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

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    Features, Video & Details

    • Rich, Throaty Exhaust Tone
    • Loudmouth II "Bullet-Type" Race Mufflers 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

    Hey, guys, Adam here with americanmuscle.com. Today, we're taking a closer look at listening to and installing the SLP Loudmouth II Catback exhaust available for the '99 to '04 GT and Mach 1 Mustangs. Now, if you're the owner of that 4.6 New Edge, you might be in the market for a new catback to not only give you a more aggressive tone but also a better appearance at the rear end and, overall, just a better sounding Mustang. Now, as you heard from our sound clips, I'm gonna give this one three-out-of-five on our loudness meter. It's definitely not the loudest of the loud, but it is absolutely aftermarket. It has a rich, deep, throaty aggression to it, and it's not too overwhelming. Now, inside the cabin, not a whole lot of drone, if any at all. At fifth gear on the highway, there was a little bit of drone, but it was pretty tamed. Nothing too overwhelming inside the cabin. Now, other than that, this thing is going to be pretty loud at wide-open throttle, and on deceleration, you can expect some backfire, which, personally, I really like. Now, the tips are three-and-a-half inch 304 stainless steel, which is a nice polished finish. Looks a little bit better than the factory but still very similar in design, only these are gonna have the SLP logo almost laser etched on the top end, which I personally think looks really good as well. Now, the rest of the system is completely modular, which is something to keep in mind. So if you pick up this system, and later on down the road maybe you want to change out those bullet-style mufflers, the modular system will allow you to do so. So what that basically means is all you have to do is unbolt those bullet-style mufflers or resonators from SLP and swap them out with another SLP product. Or if you have something of the same size that would fit, you can do so. The modular system allows you to change it up whenever you want. This one comes in right around the $500 mark, and it's gonna get two-out-of-three wrenches on our difficulty meter. Now, guys, there is a very small amount of cutting involved, very small amount of cutting. Some guys might be lucky enough to be able to slide this out without having to cut. But right behind your factory tips, you may need to cut that pipe in half. That's going to make it a lot easier for you to slide the over axle pipe over the axle to get your factory exhaust uninstalled. Other than that, very simple system, bolt-on, very simple hand tools required. I'm gonna take you through every step of the process. Takes you about two hours from start to finish. What do you say we get started? Tools used in this install include an impact gun, 14 and 15-millimeter deep sockets. Hanger removal tool is definitely recommended as well as PB B'laster or WD-40, and we used a Sawzall for cutting. This is a much bigger Sawzall than you need, but a cutting tool of your choice and a metal cutting blade. All right, guys, the first step of the uninstall here to get your factory catback out of the way is to grab a 14-millimeter deep socket. We're gonna remove the four bolts holding on your factory catback to your mid-pipe. As you can see there's two flanges, one on each pipe here, both of which has two bolts. I'd recommend grabbing some PB B'laster before you get started, hit those bolts with a little PB. These New Edges can be pretty old and sometimes pretty rusted and corroded, so having PB B'laster definitely makes life a little easier. We've already taken care of that as you can see, so let's loosen them up and get them off. All right, next up we're gonna grab a hanger removal tool and pop these hangers out of their isolators. Now, on each side there's two of them, one on the pipe and then one over here on the muffler itself. So, grab a hanger tool and pop them off. All right, do the same thing on the other side. All right, guys, at this point, I want to stop down and take a quick second to explain the cutting situation. Now, in some cases, guys, you may not need to cut if you're able to slide your over axle pipe out of the hangers by the tips all in one piece. But depending on your situation, you may need to cut right here where you see this clamp. Now, we've already taken care of the cutting in the past for previous videos so we have a clamp right here, but I still want to show you guys what that cutting is like. We still have footage of that, so I'm gonna show you guys some of that footage of us cutting this factory exhaust off. So, your Sawzall or something similar will do the trick. If you're not comfortable with that, of course, taking it to a professional is the way to go. But if you have the right tools, you can definitely get it done. I'm gonna remove this clamp, but let's see how that cutting is taken care of. All right, so once that's disconnected and cut, you can see the over axle pipe with the muffler hangs down on the axle itself. You can just pull it out in one piece. All right, guys, we finally got our factory catback off of our '99 GT sitting on the ground next to our SLP Loudmouth II. I want to take you through some of the similarities but mainly the big differences between the two kits, and there are quite a few to mention. Your factory catback here, as you can see, over the years gets pretty rusted, corroded. Doesn't look very good. Some of the hangers might be looking a little bad as well as the flange, so it's good to update all the systems with something of a better quality. The SLP Loudmouth here is using two-and-a-half inch 409 stainless steel mandrel bent tubing, mandrel bent meaning it is going to be a lot smoother, better for airflow, less restrictive than your factory catback that can have some kinks and some of those bends. 