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

Market Price $577.99 You Save 12% ($66.81)
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  • Item 18410
  • MPN# 17312

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    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 AmericanMuscle.com, 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?

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    23 Questions / 36 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

    • 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.

      00Stanger

    Show 1 more answer Helpful (7)

    V6 would this bolt onto a v6

    timmay

    • 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!

      LisaS

    Show 2 more answers Helpful (6)

    Do I need to buy a new rear bumper??? I have a V6 it’s just a single exhaust

    GregoryB

    • The Flowmaster American Thunder Cat-Back Exhaust will require a GT bumper with the dual outlets.

      Ricky36

    Helpful (1)

    I just installed these onto my bone stock 03 gt. Now in the 2k-3k rpm range escpecially I'm noticing alot of vibration within the cabin. Is this because part of the exhaust is touching part of the car? I seem to really feel it on the accelerator and the shifter.

    StevenM

    • The Flowmaster American Thunder Cat-Back Exhaust should not be in contact with the body of the car, however, if it is, it could indeed cause a vibration. I would recommend taking a look and try to tweak the exhaust to avoid contact with the body.

      AMJEFF

    Helpful (1)

    Will this system fit a 2002 GT Convertible ?

    MikeyAero

    • This system was not designed for convertibles (interior drone), and Flowmaster has another system with Super 50's designed for GT Verts. However, it will work if you install 12" resonators between the mid-pipe and the mufflers, which I did on my 2003 GT Vert, and am very happy with the results.

      Murphstang

    Show 1 more answer Helpful (1)

    Do these mufflers have any warranty? I bought these from AM over a year ago and now there making a loud vibration noise at mid to high rpm. There's also no physical damage to mufflers.

    PaulP

    • Flowmaster does offer a 3 year warranty on all of their aluminized steel products.

      AMPaulS

    Helpful (0)

    People Who Bought This Item Also Bought

    Customer Reviews (100+) Write a Review

    Overall Rating 4.8

    out of 5 stars

    Installation Time:Full Day

    Installation Cost:$100-$250

    • Loudness / Volume 4.308411 4.3
    • Exhaust Note 4.64151 4.6
    • Fit & Finish 4.401869 4.4
    • Bang For Your Buck 4.588785 4.6



    • 5/5

      Installation Time: Afternoon

      July 11, 2018

      D.S tail pipe to short

      P.S muffler and tail pipe fit great . D.S. Was to short. Looks like it was made to weld together not clamp. I only could get tail pipe pushed in about 3/4 inch. Barely hangs in rear hanger. Also also fancy tip on ds tail pipe dented in. I pushed in ps tail pipe to match. Can’t really see tips anymore.

      JohnM

      Year: 2003 Submodel: GT

      Helpful (0)

    • 5/5

      Installation Time: Afternoon

      June 26, 2018

      Good sound!!

      If your looking for a deep muscle car sound this is for you.

      AndreaW

      Year: 2004 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      June 02, 2018

      2004 Mustang Convertible

      Very satisfied with this exhaust. Install was ok requiring some fine adjustments.

      EricW

      Year: 2004 Submodel: V6

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      May 31, 2018

      Great Sound!!!

      Flowmaster American Thunder Cat-Back exhaust sounds like America on a Mustang!!! Just replaced 18 year old Flowmaster mufflers with the complete catback. AM delivery was super fast and product was in perfect condition. Install was a breeze with exceptional fit. Performed install in garage on jack stands. A little quiet when first installed but give it a week and the sound starts to open up. Plan to add electronic cutouts for more aggressive sound with my stage 2 cams at car shows and cruises. Sound is perfect for me for daily driving as is.

      KennethM

      Year: 2000 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      March 02, 2018

      Great sound

      This exhaust definitely brought my stock gt to life with a louder deep growl that sounds like a mustang should. I am very pleased and it was very easy to install. A direct fit to the stock h pipe. A must have for any new egde mustang.

      JoeyS

      Year: 2003 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      February 10, 2018

      Flowmaster American Thunder

      This is the perfect exhaust for my 1999 Mustang GT Convertible. Now my Mustangs sounds as it should!!

      StevenS

      Year: 1999 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Less than 1 Hour

      February 07, 2018

      Love it

      The product purchase was the right fit and sound I was looking for.

      KimberlyW

      Year: 2002 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      December 11, 2017

      Mustang Sound

      Installed this behind a catless X pipe and sounds really mean. Quiet at idle but loud and nasty under full throttle. I wish the tail pipes were bigger around.

      JamieF

      Year: 2003 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      November 13, 2017

      True muscle car sound !!!

      This was a gift for my sons 16 th bday. And American muscle did a great job getting it shipped fast and arrived Perfect. Only took a little over an hour to install. Went smooth and the sound is great !!!!!! My sons excited and can’t wait to drive. Next thing is Pypes h pipe. Can’t wait

      SethM

      Year: 2004 Submodel: GT

      Helpful (2)

    • 5/5

      Installation Time: Afternoon

      November 09, 2017

      Awesome

      Easy install perfect fit. Sounds great when u get on it, no droning sound at cruise.

