WIN $5,000 For Your Mustang! Enter Now
Talk to a Mustang Expert
Mon-Sun 8:30 AM - 11:00 PM EST

Free Shipping On Orders Over $49. Details

Flowmaster American Thunder Cat-Back Exhaust (99-04 GT, Mach 1)

Market Price $570.99 You Save 13% ($75.02)
Our Price


FREE Shipping
  • Item 18410
  • MPN# 17312

In Stock Ships same business day. Choose options to add to cart

Features, Videos & Details

  • Aggressive Flowmaster Sound.
  • Super 40 Series Mufflers.
  • 3" Polished Stainless Steel Tips.
  • Mandrel-Bent Tubing.
  • Durable Aluminized Steel Construction.
  • Fits 1999-2004 GT, Mach 1, and Bullitt Mustangs.

Review & Installation Video

Hi I’m Justin with, and I’m breaking down Flowmaster’s American thunder Cat-Back exhaust fitting the 99-04 Mustang GT and Mach 1. A few of the big points with this catback are the 2.5” aluminized steel mandrel bent tubing, the 3” brightly polished OE style tips, and finally and most importantly, Flowmaster’s super 40 series mufflers which give this kit its very aggressive and unique sound. Flowmaster does offer a full stainless version of this same exact exhaust, which will be slightly lighter and better at resisting corrosion, however it does come with a slightly higher price tag. Due to the design of the factory exhaust you will need to cut it off in sections using a saw or something similar. Once you get that out of the way, the American Thunder bolts directly to your factory Mid Pipe, in about 2 hours using some basic hand tools and the included clamps. Now let’s hear how Flowmaster’s American Thunder sounds compared to our factory exhaust.

Flowmaster Sound.The Flowmaster American Thunder Cat-Back exhaust system with its mandrel bent tubing will greatly improve your 1999 to 2004 Mustangs exhaust flow for an increase in power, and their included Super 40 Series Mufflers will improve your exhausts sound for a deeper throatier muscle car exhaust note.

Quality Construction. Constructed from mandrel bent 2.5" 16 gauge aluminized steel tubing for it's corrosion resistant properties the Flowmaster American Thunder Cat-Back features their Super 40 Series chambered mufflers with 3.0 " diameter OEM style polished stainless steel tips for great muscle car looks and sound.

Fitment. This Flowmaster American Thunder Cat-Back exhaust system is specifically designed to fit the 1999-2004 GT, 2001 Bullitt, and 2003-2004 Mach 1 Mustangs for both impressive looks and sound. This system will not fit the SVT Cobra Mustangs.

Fitment: 1999 2000 2001 2002 2003 2004 Details

What's in the Box
  • (1) Right muffler assembly
  • (1) Left muffler assembly
  • (1) Right tailpipe assembly
  • (1) Left tailpipe assembly
  • (2) Clamps
  • (4) Lock Washers
Installation Info
Tech Specs
Cat-Back Exhaust Specifications
Piping Material: Aluminized Steel Tip Material : Polished Stainless Steel
Piping Size: 2.5" Tip Size: 3.0"
Muffler Type: Chambered Fitment: 1999-2004 GT, Bullitt and Mach 1 Mustangs
Will it fit my Mustang?
  • Bullitt - 01
  • Mach 1 - 03, 04
  • GT - 99, 00, 01, 02, 03, 04

Fits GT, Mach 1, and Bullitt

People Who Bought This Item Also Bought

Most Helpful Reviews

Sounds mean!

I previously had a BBK O/R X pipe with SLP Loudmouths and they were stupid loud. I wanted to choose a system that wasn't too loud but had a nice, mean tone... and this was the one! Sounds mean with a nice ...

Read More
Helpful (2)

Great sound

I had the magnapacks but decided to go with the flowmaster cat back. I feel that flowmasters make the best sounding exhaust for any mustang. Love the color black, installed with no problems. Thanks am ...