409 is also a better quality material than your factory catback, so it's not going to end up looking like this after a few years. It'll definitely hold up a lot longer. Now, the rest of your system here includes bullet-style mufflers, which are the small muffler almost resonators that you see, which is a huge difference from the factory option. That's really what's gonna convert this to almost like a straight-pipe-style design. There's not a whole lot of baffling involved here. You can pretty much see right through them, which is creating that sound you heard. It's creating that noise, the tone, little bit of drone, the raspiness of this catback. It's also going to create a little bit of that backfire. Now, toward the end of the system, you can see that it has a similar tip style to the factory, just a little bit more polished up. Those are three-and-a-half inch polished 304 stainless tips. 304 is the highest quality material on the market, so the tips are gonna hold up a lot longer, which is good because that's really what you're seeing from the exit style of this catback. So the dual exhaust here, the tips coming out the rear are gonna hold up a little bit longer. And, that's gonna be a good thing because they're good to be polished up and have that show car finish. Now, they do have the SLP name embedded in the materials on top. I like when brands put their logo on that tip so you can really represent. Now, we're going to show you guys how to install this. You're gonna use the same isolators from the factory. If your isolators are looking pretty beat up, now is a good time to swap them out. You can pick those up at your local auto parts store. Our's looking pretty good, so we're still going to reuse those. All clamps are included in the kit. You're also going to use a new flange for your connection to your mid pipe, in this case is our H-pipe. So we'll grab that and start there at the flange. All right, grab one of the flanges included in the kit as well as your exhaust pipe that will connect to the flange. Now, there's two different sizes. The smaller one is going to go on your driver side, the longer pipe is going to go on your passenger side. So we're going to show you guys how it works here on our driver side, so we're gonna slide the flange on the exit down to the stopper. Now, that will connect to your factory studs. So, slide those over, and align the studs. They're gonna seat properly inside of each other, then you're gonna grab your factory nuts, and thread those on to the studs just like that. Now, when we tighten these down, you want to leave a little bit of room to make adjustments so we can angle it properly. But, for now, we're gonna have this angled toward the outside of the vehicle. All right, from here, grab your 14 socket, and you can tighten this guy down. But, again, just nice and snug, not too tight. Leave room for adjustment. All right. Now, you can do the same thing on the other side. From here, you can take your SLP muffler, and you're gonna slide that over the exit with one of the clamps installed over the inlet. Once you have that taken care of, grab a 15 socket and tighten down that clamp. All right, do the same thing for both sides. All right, next up is our over axle pipe. Now, you'll know which side's which depending on the hangers. The taller hanger is gonna be on the left side going up to that taller or higher up isolator. So, line that guy up, slide it over the axle, connect it to your muffler with a clamp installed on that inlet. And, before we tighten anything down, slide these hangers into those isolators just like that, and the same thing on the top guy. All right, once that guys in that isolator, you can slide that guy in and then reconnect your pipe. From there, tighten down your clamp. All right, we can keep going with that over axle pipe with the next one for our driver side. Now, that, again, is very specific. You'll figure that one out because it'll go straight toward the isolator where your tip will go. You want to make sure you're using the pipe that makes the tip line up properly. Grab your 15 socket with that clamp and tighten it down. All right, finally, the tip on your driver side. You want to make sure you're sliding it in that isolator first, slide it back as far as you can, and then connect it to your pipe. Perfect. All right, from there, make sure it's aligned, tighten down your clamp. Now, you can just repeat the exact same process on the other side. At this point, make any adjustments that you need to to get everything lined up properly, tighten down all your clamps, and you're good to go. Well, guys, that's gonna wrap up my review and install for the SLP Loudmouth II Catback for the '99 to '04 GT and Mach 1. If you want to pick this one up, you can do so right here at americanmuscle.com.

