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Understanding Mustang Exhaust Systems

Written By: Andrew Cilio

Typical Mustang Exhaust Overview

There is no doubt that buying parts for your Mustang's exhaust can be confusing. There are so many brands to choose from, and knowing which parts will work together is crucial to having an exhaust system that is both efficient and great sounding. To make it easier, we’re going to break down the entire system into three main sections: manifolds/headers, mid-pipes, and cat-backs.

It's important to note that 2015+ Mustangs have a slightly different exhaust configuration than your standard Mustang. Looking under an S550, you'll see a suitcase looking thing where your mid-pipe union usually is. This "suitcase" is a resonator, designed to quiet down the exhaust. They come from the factory with an H-style mid-pipe, which gives the system a deep style tone. However, most owners prefer to change their exhausts to their own liking, primarily with an axle back exhaust and a mid-pipe. The whole system weighs in around 70 lbs.

Mustang Exhaust System Diagram

What's The Difference? Exhaust Manifolds vs. Headers

A Mustang's exhaust manifold is connected to the exhaust ports of the engine. They funnel the exhaust gases from the cylinders into a single exhaust passage (the mid-pipe). You will hear manifolds referred to as headers. While they perform the same function, they are not exactly the same. The exhaust manifolds are the factory headers. Usually, they have several holes that merge into a common chamber.

The aftermarket manifolds, or headers, generally have tubes that curve to join the exhaust ports to the pipe. Shorty headers are designed to bolt into the factory manifold location. Long tube headers are usually made for racing applications. Equal length headers can be either shorty or long tube, and the equal length tubes allow for slightly better exhaust flow. It is the curves that make headers a popular modification. This allows the gases to gently slide into the pipe, rather than slamming through the ports.

Stock V6 Mustang Exhaust Manifold
Stock V6 Exhaust Manifold

Shorties, Long Tubes, and Full Length Headers

Shorty Headers vs the Stock Manifold: Shorties are equivalent in size to stock exhaust manifolds. They work with stock mid-pipes as well as standard length aftermarket mid-pipes. Shorty headers are ideal for turbocharged Mustangs and do provide more horsepower and torque than the stock manifolds, but not quite as much as long tubes.

Long Tubes vs the Stock Manifold: Long tube headers do not work with stock mid-pipes because they are too long to bolt up to the factory mid-pipe. Long tube headers require a "shorty" mid-pipe to maintain a consistent exhaust length. Long tube headers and full-length headers are the same thing. Long tubes generally provide more horsepower and torque than shorty headers, but cannot be used with turbocharged motors.

Mustang Long Tube Headers
Long Tube Headers

Mid-Pipes: Between the Manifold and Cat-Back

All Mustang exhausts have a mid-pipe. A mid-pipe is where gases go when they leave the manifold. GT mid-pipes are different than V6 mid-pipes.

  • GT Mustangs: Come stock with a pipe that has an H-formation (H-Pipe)
  • V6 Mustangs: Come stock with a pipe that has a Y-formation (Y-pipe)
  • Some aftermarket mid-pipes come in an X-formation and are called X-pipes

All stock mid-pipes come with catalytic converters, or "cats". Cats remove the contaminants from the exhaust, making them emissions friendly. Aftermarket mid-pipes that are meant to be used off-road or for racing don't have catalytic converters, and are called "off-road H- or X-pipes". Off-road mid-pipes aren't meant for street use and, depending on your state's emissions laws, may not pass inspection.

2005-2010 Mustang GT Stock H-Pipe Versus an Aftermarket Off-Road H-Pipe
Stock H-Pipe Versus an Aftermarket Off-Road H-Pipe

Almost every mid-pipe AmericanMuscle carries are standard length. They will work with stock exhaust setups as well as aftermarket headers and cat-backs. We also carry several shorty mid-pipes, which are used most often in racing applications. These pipes will only work with aftermarket long tube headers. When buying aftermarket long tube headers and short mid-pipes, it is recommended that you stay with the same brand for both parts. In short, mid-pipes can do the following:

  • Changing the pitch of the exhaust note
  • Giving the car more horsepower and torque
  • Removing or replacing the stock catalytic converters with aftermarket setups
  • Easy fitment in combination with long tube or short tube header
1986-1993 5.0L Foxbody Mustang Catted X-Pipe
Catted X-Pipe

Cat-Backs vs Axle-Back Exhaust Systems

What's a cat-back? The cat-back is the system that bolts on behind the catalytic converters. The assembly contains the mufflers and the tailpipes. This is the final destination of the nasty gases from your engine.

