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

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Market Price $569.95 You Save 7% ($39.00)
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$530.95

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  • Item 23001

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    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

    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 (87) Submit Your Photo

      View All 87 Photos

        Questions & Answers (50)

        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)

        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

        Will this hook up to a pypes off road x pipe?

        Post Your Question
        10 More Questions
        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
        Do I need an adapter to bolt this up to my 3” Kooks Catted X Pipe? 1 answer
        Will any kinds of cats work on this? 1 answer
        Will this fit onto a bbk off road x pipe? 1 answer
        I have a Mach 1, and I'm wanting loud! I have had a 2v with an off road X and Borla Stingers. I was going to do the same on the Mach but wondering if the SLP's are just as loud? They are 100 less so just wondering. 1 answer
        Hi will this bolt up to a Mac shorty x pipe with Mac LT's? Thanks!! 1 answer
        Can this setup fit a pypes o/r x pipe(99-04 V6) along with MAC Ceramic Long Tube Headers(01-04 V6) and if so would you just recommend using the MAC o/r h pipe(99-04 V6) for better fitment? 1 answer
        hi I got a 2000 mustang gt and I would like to purchase kooks headers long tube 1/3/4 and the kooks catted pipe. my question is will the kooks x pipe3 inch catted work with my sap cat back? thanks 1 answer
        Will this bolt up to a bbk h pipe? 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 4.751244 4.8
          • Exhaust Note 4.781095 4.8
          • Fit & Finish 4.840796 4.8
          • Bang For Your Buck 4.746269 4.7



          • 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 (0)

          • 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 (0)

          • 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 (1)

          • 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 (0)

          • 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 (0)

          • 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 (2)

          • 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)

          • 5/5

            Installation Time: Less than 1 Hour

            November 09, 2018

            SLP LM1

            Greatest addition to my already monsterous set up. Kooks Long Tube Headers, Kooks Catted X Pipe and then the SLP LM1

            MikeM

            Year: 2002 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            November 02, 2018

            Loudmouth describes it

            Exhaust sound mean down low and rips your heart out 3k rpms. Sounds super aggressive when accelerating and is nice and mild when calming cruising down the highway. I installed with the stock catted mid pipe and the combo is perfect. You can be super loud when you want and tame when driving like grandma. I eventually plan to do the off-road x pipe also because im an obnoxious 20 year old:)

            BlakeM

            Year: 2002 Submodel: GT

            Helpful (5)

          • 5/5

            Installation Time: Afternoon

            October 25, 2018

            Loud Proud

            Great craftsmanship easy to install even with no lift. I would give 5 stars.

            John

            Year: 1999 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            October 11, 2018

            Easy

            It was easy to install. Only took a couple hours doing it by myself in the garage with hand tools. I had to use a couple extra jack stands to hold everything while I bolted everything. Overall great sound over stock.

            JeremyV

            Year: 2001 Submodel: GT

            Helpful (3)

          • 4/5

            Installation Time: Afternoon

            October 04, 2018

            Good quality, unique sound

            Lets start with fit and finish. I had to replace my pype bombs after my car rolled into a fire hydrant. The SLP fit much, much nicer and the 2 piece over the axle makes installation a breeze. The resonators (2 1/2 inch pipe ending inside larger pipe, no baffles or anything whatsoever) are polished and the tips are just sexy. Now for sound, this is definitely different from most exhausts. I also installed an offroad h pipe at the same time. If youre very gentle on the loud pedal and keep it under 2k its quiet. In fact, constant speed cruising its almost silent. But you give her the beans, and its like the devils orchestra starts playing. Sooo loud and angry, clear from 2k to redline. You better look for cops close before getting into it. And neighbors? Yeah, they now hate you for certain. And if there was a sound clip in the dictionary under "raspy", this would be it. It resonates really effin loud at certain rpms. On decel, she pops and gurgles, and at some rpms is almost as loud as when youre on it. If youre looking for the loudest, raspiest, rawest exhaust sound possible, look no further. Its not for everyone, and the second i get a noise ticket ill be switching to lm2s or installing cats. Lol.

            TrestonH

            Year: 2002 Submodel: GT

            Helpful (7)

          • 5/5

            Installation Time: Less than 1 Hour

            October 04, 2018

            SLP loudmouth

            Replaced my Borla system with the SLP and love it. Not that the Borla was a bad system by any means but the SLP has a deeper base note and more rumble/crackle which I like. Not overly loud at idle, nice purr out on the highway yet balls loud when u get on it a win win all the way around with the Loudmouth.

            MarkD

            Year: 2004 Submodel: GT

            Helpful (3)

          • 5/5

            October 01, 2018

            Loud

            Adds plenty of volume for a low price, best purchase so far!!

            BKC15

            Year: 2003 Submodel: Mach 1

            Helpful (3)

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