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Flowmaster American Thunder Cat-Back Exhaust (15-18 EcoBoost)

Market Price $900.99 You Save 13% ($118.02)
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  • Item 389696
  • MPN# 817750

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Features, Video & Details

  • Aggressive Flowmaster Outlaw Series Sound
  • Durable 409 Stainless Steel Construction
  • 3" Mandrel-Bent Tubing - (Steps Up from 2.5")
  • 4" Polished 304 Stainless Steel Tips
  • Includes Two Flowmaster Outlaw Series Mufflers
  • Made in the USA
  • Compatible with Fastback and Convertible
  • Fits 2015-2018 EcoBoost Mustangs

Review & Installation Video

Review & Install Video

Hey everybody, I'm Justin with, and this is my detailed review of the Flowmaster American Thunder Series catback exhaust, available for your 2015 and up EcoBoost powered Mustang. You should be checking out the American Thunder catback from Flowmaster if you're after one of the loudest and most aggressive systems for your S550 EcoBoost, that also happens to be one of the most affordable. Now as you guys heard, you're getting every bit of turbo four-cylinder noise out of this system, from the loud and raspy tone, loads of turbo noise, even some pops and backfires on d-cell, so if you're into all that sort of thing, hang out with me for a little bit as we break this system down a little further. Sticking with the sound here a little bit more, since this is an exhaust, after all, now as you guys heard with your own two ears, this thing is going to deliver some pretty aggressive tone. In fact, probably one of the most aggressive systems I've personally heard for the EcoBoost cars. And that's going to be due to the Outlaw Series mufflers that are incorporated into the American Thunder Series catback here. We've had a ton of experience with this muffler here at AM, used it on a bunch of cars, and it's going to be one of Flowmaster's most aggressive systems they offer. Now again, you heard the sound clips guys, easy four out of five. I'm even willing to go up a notch and peg the scale here at a full five out of five on my one-to-five, or one-to-wake-the-neighbors scale. Again, if overall volume is what you're after, then this thing should be on your short list. Shifting gears away from the tone, guys, let's talk about the build with this thing here. Now even though the Flowmaster is traditionally going to be one of your more affordable options when it comes to EcoBoost catbacks, you're still getting a pretty solid build overall, 409-grade stainless steel throughout, including the 16-gauge tubing, starting off with 2 1/2-inch mandrel bends here at the Y-pipe before flaring up to a full 3-inch portion with the axle back section here. Now again, we are including the Outlaw Series mufflers with this system. They are finished off in the Flowmaster traditional black paint, and everything's exiting out the 4-inch slash cut tips, embossed with the Flowmaster logo. Now as you guys heard me say earlier, this thing is pretty affordable in the big picture, and that's pretty much true. It's going to be more of a value or entry level catback, landing you somewhere in the $700 to $800 range, and that puts it right in line with some of the MBRP and Gibson options here on the site. Now your next step up would be to go to a Stainless Works, for instance, or even a Magnaflow, even go to a BORLA, but all those options are going to ring you up for a $1,000-plus. When it comes time to get this thing bolted up to your ride, expect a very simple and straightforward job, guys, one out of three wrenches on my overall difficulty meter here, maybe an hour or two in the garage or driveway. Now no cutting, no permanent modification needed whatsoever, a full bolt-on job here at the Flowmaster. Now an extra set of hands would be nice, but not necessary, as that factory exhaust system is all one piece and can be a little cumbersome to drop by yourself. Other than that guys, though, everything is done underneath the car, so expect to have your race rams, jack and jack stands ready to go, or a lift before getting started. Simply put, guys, if you're looking to make a lot of noise for not a lot of money, then you'll definitely want to check out the American Thunder Series catback from Flowmaster, right here at

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

Stainless Steel Construction. Manufactured in he USA from durable 3" 16-gauge 409 stainless steel tubing for its corrosion resistant properties, the Flowmaster American Thunder Cat-Back features Outlaw 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 both fastback and convertible 2015-2018 EcoBoost Mustangs for both great looks and great sound. Reuses the stock clamps for installation.

Fitment: 2015 2016 2017 Details

What's in the Box
  • (1) Right muffler assembly
  • (1) Left muffler assembly
  • (1) Right tailpipe assembly
  • (1) Left tailpipe assembly
  • (4) Clamps
Installation Info
Tech Specs
Cat-Back Exhaust Specifications
Piping Material: 409 Stainless Steel Tip Material : Polished 304 Stainless Steel
Piping Size: 2.5" to 3" Tip Size: 4"
Muffler Type: Straight-through Fitment: 2015-2017 EcoBoost
Will it fit my Mustang?
  • EcoBoost - 15, 16, 17

Most Helpful Reviews

Flowmaster outlaw frees the pony

Very great buy. I was worried that the sound would be like a Honda or Toyota with aftermarket exhaust. But to much suprise my muffler guy said it reminded him of a small engine Ferrari. He expexted the ...

Read More
Helpful (3)


The price is right, the install was easy, and the sound is great! I love the sound at super low Rpms when you're in a parking garage, and stepping all the way on the gas when you're in a tunnel. Sounds ...

Read More
Helpful (2)

Overall Rating 4.3 out of 5 stars
Read All 9 Reviews

Customer Photos (2) Submit Your Photo

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9 Questions / 5 Answers

Ask a Question

Will this fit my convertible ecoboost?