What's an axle-back? You may have seen the term “axle-back” mentioned in your research about exhaust systems. Axle-back systems are still the last piece of the exhaust system. They differ from a cat-back because they bolt up behind the mufflers. Axle-backs are simply the piping that connects to the mid-pipe as well as the muffler and tailpipe assemblies.

Did you say axle-back? – What’s nice about the 2005 Mustangs is it allows you to just replace your pipes from the axle, back. Though you can never go wrong with a new aftermarket cat-back.

Flowmaster Cat-Back Exhaust System for 2015-2017 GT Fastback Mustangs
Cat-Back Exhaust System for 2015-2017 GT Fastbacks

Cat-Back Exhaust Summary

  • Add small amounts of power (5-15 HP on average)
  • Go from the catalytic converter all the way back
  • Are louder than axle-backs, but not as loud as long tube headers
  • Offer deep, full exhaust notes without requiring a tune

Axle-Back Exhaust Summary

  • Typically don't add much power (less than 5 HP on average)
  • Go from the rear axle to the back of the car
  • Big improvement over stock, but not as load as doing a cat-back or headers
  • Different systems offer different exhaust notes, from more low-key rumble to waking your neighbors loud

VIDEO: Best 3 Axle-Back Exhausts for S550 (2015-2018) GTs

What Mustang Exhaust Components Work Together?

You've probably come across a ton of information in your research of exhaust, so we'll try to simplify it for you now. These are the basic rules to keep in mind when buying exhaust parts:

  • If you're buying shorty headers or have the factory manifold, you will need to buy a standard length mid-pipe
  • If you're buying long tube headers, you will need to buy a shorty mid-pipe
  • Cat-back and axle-back setups will work with either header/mid-pipe combination
Pypes Dual, Catted Exhaust System Installed on a 1998-2004 Mustang V6
Catted Exhaust System Installed on a 1998-2004 V6

So, What Exhaust Brands Will Work Together?

The majority of the Mustang parts we sell can be used together. This means that you can use BBK parts with Magnaflow parts, and not have any problems with fitment. There is an exception to that rule, though.

Long tube headers can only be used with the same brand shorty mid-pipe. (E.g. SLP long tube headers can only be used with an SLP shorty mid-pipe.)

Other than the exception above, you can mix-and-match parts on your Mustang. When it comes down to it, however, it’s better to be safe than sorry. Stick with the same brand for all of your exhaust parts. If you buy BBK headers, then get a BBK midpipe and cat-back. By doing this, you can be 100% certain that all of your parts will fit together perfectly.

Pypes Long Tube Headers with a Shorty X-Pipe for 2005-2010 GT Mustangs
Long Tube Headers with a Shorty X-Pipe for 2005-2010 GTs

Stock Mustang Piping Sizes and Performance

When piecing together a new exhaust setup, it is important to pay attention to the diameter of the piping as it will play an integral role in your Mustang's performance. When you are flowing more air into your Mustang's engine (whether it is an upgraded intake manifold or a supercharger/turbocharger setup) you will want to increase the exhaust piping size to help scavenge those exhaust gases more efficiently, making more power in the process.

However, it is important to only go as big as you need. If you go with the largest header size you can on an NA car, you may lose some power and back pressure as there is not as much of a need for the larger pipe size. Too large of an exhaust diameter can lower the amount of power an engine can make (in certain situations) because of low exhaust velocity. In basic terms, a water hose will move the same amount of water through a smaller hose diameter at a faster rate. On the other side, if the flow is the same but the pipe is larger, it will not have to flow as fast to move the same amount of water. The same analogy can be utilized towards exhaust. If the engine is not moving enough exhaust, increasing the diameter of the pipe can slow the velocity of the exhaust.

It is also crucial to pay attention to piping size when assembling a full exhaust setup as you may need an adapter to make some exhausts work together if they are different sized exhausts (i.e. a 3" mid-pipe connecting to a 2.5" over axle pipe).