Read More
Helpful (2)

Overall Rating 4.7 out of 5 stars
Read All 100+ Reviews

Customer Photos (25) Submit Your Photo

View All 25 Photos

You Might Also Like

18 Questions / 8 Answers

Ask a Question

SOUND How is the American Thunder Catback sound going to be if we installed with BBK headers and BBK X pipe ? Because i have bought these headers and the x pipe and the cat back not yet so i am just asking before get that cat back any recommends for the cat back? Thank yall


Helpful (7)
  • that is what i have on mine, flowmaster/BBK headers/xpipe w cats... but calling them cats is a stretch. can get loud with your foot in it but what a great sound. its what a mustang should sound like. i daily drive and love every mile behind the wheel.


Show 1 more answer

V6 would this bolt onto a v6


Helpful (6)
  • The GT catback exhausts can be installed onto a V6 only when doing a dual conversion. You would need the V6 dual exhaust adapter in order for this to bolt up - without the adapter, the catback would not fit. I've included the adapter below so you can take a look. If you have any additional questions, please give us a call!


Show 2 more answers

Is there a way to get this without the super 40's? When I got my mustang it had already had super 44's on there and I love that sound. Would I have to replace the super 40's with my super 44's? Or is there another way to go about getting this cat-back without the super 40's?


Helpful (0)

Will this cat back fit perfectly with the Pypes off-road H pipe ?


Helpful (0)
  • Well, the piping size is identical between the two products, however they aren't necessarily designed to work with each other, so you may need a small modification to make it work if any at all, but it will be generally a simple install.


I have an 01 GT with BBK long tube headers and a BBK Offroad X-PIPE. My question is, will my setup bolt right up to the cat back exhaust without any cutting or welding? I'd really like to just put my GT on some jack stands and finish the job myself.


Helpful (0)
  • This will have no problems with fitment with your build as long as the BBK mid-pipe is a 2.5" tubing.


I need to install catalytic converters into my exhaust, would i be able to make the adjustment with this catback? or what are my options?


Helpful (0)
  • A catback exhaust does not have catalytic converters in it. The catalytic converters are located in the mid pipe.


More Products You Might Like

Customer Reviews (100+) Write a Review

Overall Rating 4.7

out of 5 stars

Installation Time:Full Day

Installation Cost:$100-$250

  • Loudness / Volume 4.297873 4.3
  • Exhaust Note 4.645161 4.6
  • Fit & Finish 4.361702 4.4
  • Bang For Your Buck 4.606383 4.6

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    September 26, 2015

    Music To My Ears!

    I'm thrilled with the sound and look of the Flowmaster American Thunder Catback exhaust system! The first time I turned the key and heard that melodius growl, it was Heaven on earth! I had spent quite a bit of time reading all the reviews of all the systems AM had to offer and was looking for a setup that wouldn't be ridiculously loud, and still derive some pleasure knowing that the "Beast" had awakened. Needless to say this system met all my expectations. It arrived within a few days of ordering, and couldn't wait to have it installed. Normally, I wouldn't hesitate to have installed it myself, as a great amount of reviewers mentioned how easy it was to install. However, age wise my back no longer permits me to crawl underneath. So the repair work I undertake is above ground level. All in all, I couldn't be more happier with this system. Looks great and sounds great! Thanx AM.


    Year: 2001 Submodel: GT Tewksbury,MA

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    July 27, 2013

    Sounds mean!

    I previously had a BBK O/R X pipe with SLP Loudmouths and they were stupid loud. I wanted to choose a system that wasn't too loud but had a nice, mean tone... and this was the one! Sounds mean with a nice tone! Even with the o/r x I have its not too loud. If you're looking for an exhaust that sounds great,looks great and has the famous flowmaster sound then here it is!


    Year: 2001 Submodel: GT Chicago, IL, USA

    Helpful (2)

  • 4/5

    Installation Time: Afternoon

    December 04, 2011

    Not as loud as "American thunder" would have you think

    I was expecting it to be a bit louder. The sound is very plain. But i believe it is worth the money. I would rather something a little throatier but it is good enough. I did not notice a difference in power.


