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

Market Price $1,206.99 You Save 13% ($158.02)
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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
  • 2.5" 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 americanmuscle.com 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 americanmuscle.com, 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 2.5" 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?
  • GT - 15, 16, 17

Not compatible with Convertibles due to different bracing

People Who Bought This Item Also Bought

Most Helpful Reviews

American Thunder For Memorial Day

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

Helpful (1)

American thunder cat

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

Helpful (1)

Overall Rating 4.8 out of 5 stars
Read All 9 Reviews

Customer Photos (1) Submit Your Photo

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2 Questions / 1 Answers

Ask a Question

According to Flowmaster's website 817730 has 3" tubing not 2.5" I also have this Cat-Back Exhaust on my mustang and the OD of the pipe is 3.12" I just wanted to let you know that might have an error in you're description of this exhaust kit.


Hi, is this product 50-state street legal


  • Yes this product is 50-state street legal.


Helpful (0)

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Customer Reviews (9) Write a Review

Overall Rating 4.8

out of 5 stars

Installation Time:Full Day

Installation Cost:$100-$250

  • Loudness / Volume 4.111111 4.1
  • Exhaust Note 4.777778 4.8
  • Fit & Finish 4.333333 4.3
  • Bang For Your Buck 4.555555 4.6

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (1)

  • 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 (0)

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