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Flowmaster American Thunder Cat-Back - Stainless Steel (87-93 LX; 1986 GT)

Market Price $627.99 You Save 13% ($82.02)
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  • Item 18456
  • MPN# 817213

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Features, Video & Details

  • Aggressive Flowmaster Sound
  • Super 44 Series Mufflers
  • 2.5" Polished Stainless Steel Tips
  • Mandrel-Bent Tubing
  • 409 Stainless Steel Construction
  • Fits 1987-1993 5.0L Lx and 1986 GT Mustangs

Review & Installation Video

Review & Install Video

Hello and welcome back to Stage 3 of AmericanMuscle’s project Foxbody, as you can see we’re currently out enjoying the fruits of our labor which took place in the first two stages, and for the first time since we started this project, I can honestly say I’m not embarrassed to be out driving it. Of course a part of that lack of embarrassment is because we haven’t pulled up to anything fast yet, there’s no doubt our GT is looking good, but what’s the point of having all those Cobra parts if we don’t have the performance to back it all up, well, welcome to stage 3 my friends, where all of that is about to change. Before we get back to the shop where we lay out our plans to increase our tire slaying abilities, let’s recap what we knocked out in stage 2. In stage 2 we completely replaced our destroyed factory convertible top, with a brand new top and rear glass, along with just about every piece of molding and weather stripping you can think of, we put the finishing touches on our convertible Cobra vision, thanks to our Cobra tail light covers and 10th anniversary Cobra style wheels, made possible through the 5 lug conversion kit we installed. Finally, we moved to the interior and made it look as good as our exterior, thanks to the freshly painted dash, new carpet, and other miscellaneous items making our GT look and feel like it was 1993 all over again. Alright, I can’t wait to get back to the shop to show you all the stuff we have in store for this stage, let’s get to it. As you can see we have some big plans for our 302, all with the goal of replicating the Cobra’s power plant, which is going to drastically improve our performance. For starters, we’re going big with a trio of parts from Ford Racing, all of which will do wonders for our 5.0. First up we’re looking at the Turbo Swirl GT40X aluminum heads from Ford Racing, these heads are a variation on the original GT40 heads found on the 93 Cobra, with a few improvements. For one they’re made out of lightweight aluminum versus the heavier cast iron and they’re designed to flow much better than the original GT40’s. To top it off, we’ve installed some Cobra valve covers. For us to see the biggest gains using these heads, our stock cam just isn’t going to cut it, so we’re going to go with a popular street cam, the Ford Racing E303. This hydraulic roller cam should really compliment those GT40’s, and is an excellent choice for any street car thanks to its low to mid range torque. Of course we’re still going to have that great lope at idle which should sound amazing by the way, but it’s not radical enough that we’re going to have to worry about stalling out at every red light. The cheery on top for our 302 has to be this Ford Racing intake manifold, which is getting nearly impossible to find anymore, this part, paired with our Ford Racing heads and cam, is going to allow our 5.0 to flow some serious air, and will complete our Cobra transformation under the hood. Alright, in order to move all that extra air out of the engine, we’re reworking out entire exhaust from the headers all the way back, in order to keep up with that Ford Racing theme we’ve got going on under the hood, we selected our ceramic shorty headers, which we’d already installed when we did all of our motor work, and are designed to work specifically with those GT40 heads. From there, we go to BBK’s off road H pipe which does feature mandrel bent 2.5” stainless steel tubing, and should bolt up to those shorty headers without issue. Finally, everything’s going to exit out of Flowmaster’s American Thunder Cat-Back exhaust, which features those iconic 44 series mufflers. This exhaust features 100% stainless steel constructions throughout, including 2.5” mandrel bent tubing, and those OE style polished tips. Alright I think it’s safe to say we’ve got the performance side of things pretty well taken care of, but we haven’t addressed the fact that this thing still handles like a boat. So we’re going to attack our suspension much like we did our engine, go big or go home. Ron and I are just finishing up installing the KONI STR shocks and struts, which are actually a killer set for the price. We’re pairing those up with the SR Performance lowering springs, which should lower our Fox about an inch and a half on all 4 corners. Finally, we have the car in the air, the wheels off, we figured this would be a great time to ditch those rusty old drum brakes, in favor of these brand new disks. To dial in our new Fox’s alignment, we’ve installed the SR Performance caster/camber plates, which should get everything back into spec without issue, and offer a little bit more adjustment in future if need be. Since our car is a convertible, we are losing some of the structural rigidity which comes along with having a steel roof, to help combat this, we’ve installed the SR Performance subframe connectors, this part along with our springs, shocks and struts, should take all the laziness out of our suspension, and get it handling like a sports car should. Alright, now everything’s pretty much buttoned up, we’re going to tie it together with one of our custom Bama tunes, and see if all this hard work has paid off in really cranking up the power. We’ve already grabbed our baseline run after stage 1 when we got the car back from painting, so I’m going to hop in, bury this thing one more time, and see what the improvements are. Alright, our baseline run with our 93 GT gave us 194 horsepower, and 266 ft/lbs of torque. With all of our stage 3 modifications, the car put down an impressive 279 horsepower, and 317 ft/lbs of torque, making for a solid gain of 85 horsepower over our baseline numbers. The car did even better throughout the power band, picking up as much as 103 horsepower, and 107 ft/lbs of torque, throughout the curve. With the power finally there to back up our Cobra appearance, I think it’s time for one more cruise to see how our Fox does with all its modifications. Alright, stage 3, performance, check. The car's breathing better, the tune brought it all together, and as a result, this thing has some serious balls. Here we are, we’re in the back roads, moving along at a good clip, I’d saying the car is doing quite well, it’s pretty confident, I feel confident driving it, I don’t feel like I’m going to fly off the road, which I couldn’t have said before we did all this work. The car feels good, sounds awesome, and it’s just a whole hell of a lot more fun to drive. I know some people might question this build, you know, why a convertible, why a Fox body, well, because we wanted to, I mean that’s what car building is all about, it’s doing what you want. In this case, we’ve never seen Cobra convertible Fox bodies, so we wanted to build one, and I think we did a hell of a job. So is this the last you’ve seen of this car? I don’t know, maybe, maybe not, but in the meantime, thanks for watching stage 3 of AmericanMuscle’s project Fox body.

