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1999-04 Ford Mustang Flowmaster American Thunder Cat Back Exhaust System GT-Mach 1 - New Edge by Flowmaster

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Mustang Flowmaster American Thunder Cat Back Exhaust System (99-04)
  • Flowmaster Mustang American Thunder Cat Back Exhaust System (99-04) GT-Mach 1
  • Flowmaster Mustang American Thunder Cat Back Exhaust System (99-04) GT-Mach 1
  • Flowmaster Mustang American Thunder Cat Back Exhaust System (99-04) GT-Mach 1
  • Flowmaster Mustang American Thunder Cat Back Exhaust System (99-04) GT-Mach 1

Flowmaster American Thunder Exhaust Systems add a signature growl that's best described as the "Flowmaster Sound" - A muscular, throaty rumble that announces your engine's presence. Flowmaster is the true tone of classic American muscle and performance.

Item# FLO-17312

Your Price: $419.16

Market Price:$505.98
You Save 20.71 % ($86.82)

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  • Gives Your Mustang That Signature Sound
  • Increased Performance
  • Improves Exhaust Tone


  • Fully Welded Construction
  • H-Chamber Design
  • Aluminized Steel
  • Black Painted Mufflers
  • Made In The USA
  • Fits 99-04 GT And 03-04 MACH 1 Will Not Fit Vehicles Equipped With IRS
  • 3 Year Warranty

What's in the Box

  • (2) Muffler Assemblies With Flow Tubes
  • (2) Tailpipes with Stainless Steel Tips
  • (2) Exhaust Clamps
  • Install Instructions
  • Flowmaster Stickers
  • Warranty Card

Made in the USA

Product Description

For the person who is looking for a complete cat-back dual exhaust system with an aggressive tone for their 1999-04 Mustang GT, this is the kit to have. With easy fit in mind, these American Thunder systems from Flowmaster are mandrel bent for maximum performance and include specially selected mufflers. American Thunder systems deliver a moderate to aggressive interior and exterior tone and are suited to the enthusiast who wants their performance to be heard. Like all Flowmaster systems, the American Thunder benefits include improved throttle response, power and mileage. Designed for an easy fit, these Mustang exhaust systems include all necessary parts and hardware for easy installation.

Since Flowmaster mufflers use sound energy cancellation technology, you don't have to worry about "packing material" deteriorating and getting louder after as little as a few months. The interior case volume of the inside of a Flowmaster muffler is far superior to that of a "straight-pipe" or "straight-through" muffler design. Imagine filling a "straight-pipe" or "straight-through" muffler with water vs. filling a Flowmaster muffler with water. Which one do think would hold substantially more volume? The deflector in a Flowmaster muffler acts as a one way check valve eliminating reversion back to the engine and creates a low pressure area to help scavenge the exhaust. Flowmasters unique style of H-Chamber designs help control interior resonance inside the cab area of your vehicles. "Straight-through" muffler designs cannot. Flowmasters use fully welded construction for added strength and durability to last even when installed on high horsepower engines.

Flowmaster mufflers are made in the U.S.A.

- Fits 99-04 GT, 2001 Bullitt, and 03-04 Mach 1, will not fit Mustang Cobra equipped with IRS.
- 2.5" Inlet / 3" Tip
- Super 40 Series Mufflers
- Aluminized Steel Construction
- Stainless Steel Tips

Product Videos

Check out our YouTube channel for even more tech tips, installation videos, how-tos, and more. The best place to go for anything Mustang related!

Community Q&A

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Customer Reviews

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3 of 3 REVIEWS
3 of 3 REVIEWS

  Fast delivery
By on 4/7/2014
Great fit

Yes, I would recommend this item to a friend!

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  sounds great
By on 8/24/2014
Thanks LMR. You provide great service. I'm not a mechanic but with a jack and jack stands I was able to install the flow master cat back in four in a half hrs. It really sounds great on my 01 GT convertible. Not too loud and in my opinion just right. Directions from flow master are "just OK" but can be figured out with common sense. Just a heads up, you will need a 13 and 14mm deep socket to complete the install. (Which I didn't know) I'm very happy with the whole buying experience and the end result.

Yes, I would recommend this item to a friend!

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  Fast easy
By on 5/19/2014
Ordered a couple weeks ago received tracking info ASAP got eaxactly what I ordered could not be happier
Not too loud can come home and you won't here me coming unless I want you too (still pleanty loud when you step on it)

Yes, I would recommend this item to a friend!

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Vehicle Applications

Ford Mustang - 1999 (99) - 2000 (00) - 2001 (01) - 2002 (02) - 2003 (03) - 2004 (04)

About This Brand

Flowmaster - The Exhaust Technology Company
Flowmaster operates the only exhaust Research & Design facilities of its kind in the world, centered around the SuperFlow SF-7100 engine dynamometer complete with E.C.A. (engine cycle analysis) equipment and also SuperFlow chassis dyno's.

Through use of these dyno's, Flowmaster's engineering staff can track the complete engine cycle in millionths of a second and can obtain exact technical data of each degree of cam rotation, from induction to the tip of the exhaust system, while also showing the power numbers that really matter, the power numbers "to the ground."

Flowmaster also utilizes Spectrum Analyzers to fine "tune" the sound of each of the eleven different series of mufflers that Flowmaster currently offers, both for peak performance and just the right sound levels and tones. Flowmaster's dedication to quality is what makes them the exhaust industry leader for Latemodel Mustangs and SVT Lightnings!

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