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

Market Price $640.68 You Save 12% ($73.71)

$566.97

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  • Item 18436
  • MPN# 817312

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Features, Video & Details

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

Review & Installation Video

Review & Install Video

Hi I’m Justin with AmericanMuscle.com and I’m taking a closer look at Flowmaster’s stainless steel American Thunder Cat-Back exhaust, fitting the 99-04 Mustang GT and Mach 1. The two biggest features with this system are of course the full 409 grade stainless steel constructions throughout, and also the super 40 series mufflers, which give you that classic Flowmaster throaty rumble. The stainless steel tubing features a 2.5” diameter and mandrel bends throughout, all of which exists through these 3” hand polished OE style tips. Due to the design of your 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, getting the American thunder bolted up, is a pretty straightforward that should take you roughly 2 hours using some standard hand tools and the included clamps. Now let’s hear how the stainless 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.

Stainless Steel Construction. Constructed from mandrel bent 2.5" 16 gauge 409 stainless 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.

Application. This Flowmaster American Thunder Stainless Steel 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: 409 Stainless 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

Most Helpful Reviews

5/5
American Thunder

Another fine product from Flowmaster. Easy install with the right tools and a little patience you will have an amazing sound coming from your Mustang.

Helpful (1)

5/5

great product

amazing difference from stock. deep and more aggressive. would definitely recommend this for anyone looking for a deep tone.

Helpful (1)

Overall Rating 4.8 out of 5 stars
Read All 22 Reviews

Customer Photos (8) Submit Your Photo

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5 Questions / 7 Answers

Ask a Question

Could this fit on pypes catted x pipes on a 2004 v6

tonyv6

  • Absolutely! Installing the Pypes Catted X-pipe for the V6 will allow you to install any GT catback, including this Flowmaster American Thunder. Hope this helps!

    LisaS

    Good Answer (1) (0)

Show 1 more answer Question Resolved

Build Material The description states pipes and tips are stainless, what about the muffler itself?

Theweaverman

  • The entire catback is stainless steel. Flowmaster's made of aluminized steel are typically painted black.

    Tracy67

    Good Answer (0) (0)

Answer This Question I need this answered (0) (0)

Do these require Pypes Exhaust Hanger Kit I have a v6 & plan on getting the Dual Exhaust Adapter Kit to make the cat back installation possible. On the stock v6 bumper would you need the hanger kit?

Ceez92

  • Whenever tackling a new exhaust install, do yourself the favour and get a new hanger kit. Makes the job alot easier. Many shops will suggest providing them a new hanger kit as well, making their job easier, taking less time, saving you money.

    chriscarr86

    Good Answer (0) (0)

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Will this work with the MAC Ceramic Long Tube Headers #40062 and MAC Off-Road H Pipe #40064 on the V6?

Redwolf1155

  • The MAC Ceramic Long Tube Headers (94-97 V6; 01-04 V6), item # 40062, (http://www.americanmuscle.com/mac-ceramic-longtube-0104v6.html) will bolt right up to the MAC Off-Road H-Pipe (99-04 V6 w/ Long Tube Headers), item # 40064, (http://www.americanmuscle.com/mac-or-shorty-hpipe-9904v6.html). Though, this H-Pipe may not bolt directly to the Flowmaster American Thunder Cat-Back Exhaust. This Cat-Back is designed for a GT. We cannot guarantee fitment of this item on a V6. The H-Pipe and Cat-Back have the same piping size of 2.5", but you may need to do some modifications to make them work together.

    AshleyK

    Good Answer (0) (0)

Question Resolved

will this work with the pacesetter v6 h-pipe ?

krash

  • Yes. The addition of the PaceSetter V6 Dual Exhaust Adapter Kit (99-04 V6) (Item #51063) allows any of the GT cat-backs to work for your V6, so yes you will be able to install the Flowmaster American Thunder Cat-Back Exhaust - Stainless Steel (99-04 GT, Mach 1)

    JeffAM

    Good Answer (1) (0)

Answer This Question I need this answered (0) (0)

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Customer Reviews (22) Write a Review

Overall Rating 4.8

out of 5 stars

Installation Time:Afternoon

Installation Cost:$100-$250

  • Loudness / Volume 4.578948 4.6
  • Exhaust Note 4.736842 4.7
  • Fit & Finish 4.631579 4.6
  • Bang For Your Buck 4.473684 4.5



  • 5/5

    July 28, 2016

    American Thunder

    Another fine product from Flowmaster. Easy install with the right tools and a little patience you will have an amazing sound coming from your Mustang.

    frank

    Year: 2003 Submodel: GT

    Helpful (1) (0)

  • 5/5

    Installation Time: Afternoon

    August 02, 2013

    great product

    amazing difference from stock. deep and more aggressive. would definitely recommend this for anyone looking for a deep tone.

