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MAC Off-road Pro Chamber Mid Pipe (99-04 4.6L)

Market Price $371.40 You Save 13% ($48.45)
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  • Item 40000
  • MPN# PC9900

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Features & Details

  • Improves Exhaust Flow for More Power
  • Unique Pro Chamber Crossover Design
  • For Off-Road, Track Use
  • 2.5" Mandrel-Bent Aluminized Steel Tubing
  • Fits 99-04 GT, Bullitt, Mach 1 & SVT Cobras
Increase Exhaust Flow. Get rid of those power robbing factory catalytic converters and uncork your Mustangs hidden power with a MAC Performance Off-road Mid-Pipe. Featuring their exclusive Pro Chamber style crossover and free-flowing mandrel-bent piping, this high performance Mid Pipe will dramatically improve exhaust flow for more horsepower and torque.

Aggressive Muscle Car Rumble. This free flowing MAC off-road Mid Pipe not only increases the horsepower and torque of your Mustang, but with its unique Pro Chamber cross over design it adds a more aggressive muscle car rumble to the sound of your exhaust, that the standard H-Pipe just can't match.

High Quality Construction. Mandrel bent from durable 2.5" steel tubing so there are no kinks to rob you of power, this MAC Performance Mid Pipe has been hot-dip coated with aluminum-silicon alloy to aluminize the steel to protect against corrosion and rust.

Application. This MAC Performance Pro Chamber Off-road Mid-pipe is designed as a direct bolt-on for the 1999-2004 4.6L Mustangs, including the GT, Bullitt, Mach 1 and SVT Cobra Models with either aftermarket short tube headers or the factory manifolds and a dual catback exhaust installed. Intended for off-road, track use only, does not include catalytic converters.

Technical note: 2004 Mustangs require the use of 24" O2 sensor plug-in extender wires. This MAC Performance product is intended for off road use, and is not legal for use in emission restrictive states.

Fitment: 1999 2000 2001 2002 2003 2004 Details

What's in the Box
  • (1) Mid-pipe
  • (2) Down Pipes
  • (8) Threaded Studs
  • (8) Nuts
Installation Info
Tech Specs
Mid Pipe Specifications
Style Mid Pipe: Standard length Type Headers Required: Shorty or Stock Manifolds
Piping Material: Aluminized Steel Piping Size: 2.5"
Catalytic Converter: "No" - For off-road use only Fitment: 1999-2004 GT, Bullitt, Mach 1 and Cobra Mustangs
Will it fit my Mustang?
  • Bullitt - 01
  • Mach 1 - 03, 04
  • Cobra - 99, 01, 03, 04
  • GT - 99, 00, 01, 02, 03, 04

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Most Helpful Reviews

Mac O/R Prochamber

I have a 2003 Mustang GT and lets just say everybody knows when I am coming!!! This O/R Prochamber combined with Flowmaster 40s is a very deep aggressive tone that is perfect for a Mustang. I'd recommend ...

Read More
Helpful (31)


overpriced almost every other site that has the prochamber sells it for 249. same with the mac catback can find it for 10-20 dollars cheaper on stangmods.....usually I only go with AM but not this time. ...

Read More
Helpful (17)

Overall Rating 4.6 out of 5 stars
Read All 55 Reviews

Customer Photos (14) Submit Your Photo

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8 Questions / 9 Answers

Ask a Question

Pairing up with hig flow cats i have flowmasters welded into my stock mid pipe, and the sound is nice, but i need a little bit more umph. Unfortunately in MA, I need to have cats to pass inspection. Would i be able to have hig flow cats welded into this mid pipe, and will it still give me that extra umph for exhaust tone and loudness with the high flow cats in? Thanks in advanced guys. And no, i do not want to switch mid pipes every year just for inspection!


  • jay281GT, Depending on the length of the aftermarket cats you choose, they should fit!, the sound change will be minimal with high flow, but a little quieter in my opinion. Any reliable exhaust shop should be able to make the necessary changes for you, if you do not have any local to you, We do have a few catted mid-pipe options for you! Hope this helps, Forrest


Show 2 more answers Helpful (1)

I was wondering will i need o2 sensor extensions and mil eliminators to install this any help would be appreciated


  • It depends on the year of your Mustang. If you have an 03-04 Mustang GT you will need the extensions. If you have a previous year then you don't. My 2001 GT sat perfectly, stretched but just the right amount.


