Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004

Flowmaster: 17312
MSRP: $611.58
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Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004
Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004 Play Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004 Video 1 Play Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004 Video 2

Product Description

Flowmaster American Thunder Cat-Back Exhaust System for 1999-2004 Mustang GTs and 2003-2004 Mach 1 Mustangs.

This American Thunder exhaust system from Flowmaster has been designed with the latest exhaust technology available. Through this technology, you will experience improvements in acceleration, passing power, and fuel mileage. The key to these performance improvements is the use of 2-1/2" mandrel-bent tubing. The tubing allows for superior exhaust gas flow, while aluminized steel construction has been utilized for its corrosion-resistant qualities.

-Pair of Flowmaster Super-40 Series 2-chamber mufflers for a unique sound
-Pair of 3" stainless steel exuaust tips

Similar Mustang Parts

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Mustang Applications

This product will fit the following Ford Mustang years:

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Product Questions


how much of an increase in horsepower after installing BBK Throttle Body and Plenum ,JLT Cold Air Kit ,and Flowmaster American Thunder Exhaust on your 2002 mustang gt. I would like to increase power in my 2004 gt mustang. Thank You.

Asked by: FASTANG04
With that combo, you'll most likely want a tune as well, which will offer your the maximum increase in power. Order CJ part # XCAL4 in addition to those parts.
Answered by: CJ Pony Parts
Date published: 2015-06-10
  • 2015-11-27T08:38CST
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Product Video

Flowmaster Cat-Back Exhaust Kit American Thunder GT/Mach 1 1999-2004 Video Transcript
By Bill Tumas: So far I've added a BBK Throttle Body and Plenum as well as a JLT Cold Air Kit to our 2002 Mustang GT. These parts bumped up our horsepower and make the car a lot more fun to drive but it still does sound like a Mustang. Today, we are going to remove our factory cat-back and replace with this American Thunder Cat-Back from Flowmaster.

The basis for the American Thunder system is a super 40 muffler, a classic Mustang muffler gives the sound that everybody is familiar with. This system is a 2-1/2 inch system featuring Mandrel Bent Tail Pipes leading out to a pair of 3 inch stainless steel tips. Although, you probably don't need to hear what a stock system sounds like, we're going to fire it up anyway so we have a comparison for after. Yeah, it's just too quiet.

For this installation you’ll need a lift or a jack and jack stands, sawzall, 3/8 ratchet, 14 millimeter deep socket, 14 millimeter wrench, hammer or mallet, exhaust hanger removal tool and safety glasses. Once you get the car off the ground, the first step is going to be remove your factory exhaust system. It's going to be 1 piece all the way to the tail pipe so you have to cut behind here unless you want to remove the whole rear axle.

Now, we can remove the tail pipes from the hangers, take them off the car. Next, we'll separate the mufflers and flow tubes from our factory H-pipe. A little tap with the hammer to separate. Now, we can remove the muffler from the hangers. Now, we'll begin the Flowmaster installation by installing the tail pipes first.

Now we're ready to install the mufflers. We found by installing a bunch of these over the years cutting a couple of small slots in the muffler here will make it slide onto the tail pipe easier and give you a much better fit when you clamp it down. Now, we connect the muffler to the factory H-pipe. You can reuse your factory hardware if it is in good enough condition. In our case, we're just going to use some new nuts and bolts.

Now, we'll install the clamp between the muffler and the tail pipe. Just want to get it hand tight for now and make sure our tail pipe is where we want it before we tighten it down. It's lined up pretty good with our bumper so now we can tighten down the bracket. Now, we can repeat the process on the other side. Now let's see how it sounds with the Flowmasters on.

You got a nice deep tone you've come to expect from the Super 40 Flowmasters. The Flowmaster American Thunder gave our '02 GT a nice little growl to go along with the performance modifications we've done. Installation will take you around 2 hours. You'll be back on the road in no time.