Flowmaster Sound. Give your Mustang that unmistakeable Flowmaster sound with a nice power boost by installing a American Thunder catback Exhaust system. Featuring mandrel bent tubing this Flowmaster system will improve exhaust flow for an increase in power, and the included Super 44 Series Mufflers will improve your exhausts sound for a deeper throatier muscle car exhaust note.

Stainless Steel Construction. Constructed from mandrel bent 2.5" 409 stainless steel tubing for it's corrosion resistant properties the Flowmaster American Thunder catback features Super 44 Series chambered mufflers with 25" Long by 2.5" diameter OEM style polished stainless steel tips for muscle car looks and sound.

Application. This Flowmaster American Thunder stainless steel Cat-Back exhaust system is designed to fit the 1987-1993 LX and the 1986 GT Mustangs for both great looks and great sound.

Fitment: 1986 1987 1988 1989 1990 1991 1992 1993 Details

What's in the Box
  • (2) Muffler assemblies
  • (2) Over axle pipes
  • (2) Exhaust Tips
  • (2) Clamps
Installation Info
Tech Specs
Cat-Back Exhaust Specifications
Piping Material: 409 Stainless Steel Tip Material : Polished Stainless Steel
Piping Size: 2.5" Tip Size: 25"L x 2.5" diameter
Muffler Type: Chambered Fitment: 87-93 LX and 86 GT Mustangs
Will it fit my Mustang?
  • Foxbody - 86, 87, 88, 89, 90, 91, 92, 93

Fits 1986 GT and 1987-1993 LX Mustangs

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Most Helpful Reviews

Great product

Great product, however the hole pattern was off by an 1/8 of an inch and had to be modified, which took about 3hrs, other than that I love them!!!

Helpful (1)

Best sounding exaust real nice sound!!

The quality of the flow master system is flawless. it fit perfectly .and the exaust note is loud .But it the sound you cant beat it .I have a built 331 ford stroker in my 1990 mustang and now you really ...