Stock Mustang exhaust piping sizes are as follows:

  • 1979-2004 (Foxbody, New Edge, & SN95): 2.25"
  • 2005-2010 (S197) V6s: 2.25"
  • 2005-2010 (S197): 2.5" with 3" tips
  • 2011-2014 (S197) V6s: 2.5"
  • 2011-2014 (S197) GTs: 2.5" or 3" with 3.5" tips
  • 2015-2018 (S550): 2.25"
Long Tube Catted Headers with 3in Cat-back System for 2015-2017 Mustang GTs
S550 Long Tube, Catted Headers with 3in Cat-back System

Stock Exhaust Routing Under the Body

An IRS equipped vehicle will have the exhaust routed under the axles due to vertical travel of the rear end. Space is also a factor because an IRS rear-end is much more complex and bigger than a traditional live axle (straight axle) setup. IRS Mustangs include the 1999-2004 Cobra and the 2015-2018 Mustangs.

  • 1979-1985 5.0L & 1979-2004 V6s feature a single exit Y-pipe design with the muffler attaching before the rear axle
  • 1987-2004 GTs feature a dual exit H-pipe design with the mufflers attaching before the rear axle
  • 2005-2010 V6s feature a single exit Y-pipe design with a muffler attached after the rear axle
  • 2005-2014 GTs feature a dual exit H-pipe design leading into an axle-back set


Will My Mustang's Exhaust be Street Legal?

Most states will require catalytic converters, so you should always check your state's regulations before purchasing a new exhaust kit for your Mustang. Just because an exhaust kit is listed as “street legal” it doesn't necessarily mean that it is emissions legal for your state.

Maybe you're not worried about keeping your Mustang street legal. Instead, you're looking to rattle your neighbors' windows with the loudest exhaust setup you can find. Making your Mustang louder is going to err on the side of not so legal more often than not. The loudest configuration would be a set of long tube headers, an off-road mid-pipe, and straight through mufflers.

New Edge Mustang Cruising Down the Road

What are MIL Eliminators? Does My Mustang Need Them?

MIL (Malfunction Indication Light) eliminators are used when an off-road mid-pipe (no catalytic converters) is installed. Your car’s computer is programmed to work with cats on the car. When you remove them, the check engine light will come on because of the readings that the car’s computer is receiving from the rear oxygen sensors. The MIL’s essentially trick the car’s computer into thinking that the cats are on the car and that the oxygen sensors are performing properly. MIL eliminators will not bypass a malfunctioning oxygen sensor. They will only shut off the "check engine" light when installed on properly functioning O2 sensors.

Mustang Plug-In MIL Eliminators
Plug-In MIL Eliminators

Do I Need to Purchase Exhaust Hangers?

If you own a 2007 Mustang, we recommend you upgrade the exhaust hangers that are currently on your car. In the 2007 model year, Ford changed the design of their exhaust hangers to a lower quality hanger, and with the new design, we have run into issues with proper exhaust alignment. The new hangers are not a requirement, but we HIGHLY recommend them.

But where are they located? Mustang exhaust hanger locations are the same within a generation. So all Foxbody hangers will be in the same place, s197 hangers will be in the same place, but there is one exception. Single outlet exhausts. If you're converting a V6 to a V8 style exhaust, you'll need an additional hanger and you'll need to modify the rear bumper. Depending on the situation, a different mid-pipe might need to be utilized as well.

Mustang Exhaust Hanger
Rubber Exhaust Hanger

Do I Need a Tune With a New Aftermarket Exhaust?

It depends on the exhaust part you are installing. Cat-back and axle-back kits never require tuning. If you are making changes to your headers or mid-pipe, it is more than likely that you will need a tune to not only calibrate the vehicle for the new parts, but to also maximize the performance you get from them. This is not the case for every application, but it is more common than not.

Mustang BAMA Tuner
Handheld Tuner

Supercharged Mustang Exhaust System Setups

While stock exhaust works for supercharged applications, there are better aftermarket setups. In the best situation, long tube headers, an offroad mid pipe, and a cat-back would be the best setup for a supercharger. However, this can be heavily impacted by emissions and inspections.

Short tube headers are not the best, but prove to be a good supplement over stock exhaust manifolds. Another supplement is a quality set of high flow cats. Replacing these instead of the stock catalytic converters can increase airflow while still being emissions friendly.