Show 2 more answers Helpful (1)

After installing this midpipe. My exhaust is only about 2 inches off the ground. What can i do to make it sit closer to under the car.


  • With issues with exhaust fitment on the car, we usually recommend taking to a professional exhaust shop to check and see what the issue is, whether it be a bent hanger or a bent mounting point for the exhaust.


Helpful (0)

I'm seeing the piping on this mid pipe is 2.5". Will it fit flush and not cause any exhaust leak combined with the Mac 3" catback exhaust?


  • If you are asking about the MAC cat-back exhaust we offer (item 40047) then the mid pipe should fit without issue. If the exhaust you have does have 3 inch piping, unless the pipe has a step down to 2.5 inches, it likely will not have good fitment. Link for good fitting cat-back below. MAC Cat-Back Exhaust:


Helpful (0)

I see a circular type adapter in the picture of the various hardware components. What is this and where exactly does it go? Any other need to knows or tips for install?


Im running a slp lm1 cat back im worried if this mid pype is going to make it quiter cause im trying to go for something to make it louder but also not too raspy but still sound good and turn heads.


  • The MAC Off-road Pro Chamber Mid Pipe (99-04 4.6L) will be a off-road designed eliminating the cats making for a great sound increase to your car.


Helpful (0)

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Customer Reviews (55) Write a Review

Overall Rating 4.6

out of 5 stars

Installation Time:Afternoon

Installation Cost:$100-$250

  • Loudness / Volume 4.392157 4.4
  • Exhaust Note 4.784314 4.8
  • Fit & Finish 4.27451 4.3
  • Bang For Your Buck 4.392157 4.4

  • 5/5

    May 15, 2011

    Mac O/R Prochamber

    I have a 2003 Mustang GT and lets just say everybody knows when I am coming!!! This O/R Prochamber combined with Flowmaster 40s is a very deep aggressive tone that is perfect for a Mustang. I'd recommend this product to anybody!

    Corey Miller

    Year: 2003 Submodel: GT

    Helpful (31)

  • 5/5

    May 27, 2011


    overpriced almost every other site that has the prochamber sells it for 249. same with the mac catback can find it for 10-20 dollars cheaper on stangmods.....usually I only go with AM but not this time. I know that AM is by far the quickest with getting you your stuff but I'll wait the extra 2 days and save my 40 bones!


    Year: 2003 Submodel: Mach 1

    Helpful (17)

  • 5/5

    Installation Time: Afternoon

    May 08, 2012

    scare a ricer to death!!!!!

    great product! fits very well. sounds AMAZING!!! after i put it on i went out for a test run. pulled up to a traffic light and a civic with a f#$% can pulled up next to me and reved his engine, so i reved mine to 6000 rpm. he rolled up his window and pulled away VERY SLOWLY! lol!


    Year: 2004 Submodel: GT Orlando, FL, USA

    Helpful (13)

  • 5/5

    June 27, 2011

    Already got complimented.

    This mid-pipe is amazing. It sounds like an old school hot rod. I looked at X and H pipes and decided to go with the Prochamber. I'm glad I did. Today I had some guy next to me ask me to rev the car while he pulled out his cell phone to capture the sound... The install was easy once I got the passenger side bolts off. I did it myself in the garage with jackstands. The fit was perfect and everything lined up just right with minimal adjustment needed.


    Year: 2000 Submodel: GT

    Helpful (11)

  • 4/5

    Installation Time: Less than 1 Hour

    November 03, 2011

    Great product from MAC!

    I had this pipe installed at my buddys shop (JC Motorsports) on my 01 Bullitt. I have the stock manifold and stock cat back exhaust still on the car. I personally think it sounds great, i wasnt looking for it to be alot louder, i just wanted rid of the cats. I def noticed more low end power- no doubt about that. but if your wanting a much louder sound go with the H or X pipe. Again, i didnt want it much louder- i just wanted some power freed up. I also bought the mil eliminators so no check engine light for me! It was not difficult at all to install, does not come with directions, but i would say its pretty obvious how to install it. After it was on, a few adjustments had to made to eliminate some exhaust leaks- but they were fixed pretty easily. All in all, a great product- the only reason i did not rate it completly 5 stars is i think it is very pricy. a comparable X pipe is $50 dollars cheaper, but i dont like the "raspy" sound and cackle of those.I would definatly buy again. And I am a repeat customer with american muscle- Excellent customer service- and prompt shipping! Had the pipe in under 72 hours from the min i purchased it!


