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

19 Reviews
Our Price

$566.97

  • Item #18436
  • MPN# 817312

  • Market Price $640.68
  • You Save 12% ($73.71)
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Product Videos Customer Photos
Features
  • 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
Description
Flowmaster Sound.The Flowmaster American Thunder Catback 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 Catback 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 Catback 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
Catback 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
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 ...

Read More
Helpful (2)

5/5
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. ...

Read More
Helpful (1)

Read All 19 Reviews
Overall Rating 4.7 out of 5 stars

Videos

Hi I’m Justin with AmericanMuscle.com and I’m taking a closer look at Flowmaster’s stainless steel American Thunder Catback exhaust, fitting the 99-04 Mustang GT and Mach 1. The two View Full Transcript

Customer Photos (8) View All Photos

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5 Questions / 3 Answers

Ask a Question

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

tonyv6 Year: 2004 Model: V6

  • 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!

    Best Answer

    LisaS Year: 1992 Model: GT

    Good Answer (1) (0)

Show 1 more answer Question Resolved

will this work with the pacesetter v6 h-pipe ?

krash Year: 2004 Model: V6

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

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

Theweaverman Year: 2004 Model: GT

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

    Tracy67 Year: 2004 Model: GT Top 50 Contributor

    Good Answer (0) (0)

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

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Customer Reviews (19) Write a Review

Overall Rating 4.7

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

    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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Rochester, NY

    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 Model: Mach 1 Driving Style: Daily Driver 'Stangs I have owned: 5+ 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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 5+ 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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 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 Model: Mach 1 Driving Style: Race 'Stangs I have owned: 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 Model: Mach 1 Driving Style: Daily Driver 'Stangs I have owned: 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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 3 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 Model: GT Driving Style: Street / Strip 'Stangs I have owned: 3 PA

    Helpful (0) (1)

  • 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 Model: GT Michigan, USA

    Helpful (0) (0)

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