  • This Flowmaster American Thunder Cat-Back Exhaust is compatible with both the convertible and coupe models.


Helpful (0)

Is the y pipe on this cat back the same as the flowmaster scavenger y pipe . So if I bought the axle back first and I wanna add sound then I got the scavenger y pipe with that fits the same as a cat back or it need modification


is this cat back system CA state legal?


  • Generally any cat-back or axle-back will be 50 state legal as it does not interfere with the stock cats. However California is very picky and we would suggest double checking with your local emissions center before purchase.


Helpful (0)

Does the cat back system delete the resonator?


  • Hi, Yes this cat back will delete the factory resonator.

    Chris J

Helpful (0)

Will it fits with my convertible ecoboost 2016 ??


  • This system is designed to fit both fastback and convertible model S550 Mustangs.


Helpful (0)

Is the exhaust loud inside the car?


  • Well this is definitely on the list of the loudest mufflers on our website so objectively speaking it has the best chance of being loud inside the car. However, if you're worried about drone specifically than yes, these Flowmaster Outlaws are a little susceptible to drone in high gear/low RPM situations.


Helpful (0)

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Customer Reviews (9) Write a Review

Overall Rating 4.3

out of 5 stars

Installation Time:Full Day

Installation Cost:0-$100

  • Loudness / Volume 4.75 4.8
  • Exhaust Note 4.75 4.8
  • Fit & Finish 4.375 4.4
  • Bang For Your Buck 4.75 4.8

  • 5/5

    Installation Time: Shop Install

    Installation Cost: 0-$100

    November 09, 2016

    Flowmaster outlaw frees the pony

    Very great buy. I was worried that the sound would be like a Honda or Toyota with aftermarket exhaust. But to much suprise my muffler guy said it reminded him of a small engine Ferrari. He expexted the pitch to get higher in the upper rpms but it did just the oppisite. The higher the rpms the deeper the sound. Great buy well worth the money. Easy install as well.


    Year: 2016 Submodel: Ecoboost

    Helpful (3)

  • 1/5

    Installation Time: Less than 1 Hour

    February 26, 2017


    The price is right, the install was easy, and the sound is great! I love the sound at super low Rpms when you're in a parking garage, and stepping all the way on the gas when you're in a tunnel. Sounds great and roars . Still sounds like a 4 banger to me but it's nothing like a Honda or Toyota. The only downside is that it comes in two pieces and you need to get them welded together if you have a convertible or else it will sag and contact a brace under the stang causing it to rattle. Perfect choice for me because I wanted something low priced and loud and this is what I got.


    Year: 2015 Submodel: EcoBoost

    Helpful (2)

  • 5/5

    September 05, 2016

    Everything I wanted!!

    Exhaust have such a huge performance boost for my ecoboost. So much louder and aggressive and makes a mustang really sound the way it's supposed to sound. Shipping was very fast and couldn't be happier.


    Year: 2016 Submodel: Ecoboost

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    June 28, 2016

    Noise is the killer

    The best cat back system I have ever purchased....


    Year: 2016 Submodel: Ecoboost

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    May 05, 2016

    THE NOISE!!!!

    Holy moly. I knew it would be loud but, man. So the install can be done solo with just some ramps and a jack. Not very easy but it can be done. The sound from this thing will wake the neighbors, the dogs, the cats, the dead you name it. Even though it's a four cylinder, the sound is definitely FLOWMASTER and good, deep and aggressive. A


    Year: 2016 Submodel: Ecoboost

    Helpful (1)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: 0-$100

    March 20, 2016

    Much Needed

    This is much needed to all Ecoboost owners who's trying to wake up there ride its loud its everything i wanted from my Ecoboost. The install was done by my local muffler shop cost about 85 bucks and took no longer then 2 hours, from the moment you turn on the car you will think you hoped in the wrong car because I didn't believe it myself, from the growl from the start to the screaming sound when you gun it this exhaust is perfect and at the perfect price range I would recommend this to all ecoboost owners that are looking to wake up there ride!!!


    Year: 2016 Submodel: Ecoboost

    Helpful (1)

  • 4/5

    Installation Time: Afternoon

    December 12, 2015

    Good value

    Installed by myself in the garage with car on jack stands in a couple of hours. Hardest part was removing the stock exhaust. I would definitely recommend a second person to help remove. Installation was straight forward but I did have to use a cone to fix one muffler inlet that was slightly bent in shipping. System was not packed very well. Tips were protected but that was all. I touched up the mufflers with black a paint before installing. Great sound and good price.


    Year: 2015 Submodel: Ecoboost Fort Worth, TX

    Helpful (1)

  • 5/5

    Installation Time: Less than 1 Hour

    July 20, 2017

    flowmaster catback

    took around an hour to do, very happy with it, only complaint is the the pipes were touch the sub frame.


    Year: 2016 Submodel: EcoBoost

    Helpful (0)

  • 4/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    March 07, 2017

    Great sounding Pipes

    The american thunder exhaust is a loud sounding, head turning, and great aftermarket exhaust for anyone looking to have their pony wake the neighbors or be recognized on the streets, from its idle rumble to the high rpm roar is really something to listen in person. I've listened to sound clips in deciding which exhaust to get but after going with these and finally getting to hear in person boy is it loud. I would've given a 5 but i was given 2 clamps instead of 4 clamps that was listed in whats in the box. other than that its worth it!


    Year: 2017 Submodel: EcoBoost

    Helpful (0)

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