Read More
Helpful (1)

Overall Rating 4.9 out of 5 stars
Read All 7 Reviews

Customer Photos (2) Submit Your Photo

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4 Questions / 3 Answers

Ask a Question

Will this fit on to a bbk x mid pipe ( Item 56136 MPN# 1660 ) and although I have a '83 GT will this fit because I can't find any full length exhaust. I will also be buying the bbk long tube headers ( Item 386982 MPN# 15690 ) and would this set up be a right none leaking exhaust for my 1983 5.0 manual hatchback.


I have BBK shorty headers on my '86 Fox. Will these fit?


  • The Flowmaster American Thunder Cat-Back - Stainless Steel should bolt up to your car with short headers with no issues!


Helpful (0)

The tips do they have the Flowmaster name of n them


  • The Flowmaster American Thunder Cat-Back - Stainless Steel (87-93 LX; 86 GT) do not have the Flowmaster wordmark on the tips.


Helpful (0)

Does this fit the 1993 SVT Cobra? I've been told that this fits the 93 cobra, but you need to lengthen the hangers. Is this difficult? What does it entail?


  • The Flowmaster American Thunder Cat-Back - Stainless Steel (87-93 LX; 86 GT) will fit a 93 Cobra as the size of the tubing is the same as the LX & GT models. As for the hangers, as long as the existing exhaust hanger base is still in good shape the hangers attached to the Flowmaster American Thunder Cat-Back - Stainless Steel (87-93 LX; 86 GT) should be the correct size for it to comply with the base.


Helpful (0)

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Customer Reviews (7) Write a Review

Overall Rating 4.9

out of 5 stars

Installation Time:Afternoon

  • Loudness / Volume 4.857143 4.9
  • Exhaust Note 5 5
  • Fit & Finish 4.428571 4.4
  • Bang For Your Buck 4.857143 4.9

  • 5/5

    Installation Time: Afternoon

    July 17, 2014

    Great product

    Great product, however the hole pattern was off by an 1/8 of an inch and had to be modified, which took about 3hrs, other than that I love them!!!


    Year: 1987 Submodel: Other Denver, CO, USA

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    July 01, 2014

    Best sounding exaust real nice sound!!

    The quality of the flow master system is flawless. it fit perfectly .and the exaust note is loud .But it the sound you cant beat it .I have a built 331 ford stroker in my 1990 mustang and now you really can hear the power when you get on the throttle.


    Year: 1990 Submodel: Cobra NEWJERSEY

    Helpful (1)

  • 4/5

    Installation Time: Afternoon

    October 18, 2013

    This is a high quality exhaust system.

    This is a great product but not something a novice can install alone. It is a high quality product with a great finish on the polished stainless steel pipes. The installation is not very forgiving. It required heating and shaping the connections to get them together and a precise mounting to get both tailpipes to line up exactly the same. Don't get me wrong, now that they are installed, I love this exhaust system. The sound is awesome.


    Year: 1992 Submodel: Other Hamburg, NY 14075, USA

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    July 24, 2013

    86-93 Flowmaster American Thunder Catback 409SS

    Well built and an easy install. Shipped safely to ensure tailpipes arrive without dings/damage. Classic Foxbody sound with an offroad H-pipe. Maybe no better sound in the history of the automobile than this combination.


    Year: 1982 Submodel: Other

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    September 18, 2017

    Stainless Steel American Thunder System

    We'll built, easy to install and the thunderous sound is awesome!!


    Year: 1991 Submodel: LX

    Helpful (0)

  • 5/5

    Installation Time: Less than 1 Hour

    July 01, 2017

    Great system

    Is there any other exhaust for a foxbody? I think not. Excellent product and fast shipping


    Year: 1989 Submodel: LX

    Helpful (0)

  • 5/5

    Installation Time: Afternoon

    January 11, 2015

    No better product for the money.

    I honestly couldn't be more happy with this purchase. Shipping was fast and easy, everything was well packed and not a single scratch on any of the finished tips! Easy installation that took about 2 hours, with mostly adjustments to get the tips lined up perfect with no sag. Highly recommended product. And would recommend the all 409 stainless exhaust, for the money you couldn't ask for a better exhaust system for your car.


    Year: 1990 Submodel: GT Leesburg, FL, USA

    Helpful (0)

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