Stage 1 Whipple Twin-Screw Supercharger Kit for 2015-2017 Mustang GTs
S550 Twin-Screw Supercharger Kit Installed

Emissions Testing With No Cats - Does It Work?

Emissions testing is unique to each state. While some states do not participate, others go above and beyond to make sure that federal requirements are met. Most states that test do one of 3 tests:

Visual test - The visual test is simply what it says, it is a visual inspection to make sure that catalytic converters are being utilized. This is primarily accomplished by having mirrors that can be used to see underneath the vehicle.

Computer test - This test hs completed by plugging a computer to the OBDII port of the vehicle and reading the output that sensors are giving. Some states allow one set of sensors to read N/A or not ready, with the exception being rear O2 sensors. As a result, O2 sensors must be on and reading correctly in order to pass.

Sniffer test - A sniffer test uses a device that is placed near the tailpipes of the vehicle. It measures the quality of the exhaust being discharged and determines whether catalytic converters are in proper working order.

With those tests, it is generally pretty difficult to pass with rear O2 sensors on. Some states allow for rear O2 sensors to read N/A or not ready, while computer tests can be tricked by using MIL eliminators (on 1996-2004 models).


2011-2014 Mustang GT on a Lift

C.A.R.B. Approved Exhaust Choices

C.A.R.B. stands for California Air Resources Board and has a say in what you can and can't put on your Mustang if you live in one of the states that follow their regulations. Unfortunately, C.A.R.B. compliant states limit how you can modify your Mustang's exhaust, but below we've compiled of list of parts that are C.A.R.B. approved.

2015 (S550) Model Year - Because of where the catalytic converter is positioned, The 2015 GT cannot change headers and be C.A.R.B. legal. The EcoBoost cannot change the downpipe. Cust and clamp or resonator delete setups are the best bet for 2015 GTs and EcoBoosts that need to be C.A.R.B. compliant.  

Compliant Headers

  • EcoBoost - None
  • GT - None
  • V6 - BBK Ceramic Tuned Length Shorty Headers

Compliant Midpipes

  • EcoBoost - Flowmaster Scavenger Series Cut and Clamp Resonator Delete Y-Pipe
  • GT - Heartthrob Cut and Clamp Resonator Delete H-Pipe

2010 - 2014 (S197) Model Years - Shorty headers and manifolds only. Long tube headers will not be C.A.R.B. legal. "High flow" or "off-road" cats or mid-pipes are not likely to be C.A.R.B. legal.

Compliant Headers

  • GT - BBK Ceramic Tuned Length Shorty Headers & JBA Shorty Headers
  • V6 - BBK Tuned Length Shorty Headers

Compliant Exhausts

  • Catbacks and Axelbacks

Special Note: 2010 Mustangs

Compliant Headers

  • GT - BBK Chrome Tuned Length Shorty Headers
  • V6 - BBK Tuned Length Shorty Headers & JBA Shorty Headers

2005 - 2009 (S197) Model Years - Same as 2010-2014. Compliant parts are the same brand and style as the 2010.

1999 - 2004 Model Years - Same as 2010-2014. Compliant parts are as follows:

Compliant Headers

  • GT - BBK Ceramic Tuned Length Shorty Headers & JBA Shorty Headers
  • V6 - BBK Chrome Shorty Headers & JBA Shorty Headers

Compliant Exhausts

  • Catbacks and Axelbacks

Remember to look for the C.A.R.B. EO number when considering exhaust options! If the part has a C.A.R.B. EO, it's C.A.R.B. approved.

NOTE: Mach 1 Exhaust Differences

H and X-pipes for the 1999-2004 Mustang will fit all the 4.6 motors including the Mach 1 and the Cobras. They will fit, however, for the Mach 1 the O2 sensors are in a different location than the Mustang GT location. Below is a picture a fellow enthusiast drew up with all the different color arrows of a Mach 1 Mustang labeling the location of the oxygen sensors, and the other is the picture of the regular GT H-pipe. As you can see the Mach 1 O2 sensors are located farther away than the GT locations, so the Mach 1 will need O2 extensions. 

Mach 1 Mustang Oxygen Sensor Locations
1999-2004 Mustang GT Oxygen Sensor Locations
Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, GT, V6, Cobra, ShelbyGT500, Mach1, Bullitt, Boss, LX, SVO, EcoBoost, ShelbyGT350