    More Power and Sound. This SLP system includes SLP's famous Loudmouth II "Bullet Style" race mufflers for minimal restriction, increased horsepower and an aggressive tone, that are only second to the Loudmouth "shotgun" race resonators for sound.

    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 bullet mufflers, the Loud Mouth II system is compatible with all SLP mufflers and resonators including the shotgun style Loud Mouth Resonators 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 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 II 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# M31007A

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

    What's in the Box
    Hardware included:
    • (8) exhaust system band clamps
    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 (42) Submit Your Photo

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        Questions & Answers (11)

        5 Top Rated Questions

        Are these good with stock mh pipe

        • Yes, this cat-back will bolt right up to the factory mid-pipe.

        Helpful (0)

        I have a pypes catted x pipe will this bolt right up or no?

        • This would bolt up to the Pypes catted X pipe as both have 2.5" collectors. 

        Helpful (0)

        What makes this model different the the first version? Thanks.

        • The difference between this exhaust and the first version would be the muffler style. This exhaust would have a bullet style muffler rather than the shotgun resonators that the first loudmouth exhaust has. This exhaust would be louder as well as have a deeper throatier tone to it when compared to the first loudmouth exhaust.

        Helpful (0)

        Will this exhaust fit if have the cats taken off?

        • The SLP Loudmouth II Cat-Back Exhaust will work with an off road mid-pipe. If you have any other questions or concerns feel free to call or chat in.

        Helpful (0)

        Does anyone know if these pass smog in California w/ catted x pipe?

        • The SLP Loudmouth II Cat-Back Exhaust will pass CARB however, the Catted X-pipe will not pass CARB.

        Helpful (0)
        Post Your Question
        6 More Questions
        I have pypes violator catback how does this compare in tone, aggression and loudness? 1 answer
        Would this system bolt up to bbk headers and xpipe? 1 answer
        will the lm2 for 99 gt fit my 84 gt can it be made to fit 1 answer
        So I like the outside sound of these but I was wondering what's the drone like on the freeway? My friend has the borla ataks w/catted Xpipe and bbk short headers. They sound really nice but after we put on the header and Xpipe they started to drone so bad. I will be daily driving this car and would like a nice sound with as little drone as possible. 1 answer
        any body have these with o/r h pipe ? i have lm1s with a mac o/r h pipe and was lookin for a better sound not just loud . how do the lm2s sound ? or whats a better resonator? i like it loud tho 3 answers
        Can this product fit under a v6? I have looked at the dual conversion kits for v6 on here and they aren't true dual conversions as far as I could tell. They use a y pipe.. 3 answers

          Customer Reviews (90) Write a Review

          Overall Rating 4.9

          out of 5 stars

          Installation Time:Afternoon

          Installation Cost:$100-$250

          • Loudness / Volume 4.291667 4.3
          • Exhaust Note 4.895833 4.9
          • Fit & Finish 4.916667 4.9
          • Bang For Your Buck 4.729167 4.7



          • 5/5

            Installation Time: Afternoon

            May 30, 2019

            SLP Loudmouth II

            Exeeded expectations. The quality is excellent. The install was super easy. I paired this with an off-road h-pipe and haven’t turned my radio on once since the install (three weeks ago). The exhaust note is clean, deep, and LOUD! Very minimal drone inside the cabin but turns heads everywhere.

