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SLP Loudmouth Catback Exhaust (99-04 GT, Mach 1)

100+ Reviews
Our Price


  • Item #23001
  • MPN# M31007

  • Market Price $524.99
  • You Save 6% ($32.04)
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  • Rich, throaty exhaust tone
  • Loudmouth "shotgun" race resonators included
  • Versatile modular design
  • 2.5" 409 stainless steel tubing
  • 3.5" polished 304 stainless steel tips
  • Fits 1999-2004 GT, Bullitt, & Mach 1 Mustangs
More Power and Sound.   This SLP system includes SLP's infamous Loudmouth "shotgun" race resonators that offer virtually zero flow restriction to free up more power and to produce the most aggressive sound possible.

Modular Design.   SLP's unique modular design allows you to quickly and easily switch out the mufflers or resonators to suit your driving needs. Along with the included resonators, the Loud Mouth system is compatible with all SLP mufflers and resonators including the bullet-type Loud Mouth II and the traditional-style PowerFlo Muffler.

Superior SLP Construction.   This SLP Catback system is made from mandrel bent 2.5" 409 stainless steel tubing for for its excellent non-restrictive flow characteristics and long life. The system ends with a brightly polished 304 stainless steel 3.5" tips, that are electro-marked with the distinctive SLP logo, giving a great finishing touch and a show quality look.

Application.   Designed to be a direct bolt on, this SLP Loudmouth catback will bolt straight up to the factory Mid-Pipe without any extra modifications required on the 1999-2004 GT, 2001 Bullitt, or 2003-2004 Mach 1 Mustang to give it a rich, throaty sound.

Mustang Fitment: 1999 2000 2001 2002 2003 2004 Details

What's in the Box
Hardware included:
  • (10) Ten Clamps
Installation Info
Tech Specs
Catback Exhaust Specifications
Piping Material: 409 Stainless Steel Tip Material : Polished 304 Stainless Steel
Piping Size: 2.5" Tip Size: 3.5"
Muffler Type: Straight-through Fitment: 1999-2004 GT / Mach 1 / Bullitt Mustangs
Will it fit my Mustang?
  • Bullitt - 01
  • Mach 1 - 03, 04
  • GT - 99, 00, 01, 02, 03, 04

Fits GT, Mach 1, and Bullitt

Most Helpful Reviews Read All Reviews

Overall Rating 4.9/5 Write a Review
Get It

This exhaust scares old people!

Helpful (42) (0)

Just Perfect

Dont listen to anyone who tells you these are too loud. They are not.They are perfect. They do \'shout\' dont get me wrong and people will move out of your way (i love when that happens to me :-) but they

Read More
Helpful (34) (2)

Customer Photos (65) View All Customer Photos

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Q & A (14 Questions, 5 Answers) Ask a Question

Will this sound ricey with my v6 mustang? Ill be using an off road x pipe, i also have a cai and 65mm throttly body installed.

Larryde Year: 2002 Model: V6

Question Resolved
Good Question (1) (0)
  • I assume you have a dual exhaust system on your V6 or are building one. Part of what you can do to help get the growl is use an H-Pipe vs an X-Pipe. It changes the harmonics up. Check out the clip and keep in mind that this is a stock GT exhaust with Factory manifold and factory h-pipe. Find an exhaust with a sound like what you're after. The SLP Loudmouth sires is just that, Loud. If you want more of a rumble, you might try the magnaflows.

    Helpful (5) (0)

    Best Answer

    SteelWolf Year: 2004 Model: GT

    Top 250 Contributor

Show 2 more answers

Will this fit on a 99 v6 base model? I was wondering if this would fit on a 1999 3.8l v6 base model, everything is stock on it.

SeanH Year: 1999 Model: V6

Question Resolved
Good Question (0) (0)
  • No, it will not fit due to the stock mid pipe converging to a "Y." Upgrade your mid pipe to an X or H and this will bolt up.

    Helpful (1) (0)

    2003 Year: 2003 Model: V6

Will the Pypes Off-Road X-pipe strap up to this? I have a 2003 V6 with a MAC dual conversion kit on it. I have recently purchased the o/r x-pipe and am looking for a louder setup-the SLP Loudmouths. Will those two go hand-in-hand fitment wise? Or will I need to additoinally purchase some aftermarket mandrel bent tubing for any sizing issues?

2003 Year: 2003 Model: V6

Question Resolved
Good Question (0) (0)
  • If you ordered the Pypes Off-Road X-pipe designed for the 99-04 V6 Mustangs, that x-pipe and this SLP Catback will bolt up to one another with no problems and no additional tubing to be purchased. To ensure you are coupling the correct pipes, I've attached the appropriate x-pipe below so you can double check. If you have any additional questions, please give us a call!