    Year: 2001 Submodel: Bullitt East Central Indiana

    Helpful (9)

  • 5/5

    Installation Time: Less than 1 Hour

    November 01, 2011


    I had a UPR o/r X pipe on my stang with the 40 series Flowmasters and I loved it at first but my car is a daily driver and I got real tired of the "look at me loud" that the x pipe gave me so I swapped for the Mac Prochamber for that nice muscle car sound and I love it! Its very well mannered below 3000 rpms but once you step on the loud pedal man it screams! I get compliments from everyone and they tell me they like it more than your typical dime a dozen x piped Mustangs. I also did notice the engine breathes better compared to the stock midpipe that I had on while I waited for the Mac to come in the mail. Only con was it is a little pricey for a midpipe but its a good thing because not very many people will probably have this setup!


    Year: 2003 Submodel: GT Texas

    Helpful (7)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: 0-$100

    July 08, 2013

    Mustang GT prochamber Borla stinger combo!

    I used to run a UPR catted x pipe with Borla stingers and it was way too loud with tons of drone. In my opinion the prochamber sounds best with stingers and is the quietest mid pipe when compared to off road H's or X's. Definitely noticed an improvement in performance as well. Thanks AM!


    Year: 2001 Submodel: GT Miami, FL, USA

    Helpful (4)

  • 5/5

    Installation Time: Afternoon

    June 21, 2013

    Cobra must have

    Perfect sound with stock manifolds and borla stingers. Just a mean muscle car rumble that turns heads and earns compliments everywhere. Had xpipe and was too raspy. Pro chamber perfect blend of sound and rumble


    Year: 2004 Submodel: Cobra

    Helpful (3)

  • 5/5

    Installation Time: Less than 1 Hour

    September 03, 2011


    I have a 2001 Mustang GT. Basic bolt on and full Flowmaster exhaust. Did my homework, looked everywhere to see which was better (x-pipe, h-pipe, or pro chamber). Based off reviews, i went with the pro chamber, and let me tell you, could not be happier. Get nothing but compliments, this with flowmaster, is how a mustang should sound. Do you homework, research what you want, and if this is the one you choose, then GREAT choice. Thank AM!!!


    Year: 2001 Submodel: GT Las Cruces, NM

    Helpful (3)

  • 5/5

    Installation Time: Less than 1 Hour

    November 20, 2016

    Mac ProChmaber

    I received the mac prochamber within a week of ordering it and I love in Cali so thanks AM. Package was in great condition and it was a flawless delivery. My back was out so I had the shop install it for me. Easy install they said. Had them attached the MIL Eliminators as well so no CEL for me. The sound difference is dramatic. Not really any noticeable drone. Louder cold start and thumpy idle. Anything past 2000 RPMs and it screams, similar to an X pipe. Nice low and mid range power increase. I do have this paired up with the SLP LM1 catback as well. I do feel vibrations against the subframe but I believe that to be an install issue not a product one at all and one I'm sure it will be easy to fix. Overall it's a great product. Thanks AM!


    Year: 2003 Submodel: Mach 1

    Helpful (2)

  • 4/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    January 28, 2013

    Definitely recommended!

    Great product, kind of pricey for what comes in the box, but i'm loving the sound my car puts out, so I can't complain too much. Paired this up with some Borla Pro Xs and 2.5 all the way out. Got the sound i was looking for. Loudness and exhaust note will be determined by the type of muffler you chose to install. Fit and finish, i would recommend getting some O2 adapters. the right side fit great and had some slack, but the left side was pretty tight, but it did fit. it's all up the buyer on that one. Overall rating is "Good".


    Year: 2003 Submodel: Mach 1 Franklin, ID, USA

    Helpful (2)

  • 2/5

    Installation Time: Afternoon

    May 24, 2017


    While previous products from MAC have been exceptional, this kit was all wrong. Does not fit the studs in stock exhaust headers. Incorrect gasket, should come with a metal flanged gasket. Down pipe to hbox bent wrong and is too short had to pull exhaust off of hangars to fit. Threaded holes in flanges and bolts provided are incorrectly sized had to rethread. Still fighting exhaust leaks and waiting for parts. Hoping to have everything together by the end of the week


    Year: 2004 Submodel: GT

    Helpful (1)

  • 5/5

    August 26, 2016

    That sounds awesome

    Nothing like a MAC Prochamber with a Flowmaster Catback. My favorite Mustang sound!!!