            Laith

            Year: 2003 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            May 03, 2019

            couldn't be happier

            Installed on my 2003 Gt with the BBK 1-5/8 IN. Long Tube Headers and BBK Competition Series off road x-pipe and it sounds amazing, fit finish and the installation were spot on. between the exhaust the Vortech with their Maxflow Race Blow-Off Valve my Mustang turns everyone's head to see whats coming. 5* all the way

            Gunman

            Year: 2003 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            April 03, 2019

            That rumble

            Just had the loudmouth 2 install with the SLP catted x pipe sounds amazing could be a little louder for my taste but that will come when I add headers. Total time for install was a little under a hour and a half with a lift fit was great no complaints

            Charlest

            Year: 2004 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Shop Install

            March 20, 2019

            Great option

            Sounds very nice, not so loud that it shuld only be on a track but enough to say my car means business. I added cat-less bbk x-pipe so it sounds race ready and complements my other mods.

            Shane

            Year: 2003 Submodel: GT

            Helpful (0)

          • 5/5

            Installation Time: Afternoon

            June 09, 2018

            Great exhaust, read this for torque specs

            This system was easy to install, although if you have access to a lift I highly reccomand you use it. I used ramps, and I could have saved myself a lot of time if I had access to a lift. Really lube the hangers before you try to wrestle them off or just remove the 2 bolts and pull the hanger down, but you’ll still need to lube the hangers to really easily get them off. I found it easier to just remove the hangers and do it standing up rather than on my back under the car. I had to call SLP for torque specs on the band clamps and even the guy I spoke with had to call me back later because he wasn’t sure. 25-30 lbs of torque is what the torque should be on the band clamps. I knew I was going to add an X-pipe at some point, so I went with the LM 2, but if I wasn’t, I would have gone with the LM1. This system is much improved over stock, is much deeper, and has a great growl to it, but doesn’t have much more volume to it over stock which is great if you’re looking for a quiet exhaust. Once I add an X-pipe to it, it will be a little bit louder for sure. I certainly don’t want an offensively loud exhaust, but this one is very quiet even for me just as a catback alone.

            TroyC

            Year: 2004 Submodel: GT

            Helpful (5)

          • 5/5

            Installation Time: Afternoon

            April 29, 2018

            Really nice cat system

            Quality cat system that has great tone. Not obnoxiously loud and looks great installed.

            StephenY

            Year: 2003 Submodel: Mach 1

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            April 25, 2018

            Best exhaust on the market

            The exhaust is by far the best on the market! I was running a magnaflow catback system and wanted something different. The install was super easy, I did it in my garage in about 2 hours! Everything lined up well and fit perfectly! Not one thing bad to say! The sound was the best part, being paired with an O/R h pipe; it rumbles at idle and sounds amazing throughout the RPM range! Highly recommend, and thanks again American Muscle!

            MattM

            Year: 2002 Submodel: GT

            Helpful (4)

          • 5/5

            March 26, 2018

            Nice system

            I bought this system for my '99 GT convertible and was a little worried about it being to loud with the top down. I will say this system sounds great and is not overly loud has a nice throaty sound. I installed the system at my shop and took my time just over an hour or so. Very straight forward bolt up. If you are looking for a nice sound but not extremely loud this is the right system even great in a convertible. Great purchase very satisfied!

            ChuckA

            Year: 1999 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            March 07, 2018

            Sounds great and throaty

            I have no cats and at one point no muffler either, the car was too loud so i looked around for a aggressive exhaust that will also muffle the sound some but stay loud and good sounding. So i landed on this and it sounds great after about a week the exhaust broke in and sounded great!!. Would definitely recommend for cars with no cats. If you have cats i think it will be too quiet. Btw i had a lift for my install.

            DarrenF

            Year: 2000 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Shop Install

            February 02, 2018

            Nice!

            Paired this up with an x pipe and they sound great! I would definitely recommend this cat back!