    Year: 2002 Submodel: GT Louisiana

    Helpful (2)

  • 5/5

    Installation Time: Afternoon

    October 09, 2011

    01 V6

    My exhaust fit perfectly, and installed in a few hours with no tweaking at all. Pipes hang flat and level. Tips stick out about a half inch on each side, nice and even. I welded my exhaust at the muffler. I am not quite sure I like the sound while cruising, BUT OMG it sounds awesome above 2,000 rpms and under hard acceleration! I also, as other have, strongly recommend this for any V6 owner considering a dual exhaust conversion


    Year: 2001 Submodel: V6 Watertown, SD

    Helpful (3)

  • 5/5

    August 04, 2011

    Great sound

    I had the magnapacks but decided to go with the flowmaster cat back. I feel that flowmasters make the best sounding exhaust for any mustang. Love the color black, installed with no problems. Thanks am for another great service.

    Anthony E

    Year: 2002 Submodel: GT

    Helpful (2)

  • 5/5

    April 29, 2011

    V6 Mustang

    This is a great exhaust for any of you with a V6 looking to put a true dual exhaust system on your Mustang. It sounds great, and has a low deep rumble. The install wasn't bad at all. I pulled it up on ramps and put jack stands under the rear. Just make sure you buy the pypes exhaust hanger kit available from, if you are putting this on a V6 because you will need the GT style hangers for this exhuast. I took it to a muffler shop to have the pipes welded to the mufflers because it was hard to get the clamps tight enough. If you have a V6 Mustang, I would definitely recommend this exhaust for anyone looking to upgrade.


    Year: 2002 Submodel: V6

    Helpful (4)

  • 5/5

    April 13, 2011


    I installed this catback system on my 03 mach 1 and I couldn't be happier. Install was extremely simple, anyone could do it. It has a nice deep rumble like a mustang should. Not raspy and annoying. Would recommend this system for anyone who wants to turn heads.

    jacob petersen

    Year: 2003 Submodel: Mach 1

    Helpful (2)

  • 5/5

    June 22, 2010

    2000 rpms = :D

    Awesome exhaust. Perfect sound. Intalled myself and i wish i would have lined everything up perfectly before welding, it hangs a little low but thats my fault. Glad i went with these.


    Year: 2000

    Helpful (5)

  • 5/5

    January 10, 2010

    v6 mustang

    Very very happy with this exhaust, I first got the mac O/R H with SLP loudmouth 1 exhaust...big mistake, it was way too loud, and not a good loud. switch to this exhaust and it sounds perfect. good and deep, not raspy and not a tuner sound. I would recomend this for ANY v6 stang looking for duels.


    Helpful (75)

  • 5/5

    Installation Time: Afternoon

    September 27, 2011

    the pipes were good sound like thunder!!!!!!

    I will recomennd the pipes to anyone. Great fit only took me about 1 hour to put in.....


    Year: 2002 Submodel: GT Minnesota

    Helpful (4)

  • 5/5

    March 12, 2010

    American Thunder

    Just had this installed on my 2003 Mustang GT Convertible, this was exactly the sound I was going for. If you're like me, and don't want your car to sound ridiculous like some exhausts, then this is the one for you. I previously had Borla Stingers installed for about 15 minutes, and it was just stupid loud, didn't even sound cool to me, just stupid loud. This exhaust is one of the best I have heard, because I just wanted something louder than stock, but not obnoxiously loud. When you get on it it sounds great, but also sounds great just cruising, but you can put it up in a higher gear and it will get quieter, and there is some drone on the highway, but nothing too bad. I can't believe people actually like straight-through pipes, it would just be a constant drone, and annoying sound all of the time. I would highly recommend this exhaust, and I got the Stainless Steal version, great fitment, and a great quality product unlike others.


