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

Item 23001
SLP Loudmouth Cat-Back Exhaust (99-04 GT, Mach 1)
Review & Install - SLP Loudmouth Cat-Back Exhaust Video  
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100+ Reviews 14 Answers
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    Frequently Bought Together

    Features, Video & Details

    • 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

    Product Resources

    Customer Photos (90) Customer Reviews (100+) Questions (58) & Answers (14)

    Review & Installation Video

    Review & Install Video

    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

    MPN# M31007

    CA Residents: WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov

    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?

      Customer Photos (90) Submit Your Photo

      View All 90 Photos

        Questions & Answers (58)

        5 Top Rated Questions

        Will this bolt up to a Mac off road h pipe on my 99 gt?

        • The SLP Loudmouth Cat-Back Exhaust will not bolt directly up to the Mac off-road H-pipe. The cat-back and the h-pipe use different couplers to connect.

        Helpful (4)

        Are these legal in WA

        • This exhaust does not affect emissions so it will pass inspection and emissions, however, depending on your local land ordinances in WA this exhaust may violate a sound ordinance if they are strict in your area.

        Helpful (3)

        Will this exhaust pass the emission inspection in California?

        • The SLP Loudmouth Cat-Back Exhaust will not alter emissions and therefore will not cause your Mustang to fail emissions.

        Helpful (2)

        Does it require a tune up after. reason I ask is because I've been told because it is basically straight pipe I would need to get a tune up after or it would damage my engine from lack of back pressure

        • This will not require a tune no.

        Helpful (1)

        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.

        Helpful (1) Show 2 more answers
        10 More Questions
        do these sit lower than the stock pipes ?? in other words will I bottom out on my current set up after the install 0 answer
        With stock headers, and cats, how many decibels does it make? 0 answer
        Will this work with bbk long tube headers and bbk h-pipe? 1 answer
        Will this bolt up to a JBL off-road H pipe. 1 answer
        Will the slp loudmouth exhaust fit and sve off road x pipe 1 answer
        Will this fit on a stock H pipe 02 Mustang Gt? and does it require a tune up after. reason I ask is because I've been told because it is basically straight pipe I would need to get a tune up after or it would damage my engine from lack of back pressure. 0 answer
        Is it road legal 1 answer
        Will this hook up to a pypes off road x pipe? 1 answer
        Will this cat back exhaust bolt onto a 2003 ford mustang gt automatic transmission with a MAC off road x pipe? 1 answer
        I have a 2004 v6 and I purchased a pypes catted X-pipe, will I have any problems fitting the loudmouth 1 catback to the pypes catted X-pipe? If so what changes would I need to do 1 answer

          Customer Reviews (100+) Write a Review

          Overall Rating 4.9

          out of 5 stars

          Installation Time:Afternoon

          Installation Cost:$100-$250

          • Loudness / Volume 4.75 4.8
          • Exhaust Note 4.78744 4.8
          • Fit & Finish 4.846154 4.8
          • Bang For Your Buck 4.745193 4.7



          • 5/5

            Installation Time: Less than 1 Hour

            November 18, 2019

            Great Tone and Performance

            Great sounding System. Quick and easy install. Overall completely satisfied with the SLP’s.

            btylerb123

            Year: 1999 Submodel: Cobra

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            October 29, 2019

            She's loud

            Received all the hardware, install went pretty smooth did it solo in my garage. Sounds mean now compared to stock. Nothing looked or felt cheap and fitment was well just about perfect.

            Johns01bullitt

            Year: 2001 Submodel: Bullitt

            Helpful (0)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $100-$250

            October 16, 2019

            Old school sound

            I wanted to make my 2000 Mustang sound as much like a 70's hot rod as it could, and the SLP Loudmouth did the trick. Plus, the American Muscle videos of each exhaust system were critical to picking the right parts. It gives you that old school sound under hard acceleration, but when you're cruising at 70, I hear more road noise than exhaust. Perfect for me.

            Fauxbra

            Year: 2000 Submodel: GT

            Helpful (1)

          • 5/5

            Installation Time: Afternoon

            September 05, 2019

            SLP Loudmouth Cat-Back Exhaust

            This exhaust is awesome! Totally changed the way the car sounds and it is awesome. It is not too loud at idle, you'd never know it is a monster waiting for the gas pedal to be mashed. And when you do it sounds amazing. It fits perfectly and was easy to install. The polished tips with the SLP logo are the finishing touch to a really nice exhaust system.