    Helpful (0) (0)

    LisaS Year: 1992 Model: GT

Reviews (100+) Write a Review

  • 5 Stars .94 95%
  • 4 Stars .05 5%
  • 3 Stars .00 0%
  • 2 Stars .00 0%
  • 1 Stars 0 0%

out of 5 stars

100+ Customers Recommend this Product

Installation Time:Full Day

Installation Cost:$100-$250

  • Loudness / Volume: 4.777778 4.8/5
  • Exhaust Note: 4.809524 4.8/5
  • Fit & Finish: 4.920635 4.9/5
  • Bang For Your Buck: 4.746032 4.7/5
Filter By Sort By
  • 5/5 Yes, I recommend this product

    November 26, 2007

    Get It

    This exhaust scares old people!


    Helpful (42) (0)

  • 5/5 Yes, I recommend this product

    April 13, 2009

    Just Perfect

    Dont listen to anyone who tells you these are too loud. They are not.They are perfect. They do \'shout\' dont get me wrong and people will move out of your way (i love when that happens to me :-) but they are not obnoxious, I contemplated for the longest time on which catbacks to install on my 04 V8 GT. Got them put a week ago went down to the NJ shore this weekend...The drive was brilliant... Definitely recommended. PS they might be \'Too loud\' if you throw on and O/R pipe or something but i have the stock mid pipes and they are great. if you like something with a bite,these are it and AM ships right on time every time. I do all my \'car\' shopping out here. Kudos to AM and to my cat backs. cheers


    Year: 2004 Model: GT

    Helpful (34) (2)

  • 5/5 Yes, I recommend this product

    January 31, 2010

    This exhuast = BA

    This exhaust was very easy to assemble, and very easy to line up. the tubing is already notched for easy clamping. Plus, the sound is very nice and loud. It gives my car a very muscular sound. So in all that is why i say this exhaust = Bad A**


    Helpful (19) (0)

  • 5/5 Yes, I recommend this product

    August 13, 2009

    They Bark!

    I really like this exhaust. I also added a BBK ceramic coated long tube header and BBK shorty H-pipes with the cats and this system is the perfect addition. When you don't get on it, it's a "medium" mellow tone. Not too loud, but loud enough. When you get on it, it flat out barks! I mean it's loud! I love it!! It reminds me of my GTO with headers and glass packs from years gone by. I do recommend this combination, if you're into the sounds of the "old days".


    Helpful (17) (1)

  • 5/5 Yes, I recommend this product

    July 22, 2008

    hear me roar

    They are bad ass. I was pulled over by the Ohio state troopers just to tell me how bad ass my 2004 mustang gt sounds with the SLP loudmouth exhaust installed. It was and is an awesome system.

    p simms

    Year: 2004 Model: GT

    Helpful (7) (0)

  • 5/5 Yes, I recommend this product

    August 16, 2010

    03 stang

    sounds nasty, but in a good way really you will love this cat back. took a wile to take off the stock exhaust, nuthing a hak saw cant take care of. the loud mouth went on very easy but i have a friend that has lift. good mean sound when you start it turns a lot of heads im the parkin lots. its not loud unless you want it to be cops dont even look at you. but when munch on that gas you will get chills. the only problem i have with it is when i drive down the interstate at about 2000 it has a lot of exhaust sound in the cab sounds good at first but gets a little old but all in all i love it. thanks AM


    Year: 2003

    Helpful (10) (3)

  • 5/5 Yes, I recommend this product

    December 21, 2010


    Catback with catted x-pipes sounds awesome. Quiet when under 2k rpm but after it roars!!! Travel down highway and no annoying sounds. Hear radio just fine. Thank you A&M for good product to reach my door as promised.


    Driving Style: Daily Driver

    Helpful (5) (1)

  • 5/5 Yes, I recommend this product

    June 13, 2009

    2004 V6

    I recently just put this cat back on my car along with a pypes catted X and BBK shorty headers and its louder than any other modded V6 I\'ve ever heard. No joke when i rev this B*TCH up she screams her ass off. GREAT PRODUCT THANKS AM!


    Year: 2004 Model: V6

    Helpful (4) (0)

  • 5/5 Yes, I recommend this product

    April 07, 2008

    2003 3.8L V6

    Exhaust was easy to install once I got my v6-v8 adapter (H-pipe) welded on. I was a little unsure about the sound I was going to get...with my car being a v6, and with my friend and his MAC y pipe exhaust sounding nice, I didn\'t know what to expect. When the exhaust was done, his jaw was on the ground and he wanted my same SLP loudmouth setup.


    Year: 2003 Model: V6

    Helpful (4) (0)

  • 5/5 Yes, I recommend this product

    December 11, 2010

    slp loudmouth 1

    this catback and an o/r xpipe is perfect if you want the attention! iam not goin to lie but you can hear my o3 Gt from blocks away! slp is great! AM is great

    jesus sanchez

    Driving Style: Show

    Helpful (3) (0)

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