    Year: 2003 Submodel: GT

    Helpful (29)

  • 5/5

    January 22, 2010

    great sound

    This is a great sounding exhaust not overpowering loud but just loud enough. Sounds great when you get on it.


    Helpful (14)

  • 5/5

    Installation Time: Afternoon

    October 26, 2011

    True muscle car sound like no other!

    The American Thunder catback exhaust system is an easy bolt on kit that adds substantially more horsepower and an engine tone that is truly amazing. Installation is very simple, with only four bolts and a few exhaust hangers to deal with, meaning this mod will only take an hour or two. The result of the less restrictive 2.5" pipes (compared to stock 2.25") combined with a pair of Flowmaster Super 40 mufflers and 3" chrome exhaust tips is a sound that will turn heads! The deep, muscle car growl produced by this kit is loud enough to please any car enthusiast but not so loud that they annoy others on the road. The Flowmaster American Thunder catback exhaust system adds an excellent amount of horsepower and a sound that will draw a lot of attention to your Mustang with as little as a few hours labor and the use of common hand tools. A must have for anyone who wants to add a little more muscle to their muscle car!


    Year: 2004 Submodel: GT Mobile, Alabama

    Helpful (23)

  • 5/5

    June 29, 2010


    wow i got this system at 10 in the mornin, stalled a little then finally started assembling it at 3pm and was done by 7! wouldve been done at 5 if i didnt have to take the mufflers back off and drill some of the hole out on the right muffler connecter! overall im more then happy with this exhaust, its amazing and i would reccomend this to anybody that likes a nice smooth, deep tone but not overly loud car!


    Helpful (12)

  • 5/5

    January 18, 2011

    more that satisfied

    Just installed on my 2000 vert gt, more than happy with the low rumble and subtle backfire, noticable slight gain in power (untuned) in mid rpm range. Could be a tad louder, can easily be fixed with a midpipe.


    Year: 2000 Submodel: GT

    Helpful (9)

  • 5/5

    May 01, 2011


    The only thing that I am disturbed with this product, is they do not come with bolts to connect the joints. So when you take off the stock exhaust and your bolts break because of rusting you will be going to the nearest hardware shop.

    Brandon Morris

    Year: 2004 Submodel: V6

    Helpful (6)

  • 5/5

    Installation Time: Afternoon

    December 15, 2011

    Sound Great in the V6

    i have a 00 V6, and wanted to get some muscle car tone out of her. I took a chance and bought the pace setter h pipe and these bad boys... I was shocked with the upgrade in take off and sound.. My V6 doesn't sound like a V8 would with a full exhaust, but if deff sounds like a muscle car. Much better than i expected.. deep tone, and pretty throaty.. nothing like a ricer, so any V6 owner looking for an upgrade.. here is the answer to all your problems.


    Year: 2000 Submodel: V6 CT

    Helpful (4)

  • 5/5

    January 18, 2011

    Sounds great!!

    This is the perfect exhaust if you're looking for a nice deep rumble! Sounds great inside and out. Took less than 1 hour to install without any problems at all. Very happy with this purchase and would recomend to anyone looking to get more noise out of their stock v8!


    Helpful (4)

  • 5/5

    December 11, 2010

    Nice System

    Very nice system with the high quality you would expect from FloMaster. Not too loud but a very nice sound and no drone at highway speed. I highly recommend this system.


    Helpful (4)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: 0-$100

    June 28, 2013

    How to enhance your Stang!

    Just get this Flowmaster American Thunder Catback Exhaust matched with a Magnaflow Tru-X X-Pipe, and you'll relive that pleasure you had the very first time you drove a Mustang! You are gonna fall in love a second time with your car. You can't get a better sound, quality or satisfaction than that. Simply the ultimate Mustang sound. And if you need any help, call the AM team... tell them what you need, and the result you'll get is a PERMA-PRESS smile on your face.


    Year: 2003 Submodel: GT Montreal, QC, Canada

    Helpful (3)

Related Mustang Categories