            BlackMustang

            Year: 1994 Submodel: GT

            Helpful (1)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: 0-$100

            September 04, 2019

            Amazing

            These things are loud. I'm not sure if anyone is thinking these aren't but just tapping the gas peddle slightly already creates a nice deep growl. I'm in love with this system. If you're looking for deep and loud aggression. I would definitely recommend these pipes. They are no joke. Once you hit 3k RPMs is when you really open up those pipes.

            Garcia03

            Year: 2003 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            September 02, 2019

            Loud and Deep

            These sound great, I have stock headers and H-pipe. at idle its quiet but when you hit the gas it turns heads, and when you punch it all #(* breaks loose. I've always had FM with the deep rumble everyone loves, but these are a different deep sound, more modern. High quality also would def. recommend!

            ArealCustomer

            Year: 2000 Submodel: GT

            Helpful (1)

          • 5/5

            Installation Time: Shop Install

            June 11, 2019

            amazing!

            bought these from american muscle and they arrived on time and in good condition. They sound amazing and am very happy with the product! they sound way louder in person

            HenryG

            Year: 2002 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            May 14, 2019

            All time favorite

            Ive had my eye on this exhaust for a few years now - long before I even had my Mustang. Fantastic sound, great look.

            Cspencer112

            Year: 2004 Submodel: GT

            Helpful (0)

          • 4/5

            Installation Time: Full Day

            May 02, 2019

            Great sound

            The sound this gives my Mach 1 is amazing. It can be quiet at low RPMs but when you get into it, everyone turns heads. It was a bit hard to install considering it’s not a solid exhaust system and the clamps provided were difficult to tighten. All together, very great product and worth the money!

            Mach1forever

            Year: 2003 Submodel: Mach 1

            Helpful (1)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $100-$250

            April 26, 2019

            Wow!

            Just got these installed on my 03 Mach 1 and it sounds amazing! Very loud, and I love the pop/throaty sound quality. It really feels like I’m driving a different car. I previously had Magnaflow and these put’em to shame! I would recommend these SLP’s to anyone!

            Mach1Mustang03

            Year: 2003 Submodel: Mach 1

            Helpful (2)

          • 5/5

            Installation Time: Afternoon

            March 30, 2019

            Amazing sound

            I wanted something loud and smooth at the same time and was skeptical about getting this one. But man was I wrong best exhaust money can buy.

            LoganV

            Year: 2002 Submodel: GT

            Helpful (2)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: $100-$250

            March 13, 2019

            BEST EXHAUST BY FAR!!!!

            I know there are a lot of exhausts to choose from, and brand names with great reviews, however, I took a shot on this one. I was NOT disappointed!! I had flowmasters on the car previously, and the difference was night and day with the new LM1's installed. I got a slight power gain, but the sound is second to none. It is a BEAST!

            TylerG

            Year: 2004 Submodel: GT

            Helpful (2)

          • 5/5

            March 05, 2019

            SLP LM1’s

            Change the sound of my 01 GT completely, good combo with my Mac longtubes and Mac off road prochamber !

            Izzy

            Year: 2001 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Shop Install

            Installation Cost: 0-$100

            February 27, 2019

            SLP Loudmouth

            Great exhaust, sounds awesome! Even with the factory h-pipe its got some real attitude. I love it. Thanks American Muscle!

            Xkxp017

            Year: 2001 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Less than 1 Hour

            February 18, 2019

            Good

            Good sound easy to install would recommend to anyone.

            David

            Year: 2001 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Less than 1 Hour

            February 07, 2019

            Nice and loud

            Sounds amazing with the o/r x pipe nice and loud sure woke up the car and neighbors

            RigobertoC

            Year: 2003 Submodel: Mach 1

            Helpful (1)

          • 5/5

            January 28, 2019

            Slp

            You at AMerican muscle are great I will be ordering more parts

            GordonB

            Year: 2004 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            December 19, 2018

            SLP Loudmouth 1 - Everything I expected

            I wanted to upgrade the stock exhaust and after doing tons of research I decided to purchase the SLP Loudmouth 1. The sound is great. I wanted something louder but not too loud and with the stock cats, just what I wanted. Later I'll do other upgrades to make it even louder. Installing was not too difficult. I had to mess with the alignment but other than that it was pretty straight forward. Highly recommend.

            Eli

            Year: 2002 Submodel: GT

            Helpful (4)

          • 5/5

            Installation Time: Afternoon

            December 17, 2018

            Great MFing product

            This product is bangin loud and easy to install if your an experienced mechanic as myself. The best exhaust on the market, no problems putting in. Solid product.

            BrentS

            Year: 2002 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            December 04, 2018

            SlP Review

            Great sounding exhuast best one you can buy for a decent price!

            JaimeF

            Year: 2002 Submodel: GT

            Helpful (2)

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