Talk to a Mustang Expert
Mon-Thu 8:30a-11p, Fri-Sun 8:30a-9p

Free Shipping on Everything. Seriously. Details

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

100+ Reviews
Our Price


  • Item #23001
  • MPN# M31007

  • Market Price $513.95
  • You Save 4% ($21.00)
In Stock Ships same business day. Choose options to add to cart
Free Shipping on Everything
Customer Photos
  • 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 Cat-Back 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.

Fitment: 1999 2000 2001 2002 2003 2004 Details

What's in the Box
Hardware included:
  • (2) Intermediate Pipes
  • (2) Over-axle Pipes
  • (2) Resonators
  • (2) Tailpipes
  • (2) Tailpipe Tips
  • (8) Clamps
  • (2) Ball Flanges
  • Instructions
Installation Info
Tech Specs
Cat-Back 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

LOVE this catback!!!

So I just bought a 2004 Mach 1. Previous owner had a Bassani catted x-pipe with Magnaflow Street catback. Meh, it was ok, too stock sounding for my tastes. I've had SLP's before on older GT's, so I ...

Read More
Helpful (1)

Get It

This exhaust scares old people!

Helpful (42)

Overall Rating 4.9 out of 5 stars
Read All 100+ Reviews

Customer Photos (70) Submit Your Photo

View All 70 Photos

You Might Also Like

14 Questions / 7 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.


  • 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.


    Good Answer (6) (0)

Show 2 more answers Question Resolved

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.


  • 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.


    Good Answer (1) (0)

Answer This Question I need this answered (0) (0)

Will this fit a shorty off-road x pipe? Im running long tube headers and a short o/r x pipe. Will this bolt right up without modifications?


Show 2 more answers Question Resolved

More Products You Might Like

Customer Reviews (100+) Write a Review

Overall Rating 4.9

out of 5 stars

Installation Time:Afternoon

Installation Cost:$100-$250

  • Loudness / Volume 4.766667 4.8
  • Exhaust Note 4.833333 4.8
  • Fit & Finish 4.9 4.9
  • Bang For Your Buck 4.8 4.8

  • 5/5

    July 21, 2016

    LOVE this catback!!!

    So I just bought a 2004 Mach 1. Previous owner had a Bassani catted x-pipe with Magnaflow Street catback. Meh, it was ok, too stock sounding for my tastes. I've had SLP's before on older GT's, so I knew what I was getting into. But WOW, this catback paired with the Bassani x-pipe is insane! I never heard that amazing bubbly 4 valve idle on my car until I put this SLP catback on. If you've ever heard an 03-04 Cobra idle, this brings out that same sound in your 4 valve. Surprisingly there really isn't much drone considering how loud it is on the outside. But mash your right foot down and this baby SCREAMS! And of course, AmericanMuscle delivered FOR FREE within 3-4 days. Couldn't ask for a better price or better service. Thank you!


    Year: 2004 Model: Mach 1 Driving Style: Daily Driver 'Stangs I have owned: 5+

    Helpful (1) (0)

  • 5/5

    November 26, 2007

    Get It

    This exhaust scares old people!


    Helpful (42) (0)

  • 5/5

    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

    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

    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

    Installation Time: Afternoon

    October 02, 2011

    It took a little over two hours to cut off the old exhaust and install the new ones

    It's a great product that sounds really good. I thought they would be too loud but ended up being just what I been looking for. These cat backs will make heads turn. I'm sure with headers it would sound even better. I had Borla Stingers on my old mustang, they sounded good but these sounds way better!


    Year: 2004 Model: Mach 1 Driving Style: Daily Driver 'Stangs I have owned: 3 Baton Rouge, La.

    Helpful (2) (1)

  • 5/5

    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

    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

    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

    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)

Related Mustang Categories