    AlexAM

    Year: 2001 Submodel: GT Aston, PA

    Helpful (1) (0)

  • 4/5

    Installation Time: Full Day

    June 26, 2012

    S S Flows

    The flowmaster stainless steel American thunder cat back is a very nice system . Fit and finish is very good . Took me about five hours by myself to remove and install new exhaust. This cat back definitely woke the car up but when driving it is loud inside the car when going through the gears, quites down on the highway some drone.

    Alvert00

    Year: 2000 Submodel: GT Ridley, PA, USA

    Helpful (1) (0)

  • 5/5

    Installation Time: Afternoon

    March 30, 2013

    Sounds great

    Exactly what I wanted, not too loud but wanted more deeper rumble. I got it with this catback exhaust. Installation was easy, although everything fits so tight, it takes a bit of jiggling around to get it just right. Took 2 and a half hours for one side and one hour for the other. Real pleased with the look and sound. Would recommend this product.

    NBStang

    Year: 2002 Submodel: GT Canada

    Helpful (2) (0)

  • 5/5

    Installation Time: Afternoon

    September 17, 2015

    Perfection

    After reading reviews and viewing multiple videos of systems online, I liked the sound of this catback right from the start. I didn't want a sound that would break windows, my ear drums nor that would resonate too deeply inside the car. After a very smooth installation that took about 3 1/2 hours (we took our time, cleaning, painting, greasing) I was stunned when I turned the key. The sound was perfect. A solid, clean rumble at idle. A very nice hard rumble purr upon acceleration. Heads turn constantly as I'm driving down the road. I can't say good enough things about this system.

    Tilly

    Year: 1999 Submodel: GT Rochester, NY

    Helpful (1) (0)

  • 5/5

    Installation Time: Less than 1 Hour

    October 26, 2014

    American Thunder on a 4.6L 2V

    Car sounds awesome. No too loud. With the car on a lift, got it installed in less than an hr.

    Derek281

    Year: 2004 Submodel: GT Michigan, USA

    Helpful (1) (0)

  • 5/5

    Installation Time: Less than 1 Hour

    May 16, 2014

    Classic Muscle Sound!

    Absolutely fantastic fit and finish, bolted right up and done the job in less then an hour. Love the sound, The exhaust tips fit in the bumper great!

    AMCoalK

    Year: 2003 Submodel: Mach 1 Hatboro, PA, USA

    Helpful (1) (0)

  • 5/5

    Installation Time: Full Day

    July 26, 2013

    Happy with this product

    Main problem was getting a flange nut off the old exhaust on one side due to corrosion. Flowmaster exhaust fits tight in a few spots, but otherwise installation went well. It looks good and sounds great. Not too loud... just right for me.

    MR11

    Year: 2001 Submodel: GT Illinois, USA

    Helpful (1) (0)

  • 5/5

    Installation Time: Afternoon

    March 04, 2013

    Perfect combo!

    Just got thru installing these bad boys along with an SLP catted X-pipe (AM part #23008) on my '02 GT, and I couldn't be happier. I'm 32 years old, so the days of being obnoxiously loud have come and gone. This set up is great. There's no real "drone" until you hit about 85 mph, and even then, it's not bad at all. The combo is fairly mild when you're not getting heavy on the skinny pedal... But when you do - everyone around you will know it. Great fit and finish, everything bolted up exactly like it should have. I've used cheaper products on other cars, and it's very true that you get what you pay for. I went with the stainless version simply to have all stainless from the headers all the way back. Great set up, couldn't be happier!

    Fire7428

    Year: 2002 Submodel: GT Cypress, TX

    Helpful (1) (0)

  • 4/5

    Installation Time: Afternoon

    October 25, 2012

    Great looking and sounding Catback

    I bought this catback after listening to all the audio files. It sounds great. With my Catted BBK x-pipe it is a little louder but very nice sound. Does drone a little at 2k but not as bad as my stock system did. The sound is much more mellow now but sounds like a true muscle car. The installation was very easy. I was also very surprised at the weight difference. The Flowmaster is much lighter then stock. I am not a big fan of the non rolled tips. I felt my Mach 1 looked better with rolled tips. Otherwise very happy with the product. Had great welds and sounds great. Thanks American Muscle you guys offer great products!

    Torino1985

    Year: 2003 Submodel: Mach 1 St Louis, MO, USA

    Helpful (1) (0)

  • 5/5

    Installation Time: Afternoon

    April 11, 2013

    Great exhaust but need modification for Mach1 installation

    For the most part, the installation went smoothly on my 2003 Mach1. However, we did encounter one major issue: the bolt holes in the main flange connector are too narrow to fit the stock setup. We measured the stock flange diameter (center of bolt hole to center of bolt hole) and found it was 4". The new Flowmaster flange was only 3.5" (center to center). Luckily we had a dremel tool handy to remove excess material - not fun! Flowmaster could easily solve this issue by making all flange bolt holes oval with a minimum diameter of 4". Overall, the new exhaust sounds great with an increase in overall volume of 10% - 20% and much more at higher RPMs. I also like the fact that it's not too loud at cruising speed. Definitely an improvement over the stock exhaust!

