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Flowmaster Catted H-Pipe (99-04 GT)

AmericanMuscle no longer carries the Flowmaster Catted H-Pipe (99-04 GT). Please check out 1999-2004 Mustang H-Pipes for an updated selection.
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Features & Details

  • Improves Exhaust Flow and Sound
  • Classic Muscle Car Rumble
  • 2-1/4" Mandrel-Bent Stainless Steel Tubing
  • High Flow Catalytic Converters Included
  • 49 State Emissions Legal
  • For Use with Stock Manifolds or Shorty Aftermarket Headers
  • Fits 1999-2004 GT and Bullitt Mustangs
Improves Flow For More Power. Improve the horsepower and torque of your 4.6L GT Mustang by replacing those restrictive stock cats with a brand new Flowmaster H-Pipe that features high-flow catalytic converters. The Flowmaster high flow catted H-Pipe will significantly improve your Mustang's exhaust flow for a notable increase in horsepower and torque.

Muscle Car Rumble. This free flowing Flowmaster Mid Pipe will not only improve performance, but it will also add a deep muscle car rumble to the sound of your exhaust with its classic "H" crossover pipe design.

Quality Construction. Constructed in the USA from durable 2.25" 16 gauge 409 stainless steel tubing for it's corrosion resistant properties this Flowmaster H-Pipe features four high flow catalytic converters, two main cats and two pre-cats. The included catalytic converters feature a durable ceramic substrate material making them perfect for naturally aspirated applications.

49 State Legal. The included catalytic converters meet or exceed USEPA standards and are 49 state emissions legal. They are not legal for use in the state of California.

Application. This Flowmaster High Performance Catted H-Pipe is designed to be a direct bolt-on replacement for the 1999-2004 4.6L V8 Mustangs, including the GT and Bullitt models with either aftermarket shorty headers or the stock manifolds installed.

Technical note: 2004 Mustangs require the use of 24" O2 sensor plug-in extender wires.

Fitment: 1999 2000 2001 2002 2003 2004 Details

MPN# 2020027

CA Residents: WARNING: Cancer and Reproductive Harm -

What's in the Box
  • (1) Catted H-pipe
  • (2) clamps
Installation Info
Tech Specs
Mid Pipe Specifications
Style Mid Pipe: Standard length "H" Type Headers Required: Shorty or stock manifolds
Piping Material: Stainless Steel Piping Size: 2.25"
Catalytic Converter: "Yes" Fitment: 1999-2004 GT & Bullitt Mustangs
Will it fit my Mustang?

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Questions & Answers (7)

5 Top Rated Questions

Will this fit with the slp loudmouth catback?

  • When mixing different manufacturers exhaust pieces you may have to do slight modification for proper fitment. There may be a slight length difference, as most manufacturers design their systems to work with their own components or with the original equipment ones.

Helpful (0)

Is this legal for road use in CA?

  • This Flowmaster Catted H-Pipe has not been tested or approved by the California Air Resource Board meaning it is not legal for use upon roads in the state of California.

Helpful (0)

Do the catalytic converters have CARB compliant numbers displayed on them that would be clearly visible during a routine visual inspection? Are there any fit issues with BBK shorty headers?

  • These catalytic converters do not have a CARB compliant number as these will not pass California CARB regulations.As far as fitment with the BBK headers, I would recommend the BBK catted mid-pipe as long as it will be CARB compliant.

Helpful (0)

Can I use Flomaster H-pipe with BBK Long tube headers on my 2001 GT 4.6L or should i use BBK shorty headers. I am looking for performance.

  • This Flowmaster Catted H-Pipe will only fit with factory length headers, and long tube headers would not fit correctly with this h-pipe. We would highly recommend a shorty/stock-length header, preferably the same brand for the mid-pipe and the header.

Helpful (0)

I recently purchased a Pype's off road H that was sold for the GT that fit my Mach 1 perfectly. Will this Catted H also fit the 2003 Mach 1

  • Unfortunately this will not fit a 2003 Mach 1.

Helpful (0)
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2 More Questions
HP gain? How much horsepower does this exhaust add? 1 answer
Would I install this together with the flowmaster catback exhaust system you have on your site as well? 1 answer

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Customer Reviews (3) Write a Review

Overall Rating 5

out of 5 stars

Installation Time:Shop Install

Installation Cost:$100-$250

  • Loudness / Volume 4.666667 4.7
  • Exhaust Note 5 5
  • Fit & Finish 5 5
  • Bang For Your Buck 4.666667 4.7

  • 5/5

    Installation Time: Shop Install

    August 10, 2018

    needed new cats

    needed new catalytic converters. gives the car a deeper tone. good quality part. shop install was straight forward.


    Year: 2002 Submodel: GT

    Helpful (4)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    May 23, 2013

    Flowmaster Catted H-Pipe

    Passed Colorado emissions. Good sound with Bassani Cat Back exhaust. No drone. Fitment with Bassani cat back required some cutting & welding to line up the rear exhaust tips. Very pleased with performance & quality.


    Year: 1999 Submodel: GT Denver, CO, USA

    Helpful (8)

  • 5/5

    Installation Time: Shop Install

    Installation Cost: $100-$250

    April 02, 2013


    Adds a little bit and made a better sound over stock highly recommend it!!


    Year: 2003 Submodel: GT

    Helpful (7)

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