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

34 Reviews
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  • Item #40000
  • MPN #PC9900
  • Market Price $319.99
  • You Save 11% ($35.00)
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  • 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 stock 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.

Mustang 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

Installation Time: (approx) 2 Hours

Difficulty Level:Advanced mechanical skills required.

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
  • Bullitt - 01
  • Mach 1 - 03, 04
  • Cobra - 99, 01, 03, 04
  • GT - 99, 00, 01, 02, 03, 04

Most Helpful Reviews View All

Overall Rating 4.6/5 Write a Review
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 (30) (0)

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

Read More
Helpful (11) (0)

Customer Photos (9) View All

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Q & A (4 Questions, 8 Answers) Ask a Question

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

MidnightRider Year: 2004 Model: GT

Question Resolved
Good Question (0) (0)
  • 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.

    Helpful (1) (0)

    Best Answer

    My2001GT Year: 2001 Model: GT

Show 2 more answers

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 Year: 2003 Model: GT

Question Resolved
Good Question (1) (0)
  • You could do anything with enough fabrication. It probably wouldn't be worth it. I live in California, and when i get my O/R midpipe i'm going to get it all bolted on, that way when it comes time for smog i just take 30 minutes and swap it out for the stock midpipe.

    Helpful (1) (0)

    Soccerluvr4 Year: 2001 Model: Bullitt

Show 2 more answers

Check Engine Light? Will installing this midpipe turn on the check engine light?

TrueBlueStang Year: 2003 Model: GT

Question Resolved
Good Question (0) (0)
  • TrueBluestang, This will turn your CIL on as there are no cats, this can be fixed by either having a tuner, or the MIL eliminators. This also won't be legal in emission controlled states due to the no cats though. Hope this helps! Forrest

    Helpful (1) (0)

    ForrestS Year: 2002 Model: GT

Show 1 more answer

Reviews (34) Write a Review

  • 5 Stars .76 76%
  • 4 Stars .15 15%
  • 3 Stars .06 6%
  • 2 Stars .03 3%
  • 1 Stars 0 0%

out of 5 stars

29 Customers Recommend this Product

Installation Time:Afternoon

Installation Cost:0-$100

  • Loudness / Volume: 4.322581 4.3/5
  • Exhaust Note: 4.83871 4.8/5
  • Fit & Finish: 4.290323 4.3/5
  • Bang For Your Buck: 4.354839 4.4/5
Filter By Sort By
  • 5/5

    Mac O/R Prochamber

    May 15, 2011

    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 Model: GT Driving Style: Daily Driver

    Helpful (30) (0)

  • 5/5

    scare a ricer to death!!!!!

    May 08, 2012

    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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Orlando, FL, USA

    Helpful (11) (0)

  • 5/5

    Already got complimented.

    June 27, 2011

    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 Model: GT Driving Style: Street / Strip

    Helpful (11) (1)

  • 4/5

    Great product from MAC!

    November 03, 2011

    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 Model: Bullitt Driving Style: Daily Driver 'Stangs I have owned: 5+ East Central Indiana

    Helpful (8) (0)

  • 5/5


    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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Texas

    Helpful (7) (1)

  • 5/5

    Cobra must have

    June 21, 2013

    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 Model: Cobra Driving Style: Daily Driver 'Stangs I have owned: 3

    Helpful (3) (0)

  • 5/5

    Mustang GT prochamber Borla stinger combo!

    July 08, 2013

    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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Miami, FL, USA

    Helpful (2) (0)

  • 4/5

    Definitely recommended!

    January 28, 2013

    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 Model: Mach 1 Driving Style: Street / Strip 'Stangs I have owned: 1 Franklin, ID, USA

    Helpful (2) (0)

  • 5/5


    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 Model: GT Driving Style: Daily Driver 'Stangs I have owned: 1 Las Cruces, NM

    Helpful (3) (1)

  • 5/5

    Pro chamber :-)

    July 15, 2012

    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

    Top 50 Contributor


    Year: 2002 Model: GT Driving Style: Show 'Stangs I have owned: 5+ Oak Forest, IL, USA

    Helpful (1) (1)

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