    Ronbo8

    Year: 2003 Submodel: Mach 1 Rochester, NY

    Helpful (0) (1)

  • 4/5

    Installation Time: Afternoon

    December 31, 2012

    SS flowmaster not as loud

    Very nice exhaust except I was expecting it to be louder. My Mac was louder then this exhaust. Plus side is there is no drone. I have Bbk long tubes and Bbk offroad x-pipe with this and it sounds good. Just not as loud as I wanted but still very very nice. Would recommend.

    Motomike

    Year: 2003 Submodel: GT Chicago

    Helpful (0) (1)

  • 5/5

    Installation Time: Afternoon

    August 03, 2012

    If you want more than factory rumble without going crazy, these are it

    Sounds great!! After having them on a few years, i want a lil louder, may change to high flow or no cats. Also after a few years, mufflers are rustibg, hangers rusted also, one actually fell off. Never drove it in snow, few times in the rain, think they should last longer. Factory pipes on the front of my stang are in better shape

    mustang04

    Year: 2004 Submodel: GT PA

    Helpful (0) (1)

  • 5/5

    August 09, 2016

    Sounds like it should

    This is the one thing that has been missing from such a cool looking car is the cool sound, Now it is complete. I wish I would have had it done when I bought the car but now it seems kind of like a different better car.

    Lance

    Year: 2000 Submodel: GT

    Helpful (0) (0)

  • 5/5

    July 10, 2016

    great exhaust

    I like the craftsmanship they are a good value for me they are just a little loud but a very good value

    shaker56

    Year: 2004 Submodel: GT

    Helpful (0) (0)

  • 4/5

    July 22, 2014

    Great Upgrade

    I bought this exhaust along with the pacesetter h pipe. Keeping in mind this was put on a v6 I am happy with the results. It seems to be as loud as my previous exhaust but it is not as high pitched and sounds smoother. It has only been in for a week so I am counting on some more improvements over time. Overall: The tone of the exhaust is good, nothing obnoxious. I did not install it myself but was told the fit was fine. I would recommend this product!!

    PC26

    Year: 2000 Submodel: V6

    Helpful (0) (0)

  • 5/5

    Installation Time: Afternoon

    May 14, 2014

    2000 v6

    It isn't the loudest exhaust ever. But it isn't the quietest either. The idle isn't too loud, and it sounds really nice inside the car. With an H pipe, it sounds very nice within 3000 rims

    Kev1029

    Year: 2000 Submodel: V6

    Helpful (0) (0)

  • 5/5

    Installation Time: Afternoon

    April 21, 2014

    JBA H-pipe and Flowmaster American Thunder

    I did many hours of research to figure out this was the exhaust combo I wanted to go with. I was actually nervous that it would be too loud or drone really bad. I was mostly just concerned the ride wouldn't be enjoyable anymore with the drone inside and my neighbors hating me or my passengers not being able to have a conversation or enjoy listening to music. But I decided to pull the trigger on this combo as i just loved the exhaust clips I was listening to. I installed the whole system myself in my driveway, it wasn't a difficult install. And when i fired it up afterwards and took it for a ride. . . I was EXTREMELY pleased! all expectations were blown away! The exhaust sounds AMAZING! EXACTLY what I wanted. Nice rumble, crackles on down shift, highway driving is extremely peaceful running stock 3.27 gears. I can listen to music and enjoy the ride (better than my stock exhaust actually) but everyone around me still hears it. When I put my foot to the floor it SCREAMS like a monster on the outside, but still is nice volume on the inside when getting on it. And the only drone is when the tack touches 2,000 RPM. so there is NO DRONE. My stock exhaust droned more. THIS is how a muscle car should sound. I am 110% satisfied with this setup, it is perfect. SUPER LOUD outside, like a bat out of the lower infernal regions, loud when I roll the windows down, but nice interior residence with the windows up. I HIGHLY recommend this setup!

    JoshR

    Year: 2000 Submodel: GT PA

    Helpful (0) (0)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    March 30, 2014

    Flowmaster Thunder stainless

    Better than I expected car sounds great like I have a mean engine under the hood. Wish I had done this sooner. Increased performance.

    Celery

    Year: 2003 Submodel: GT Manahawkin, Stafford Township, NJ 08050, USA

    Helpful (0) (0)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    January 12, 2014

    Good Sound

    This system had great fitment and was the easiest part of my exhaust system upgrades for the local shop to install. Hangs at a good height. Sound is great. Mine went on with a catted x-pipe and the result is pretty good. Sounds how a Mustang should sound!

    Brandon7733

    Year: 2002 Submodel: GT

    Helpful (0) (0)

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