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Understanding Mustang Exhaust Systems

Written By: Andrew Cilio

There are three main components to the exhaust system, and all Mustangs have the same set-up, regardless of generation. We'll break down each variation of the systems, so you'll have a better idea what you'll want for your Mustang.

American Muscle

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.

Mustang Exhaust Breakdown Diagram

Whats The Difference? Exhaust Manifolds vs. Headers

Exhaust manifolds are 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.

Mustang Stock Exhaust Manifold

Shorties, Long Tubes, and Full Length Headers

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 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 Header Set

Mustang Mid-Pipes 

All Mustang exhausts have a mid-pipe. This 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.

Almost every mid-pipe AmericanMuscle carries are standard length. They will work with stock exhaust set ups as well as aftermarket headers and catbacks. 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.

Mustang X-Pipe

Mustang Cat-back Exhausts

The cat-back 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.

You may have seen the term “axleback” mentioned in your research about exhaust systems. Axleback systems are still the last piece of the exhaust system. They differ from a catback because they bolt up behind the mufflers.

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

Catback Exhausts

  • 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 now as loud as long tube headers
  • Offer deep, full exhaust notes without requiring a tune

Axle-Back Exhausts

  • 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
Mustang Cat-back Exhaust System

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
  • Catback and axleback setups will work with either header/mid-pipe combination
Mustang Catted X-Pipe with Connecting Pipes

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 catback. By doing this, you can be 100% certain that all of your parts will fit together perfectly.

Piping Size 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.

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).

BBK Mustang Shorty Headers

Will my Mustang's Exhaust be Street Legal?

Most states will require catalytic converters, so you should always check your states 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.

New Edge Mustang on the Street

Do I Need MIL Eliminators?

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

Do I Need to Purchase Exhaust Hangers?

If you own a 2007 Mustang, we recommend that 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.

Mustang 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

Supercharged Mustang Exhaust Setups

While stock exhaust works for supercharged applications, there are better aftermarket setups. In the best situation, longtube headers, an offroad mid pipe, and a catback 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 provide 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.

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).