Loudness / Volume 4.166667 4.2
    • Exhaust Note 4.833333 4.8
    • Fit & Finish 4.416667 4.4
    • Bang For Your Buck 4.583333 4.6

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      October 10, 2017

      American Thunder Cat Back

      I got my American Thunder cat back in 2015 I did not do a review doing one now I paid $989.00 for mine in 2015 I was sent 3" pipe and 40 series delta mufflers it was all new in box I was happy with the 3" and the 40 series the sound is still awesome now I have headers with no cats still sounds awesome keep up the good work Flowmaster and American Muscle


      Year: 2015 Submodel: GT

      Helpful (4)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      October 05, 2017

      2016 Mustang GT American thunder fatback exhaust

      This is what I needed to make my Mustang Sound like a Mustang with bite. I love the tone. It’s not too loud at idle but sounds off When you accelerate. Install was easy. Fit was perfect.


      Year: 2016 Submodel: GT

      Helpful (4)

    • 5/5

      Installation Time: Afternoon

      September 14, 2017


      Cam quick unharmed happy with it, it fit on just right had no problems with the product


      Year: 2016 Submodel: GT

      Helpful (3)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $100-$250

      July 03, 2017

      Sounds great!

      It sounds perfect. Not annoying to ride with, but a nice deep sound.


      Year: 2017 Submodel: GT

      Helpful (4)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: 0-$100

      May 26, 2017

      American Thunder For Memorial Day

      Just exactly what I wanted. Nice deep rumble, no rasp and a few HP


      Year: 2015 Submodel: GT

      Helpful (4)

    • 5/5

      Installation Time: Afternoon

      May 23, 2017

      American thunder cat

      The sound is awesome! Feels more responsive, deep tone through every gear. And easy installation 2 hrs


      Year: 2017 Submodel: GT

      Helpful (6)

    • 5/5

      Installation Time: Afternoon

      January 25, 2016

      The amazing flowmaster sound and performance

      Flowmaster always was one of my top choices in exhaust when I have owned a mustang. Classic sound and great performance. Installation took a little time but it was worth the work. Very satisfied! Great job American Muscle.


      Year: 2015 Submodel: GT New Orleans, LA

      Helpful (6)

    • 5/5

      Installation Time: Less than 1 Hour

      October 19, 2015


      This is a great way to open up your 2015 Mustang GT's exhaust. Very happy with the ease of installation. I would have given 5 starts on Fit and Finish, but it seems to be off to the right a bit. Tried numerous adjustments and can't seem to get it centered. Not horribly noticeable, but nevertheless off. It is going to take a little bit of bending of the hangers to get it right, but it will accomplish this when I install the Headers and weld it all together. Otherwise, if sound and quality is what you desire, then look no further!! Flowmaster is still the one when it comes to making your Stang a "STANG."


      Year: 2015 Submodel: GT Mount Dora, Fl

      Helpful (5)

    • 5/5

      Installation Time: Shop Install

      September 04, 2015

      Solid value and fun to drive

      I originally purchased the Flowmaster catback Outlaw series for my new 2015 GT pony. While amazingly deep and throaty it was also amazingly loud with a resonance between 1900 and 2100 rpms that made stereo listening or talking in the passenger compartment impossible. I replaced it with the Flowmaster American Thunder series and found exactly what I needed for pure driving pleasure. This series is still deep the throaty (although not so much as the Outlaw series) but has just amount of volume and 'thunder' to turn heads and make people wish they were driving the 'pony' instead of you. When you kick the gas pedal a little you really hear the pipes roar. I would recommend this series for anyone looking for daily driving fun with enough roar to turn heads in envy.


      Year: 2015 Submodel: GT Harrisburg PA

      Helpful (7)

    • 3/5

      Installation Time: Weekend

      August 03, 2015

      Used system

      I received a used exhaust system from American Muscle for a new price. Nothing was done by American Muscle to fix the problem. I would recommend buying this system else where.


      Year: 2015 Submodel: GT Belton,Tx

      Helpful (4)

    • 5/5

      Installation Time: Less than 1 Hour

      May 29, 2015

      Essence of a Mustang

      Great exhaust with a deep aggressive and distinctive growl. The x pipe adds to the volume without adding any drone which is perfect for longer drives. Installation was easy however there was no getting around cutting, was a bummer however not a deal breaker. Would go as far as saying, if you own the new Mustang 5.0 GT AND don't have this exhaust. for shame! All in all very pleased.


      Year: 2015 Submodel: GT Vaughan, ON

      Helpful (6)

    • 5/5

      Installation Time: Less than 1 Hour

      April 09, 2015

      Flowmaster American Thunder

      In love with this exhaust, couldn't be happier with my purchase. Very nice deep loping rumble at idle and really opens up when you get on it. Little to no drone at highway speeds. Love the sound while I accelerate at a normal rate, which is barely possible for me to do in this car, but you will know the people watching you just cruise off will just be begging you to punch it so they can hear it scream. If you want loud but just not sure quite how loud then I believe this is the exhaust for you. I was back and forth between this setup and the outlaw series and am definitely happy with this pick.


      Year: 2015 Submodel: GT Texas

      Helpful (4)

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