    Year: 2002 Submodel: GT

    Helpful (1)

  • 4/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    April 11, 2015

    Clean Exhaust note

    I had the stock h pipe with the rear cats removed with slp lm 1 and it sounded real good at low rpm but after 3k it was nothing but bah bah bah not that good but now with the pro chamber it cleaned it up it's a little bit louder than before but not crazy loud but they will hear you coming.The only down side is I don't know if it's just in my head but maybe I lost some low end torque but it does poll good in the high end so it's a trade off for a little torque for sound and hp and I recommend this mide pipe


    Year: 2002 Submodel: GT Las Vegas Nv

    Helpful (1)

  • 4/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    November 25, 2014

    Had to cut/weld or would have had to return for replacement.

    I was the lucky guy who got the Pro Chamber that won't fit with stock manifolds and Magnaflow catbacks. I had the best shop in my area do the install so it's not like they didn't know what they were doing. Since the old Mac off-road H was already off, I just had them cut the one pipe with a bad angle and turn it slightly and re-weld it. Other than that, I love the tone and decrease in volume/drone! Still glad I bought it, not glad instead of $40 install, it went to $135 for the time they had to spend on it. And yes, I watched the entire process and have advanced mechanical skills.


    Year: 2004 Submodel: GT Long Beach, MS, USA

    Helpful (1)

  • 5/5

    Installation Time: Afternoon

    April 27, 2014

    Best Mid Pipe Design Hands Down...

    2000 Mustang GT I changed out my BBK off road X-pipe to the MAC Prochamber. I couldn't stand that rattling/exhaust leak sound I had gotten out of the x-pipe any longer. It has the deep sounding characteristics of any off road pipe, but smoother tone overall. It does cost more, but in my opinion its very well worth it. The fit and finish is great, it actually fits closer to the bottom of the car. Helps out alot on lowered cars. Because it fits closer, I had to bend up the mounting plate that held the connectors for the downstream o2 sensors and zip tie to secure wiring, no big deal. BTW, it does come with a gasket for the passenger side exhaust manifold, and the reducer to seal the driver side manifold. Something i didn't get with the BBK...


    Year: 2000 Submodel: GT Darlington, SC, USA

    Helpful (1)

  • 5/5

    Installation Time: Less than 1 Hour

    July 15, 2012

    Pro chamber :-)

    This is what a mustang GT supposed to sound like , nice deep rumble when u hit the gas the sound of an animal comes alive , thx again AM for another great product and speedy delivery


    Year: 2002 Submodel: GT Oak Forest, IL, USA

    Helpful (1)

  • 3/5

    Installation Time: Afternoon

    September 04, 2017

    the noise its great buuut...

    the sound is 100 better and the exhaust note is just right but the fitment is questionable, the flange that connects to the manifold on the driver side is way too big that no matter how much you tighten it, it won't seal and it's quite loose. Just keep in mind that welding might be in order for better fitment. Also, either storage or handling could be better the connection tips bend really easy. Finally, for what it is, it's a little pricy and the craftsmanship is wanting. If you are looking for noise go for the x pipe its cheaper, equal performance and noise


    Year: 2001 Submodel: GT

    Helpful (0)

  • 5/5

    Installation Time: Afternoon

    July 19, 2017

    Please read!!

    I replaced my factory cat back with Borla Ataks. I wanted to be a little bit louder so i went ahead and purchased the BBK off road X-pipe, worst mistake i ever made. So i purchased the Mac Prochamber. This on the other hand has easily been one of the best upgrades i have made to my car! I got the loudness i wanted and get thumbs up for it. The BBK x-pipe all i got were dirty looks and people hating it. Overall i recommend this Prochamber to anyone!!


    Year: 2004 Submodel: GT

    Helpful (0)

  • 5/5

    Installation Time: Afternoon

    July 17, 2017


    This is exactly what my 04 cobra needed. I originally put the slp loudmouth 1 catback on it and it wasn't enough. So I did my research and bought the Mac prochamber and wow what a difference my car sounds awesome and gets plenty of compliments.


    Year: 2004 Submodel: Cobra

    Helpful (0)

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