            KevinE

            Year: 2001 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            December 18, 2017

            Nice system

            Easy to install. Toughest part is removing the old system---do not spare the Liquid Wrench (or similar) and put that new metal blade you've been saving in your reciprocating saw. Took my time, did it in my garage with the car on jackstands...probably took 4hrs not counting coffee, snacks, restroom, and a nap (hey, I'm over 60...you kids should be able to knock this out easy and still make the evening cruise). Louder inside the car than stock, but not debilitating...drones a bit right at 2000rpm in 4th, but modulates with minor speed adjustment. Outside the car, noise at idle only marginally above the old clapped out stockers (which is the way I wanted it). Subjectively, the car seems to breathe better.

            Kim

            Year: 2000 Submodel: GT

            Helpful (4)

          • 5/5

            Installation Time: Afternoon

            October 02, 2017

            Loudmouth 2

            Great look,sound and fit.!Had flowmaster 40's but wanted to change up didn't go wrong gave my car a deep rumble and and look.

            Jeremy

            Year: 2003 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            September 29, 2017

            Not as loud as descried

            Fits perfectly. The reviews on the web made it seem like this was a raspy system, it is not. Loud rumble under full throttle. City driving, its respectable but loud enough to turn heads.

            Fabio

            Year: 2003 Submodel: Mach 1

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            September 21, 2017

            Great! Not loud like LM1s

            These are not as loud as LM1s and have a clean, low rumble. It is quite at crusing speeds and loud at WOT. I've had Borla Stingers on my other Mach 1 and wanted to switch it up. The tips are the best on the market for looks, fit was perfect, and sounds great. Perfect for somebody that wants that old fashioned clean rumble. Does sound a lot different on 4Vs compared to 2Vs.

            ChristianH

            Year: 2003 Submodel: Mach 1

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            August 30, 2017

            loudmouth

            the exhaust sounds amazing looks good to was not bad to put in .the hard part was cutting out the old one

            MarkS

            Year: 2003 Submodel: GT

            Helpful (3)

          • 5/5

            Installation Time: Afternoon

            August 19, 2017

            Best sounding Exhaust

            if you are looking for the perfect mix between high quality sound and volume, this is the exhaust for you. The instilation took me a long time but hust because i wasnt working in optimal working conditions and the stock exhaust was a nightmare to get off, but in terms of the SLP install, it took probably about an hour and a half. Im blown away, none of the videos or sound clips do it justice, in person it sounds absolutely amazing, even on the stock H pipe!

            PaulD

            Year: 2002 Submodel: GT

            Helpful (4)

          • 5/5

            Installation Time: Afternoon

            June 01, 2017

            SLP Loudmouth 2

            This exhaust is very throaty paired up with my BBK Xpipe...like music to my ears every time I start it up...If you are thinking about getting a catback this is the one to get!! Thanks AM!!!

            BrandonF

            Year: 2004 Submodel: GT

            Helpful (6)

          • 4/5

            January 07, 2017

            SLP LM2 Cat-Back

            First of all I bought this as it uses stainless steel piping. Install was very easy, rather quick in my opinion. I would not be afraid to recommend encouraging beginners to do this install. I noticed very minimal performance gains by the seat of the pants. The sound is exactly what I was looking for. Has a deep throaty sound that is not extremely loud and almost docile at low rpms. When you get in the throttle it really wakes up and sounds great.

            DC

            Year: 2003 Submodel: GT

            Helpful (4)

          • 5/5

            Installation Time: Less than 1 Hour

            December 10, 2016

            LMII Catback

            I have a 2001 Bullitt with panhard bar. I wanted an exhaust that would not require custom work. The LMII fit perfect and sounds awesome. Idles louder than stock and deeper, and sounds really good through the RPMs. No drone at all. I think I will get the LMI for the track days !

            Ncst8man1999

            Year: 2001 Submodel: Bullitt

            Helpful (3)

          • 5/5

            Installation Time: Less than 1 Hour

            November 30, 2016

            Loudmouth

            2nd one I have had one on my 04 mach one just bought a 03 mach one this was the first upgrade of many comfortable sound till you hit the gas SOUNDS awesome

            skeeterspopa

            Year: 2003 Submodel: Mach 1

            Helpful (3)

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