      MichaelS

      Year: 2004 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Less than 1 Hour

      October 13, 2017

      Cat-back

      Awesome exhaust, great fitment and amazing sound! Fits beautiful and changes the over look and sound of the car. Very impressed

      EricR

      Year: 2001 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      June 11, 2017

      Easy install, quality sound

      Installation was simple and smooth. It is not super loud but people know when you are driving by. Good deep and quality sound

      AdamS

      Year: 1999 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      May 12, 2017

      Great Exhaust

      The sound is amazing. Best purchase I have made for my car.

      DM

      Year: 2004 Submodel: GT

      Helpful (2)

    • 5/5

      Installation Time: Afternoon

      April 20, 2017

      Awesome Service and Product

      As always American Muscle was quick on the delivery and the product was great quality. So I want to say thank you, thank you for your great service and products. Ill be purchasing again very soon. Thank you.

      JamesB

      Year: 2001 Submodel: GT

      Helpful (2)

    • 5/5

      Installation Time: Less than 1 Hour

      April 04, 2017

      Good sound!

      Nice deep flowmaster sound and easy to install!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

      JordanF

      Year: 2000 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      March 23, 2017

      Easy install

      Had a friend install it for me and they could not believe how easy it was to install! Good product at a good price. Very satisfied once again. Could not believe how quickly it arrived, less than 24 hours from order to front door!

      RosemaryM

      Year: 2001 Submodel: GT

      Helpful (2)

    • 5/5

      Installation Time: Less than 1 Hour

      March 09, 2017

      Great Exhaust

      Bought this item with the BBK O/R X Pipe and goes together like a dream it sounds mean and aggressive, loud but not obnoxiously loud. Definitely let's people know you're coming I'd recommend this setup to anyone with a 99-04 GT. Very pleased with the results

      NickM

      Year: 2002 Submodel: GT

      Helpful (1)

    • 5/5

      Installation Time: Afternoon

      March 04, 2017

      Flowmasters

      Along with my BAMA tune and off road bbk x pipe they really opened the car up and sounds great. I could really feel the difference in the torque curve. My daughter runs it at the local strip and with a few extra bolt ons she just ran 8.7's in the 1/8 mile now to get it to hook up should be about flat 8's for a stock engine and tranny thanks AM.

      ShawnM

      Year: 2002 Submodel: GT

      Helpful (1)

    • 4/5

      Installation Time: Afternoon

      November 23, 2016

      With BBK long tubes and BBK off road X-pipe

      ...this system is quite aggressive. Louder at idle than expected. Wakes the neighbors in the morning. Nice and raspy above 2500 rpm. Fitment was difficult for 2 1/2". Flanges were not expanded enough for my X-pipe. Had to open up more to bolt on. If someone at Flowmaster had taken a few more seconds expanding the flanges this wouldn't have been a problem. Overall it was worth it. I'm an ASE master tech and all of my friends are very impressed with the sound.

      VortechV7

      Year: 2000 Submodel: GT

      Helpful (3)

    • 5/5

      Installation Time: Shop Install

      Installation Cost: $250-$500

      October 16, 2016

      V6 Thunder Conversion

      A lengthy engine rebuild put installing this Cat-back exhaust kit on-hold for over a year. I've had the kit installed on my car since the start of summer, and these are my findings. The sound produced by this exhaust kit is incredible! Especially for a V6 Conversion Cat-back as my install was. People that are not in the know about GT and V6 Mustangs swear that they can't tell the difference. Even though I have the Tell-tale "3.8" badge on the front quarter panels, some are so convinced that I'm running the 4.6 or 5.0 V8. I'd paired this Cat-back Exhaust kit with the BBK Ceramic OEM length Headers, Pypes Ceramic, High-flow Cats, Dual Exhaust H-style Conversion Mid-pipe and Hanger kit. So the sound that my V6 is producing may be slightly different from any other. Given the fact that the Cats had to be welded into place and wouldn't fit the factory down pipe from the Headers, I had my local shop install this kit for me. The initial start-up after the shop finished with the install, was music to my ears. I never would have guessed that a V6 could sound so amazing. The bolts had hold the system together seem to rattle themselves loose every once in a while. The tell-tale bang of the muffler hitting the black-top isn't something I, or any car owner wants to hear. But this seems to be the only negative thing I have to say about the entire system. And why I've given the Fit and Finish portion of my review 3/5 stars. Overall, if you're a V6 owner like I am, you will be very satisfied with this exhaust system, granted you take the necessary steps to avoid the bolts rattling loose like mine do.

      Aaron2741

      Year: 2001 Submodel: V6

      Helpful (2)

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