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

100+ Reviews
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  • Item #18410
  • MPN #17312
  • Market Price $519.99
  • You Save 10% ($52.13)
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Product Videos Customer Photos
  • 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.

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.

Quality Construction. Constructed from mandrel bent 2.5" 16 gauge aluminized 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.

Fitment. This Flowmaster American Thunder 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.

Mustang 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: 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
  • Bullitt - 01
  • Mach 1 - 03, 04
  • GT - 99, 00, 01, 02, 03, 04

Fits GT, Mach 1, and Bullitt

Most Helpful Reviews View All

Overall Rating 4.7/5 Write a Review
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

Read More
Helpful (75) (8)

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

Read More
Helpful (29) (3)


Hi I’m Justin with, and I’m breaking down Flowmaster’s American thunder Catback exhaust fitting the 99-04 Mustang GT and Mach 1. A few of the big points with this catback are the 2.5” View Full Transcript

Customer Photos (21) View All

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Q & A (12 Questions, 7 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

Ramoon Year: 1999 Model: GT

Question Resolved
Good Question (7) (0)
  • 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.

    Helpful (4) (0)

    Best Answer

    00Stanger Year: 2000 Model: GT

Show 1 more answer

V6 would this bolt onto a v6

timmay Year: 2001 Model: V6

Question Resolved
Good Question (6) (2)
  • 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!

    Helpful (7) (1)

    Best Answer

    LisaS Year: 1992 Model: GT

Show 2 more answers

How would this sound on a V6? With all of the correct items in place for install how would this sound on a V6? I understand the difference but looking for any kind of insight or details as to what to expect. These items are kind of expensive so its hard just to throw a dart in the dark and hope for the best sound. Kraig

kbails84 Year: 2004 Model: V6

Question Resolved
Good Question (0) (0)
  • I've heard a set of Flowmasters on a V6 with a True-Dual, and I was surprised at how aggressive it sound. If you have the correct set up I would equate it to just above a stock 99-04 GT as far as volume and overall sound. It still won't have the rumble of a V8, but it does sounds surprisingly aggressive.

    Helpful (0) (0)

    Hawkeye4040 Year: 2003 Model: GT

    Top 500 Contributor

Show 1 more answer

Reviews (100+) Write a Review

  • 5 Stars .80 80%
  • 4 Stars .14 14%
  • 3 Stars .05 5%
  • 2 Stars 0 0%
  • 1 Stars .01 1%

out of 5 stars

100+ Customers Recommend this Product

Installation Time:Full Day

Installation Cost:$100-$250

  • Loudness / Volume: 4.267606 4.3/5
  • Exhaust Note: 4.614286 4.6/5
  • Fit & Finish: 4.422535 4.4/5
  • Bang For Your Buck: 4.577465 4.6/5
Filter By Sort By
  • 5/5

    v6 mustang

    January 10, 2010

    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) (8)

  • 5/5

    American Thunder

    March 12, 2010

    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 Model: GT

    Helpful (29) (3)

  • 5/5

    great sound

    January 22, 2010

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


    Helpful (14) (1)

  • 5/5

    True muscle car sound like no other!

    October 26, 2011

    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!

    Top 100 Contributor



    Year: 2004 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Mobile, Alabama

    Helpful (23) (6)

  • 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) (1)

  • 5/5

    more that satisfied

    January 18, 2011

    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 Model: GT Driving Style: Daily Driver

    Helpful (9) (2)

  • 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 Model: V6 Driving Style: Daily Driver

    Helpful (6) (1)

  • 5/5

    Sound Great in the V6

    December 15, 2011

    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 Model: V6 Driving Style: Daily Driver 'Stangs I have owned: 1 CT

    Helpful (4) (0)

  • 5/5

    Sounds great!!

    January 18, 2011

    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) (0)

  • 5/5

    Nice System

    December 11, 2010

    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.


    Driving Style: Daily Driver

    Helpful (4) (0)

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