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How to Upgrade Your 2015-2017 Mustang's Exhaust System

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Upgrading your S550 Mustang's exhaust is the easiest way to double-down on the fun factor. Change the pipes, change the sound and put the pedal to the floor--it will be the most fun you've had in your Mustang yet.

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Uncorking the factory exhaust allows your Mustang to breathe better, operate more efficiently, lose some weight (the stock system weighs in around 71lbs!) and most importantly, gives it that iconic Mustang sound. The 2015+ Mustang may have an independent rear suspension reworked exhaust system, but many of the core components are very similar to the S197 (2010-2014) Mustangs. This guide lays out the core components and gives advice on upgrading from your stock exhaust to something much more fun.

American Muscle

What Makes Up Your Mustang's Exhaust

There are several basic sections of a Mustang’s exhaust system. Each plays a key function in allowing your Mustang to make power and pass emissions from the factory. Starting from the engine and working your way back, there are the manifolds or headers if they’ve been upgraded. The mid-pipe follows next and is commonly referred to as a downpipe on 4 cylinder applications. After the mid or downpipe is the cat-back, which connects the rest of your exhaust system to the axle-back. This modular system makes it easy to replace each key component one piece at a time.

From the engine back:

  • Exhaust manifolds (headers)
  • Mid-pipe
  • H-Pipe or X-Pipe For GT or V6. Downpipe for the EcoBoost Mustang
  • Cat-back or axle-back depending on your preferred application

EcoBoost Mustangs:

  • Sadly, only the V8 engines have header options
  • High flow catted downpipes are available for better flow while keeping your 'Stang street legal
  • If your EcoBoost is purely track oriented, off-road, cat-less downpipes are also available
  • Cat-backs replaced everything after the catalytic convertor and vary in loudness
  • Axle-backs are cheaper than full cat-backs and are essentially muffle replacements for your Mustang
2015 Foose Mustang California Reveal

Upgrading Your Stock Exhaust Manifolds

Why would you want to replace your Mustang's factory manifolds? Because they’re restrictive, and they prevent your Mustang from performing at its best. On a GT you can replace the stock manifolds with long tube headers. One of the factory catalytic converters is built into the manifold on the GT, so the shorty headers available for the GT require welding to make them fir. Long tube headers offer more horsepower over shorty headers, so they’re the best choice for a performance minded GT owner. Those of you who live in emissions restrictive states will be forced to keep the stock manifolds, since long tube headers often times will not pass emissions testing. Unfortunately for EcoBoost owners, the EcoBoost exhaust manifold is cast into the cylinder head and can’t be replaced. Since the EcoBoost is a turbo motor, it has a special exhaust manifold that re-circulates the exhaust gasses to the hot side of the turbo before going out the tail pipes. Because of the constricted space to do this, the OEM piece is nearly efficient as one can get, and thus no aftermarket designs have yet surfaced.

Under the Hood of an EcoBoost - the Turbo Manifold
EcoBoost Stock Turbo Manifold

Ditching the Mid-Pipe or Downpipe

  • Change the pitch of the exhaust note.
  • Give your Mustang more horsepower and torque
  • Remove or replace the stock catalytic converters with aftermarket setups
  • Easy fitment in combination with long tube or short tube headers

The factory mid-pipe on the S550 houses a HUGE resonator. It keeps your Mustang quiet, and it restricts exhaust flow. Removing the resonator and installing an X or H-pipe will increase the flow of your Mustangs exhaust and will give you a completely different sound. An H-pipe will give you a deep, classic muscle car sound, and an X pipe will give you a raspy, race oriented sound. It’s difficult to remove the catalytic converters on the GT unless you install long tubes, since one of the cats is welded to the manifold. It is possible to cut the cat off and install an adapter which will allow you to install an off-road H or X-pipe. 

2015-2017 GT Mustang with a Cut-and-Clamp H-Pipe
GT with a Cut-and-Clamp H-Pipe

EcoBoost owners have it much easier than GT owners when it comes to deleting the cats. With about an hour’s worth of work, you can replace your stock downpipe with an off-road downpipe, or a downpipe with high-flow cats. Both offer an increase in flow and performance over the factory cat and downpipe. Alternatively, if you just want to delete the resonator on your EcoBoost, you can purchase a resonator delete Y-pipe to lose that big box! 

The first thing to notice about an aftermarket downpipe is the size. Nearly all of them feature a 3” opening and then taper down to 2.5” on the outlet side. Catalytic equipped downpipes will feature a higher flowing cat than the stock unit, or if you select an off-road downpipe (which technically is not legal in many states), it will have no catalytic converter all together. Furthermore, since aftermarket companies have less variables to address (namely cost and cross-platform compatibility), they are able to manufacture a unique piece that really conforms to the Mustang; minimizing bends, avoiding kinks etc. that can hamper flow. All said and done, an aftermarket downpipe can and will net a noticeable amount of horsepower and torque to the rear wheels.

EcoBoost Mustang Catted Downpipe
EcoBoost Catted Downpipe Kit

Mac's Prochamber Mid-Pipe

There is one midpipe that isn't truly an X-pipe or an H-pipe, but its own unique design. Exhaust manufacturer MAC Performance has been making a ‘Prochamber’ starting with the 2005 Mustang models. When the 2015 models came out, MAC made no exception and started producing them for the newest generation of Mustangs. While it is only available in their cat-back package, a prochamber is essentially a box that is hollow on the inside. This allows the exhaust to exit the tailpipes with a sound that is not only deeper, but also throatier than similar H and X-pipes.

S550 Mid-Pipe Replacement Options

GT Owners Can:

  • Install a cut and clamp X or H-pipe to improve sound and flow
  • Have the cats cut out and an adapter welded in to allow installation of an off-road X or H

EcoBoost Owners Can:

  • Install a catted downpipe
  • Install an off-road downpipe
  • Install cut and clamp Y-pipe to delete the resonator

Catted Exhaust vs. Off-Road

Catted Exhaust

  • Pass emissions testing
  • Keeps noise levels acceptable 
  • Decreases exhaust fumes
  • No risk of fine

Off-Road Exhaust

  • Do not live in an emissions restrictive state
  • Seeking an aggressive exhaust note
  • Do not mind increased exhaust fumes
  • Are not concerned with potential fines
Cat-less Mustang Downpipes
Cat-less Downpipes

Finding the Perfect Sound: Cat-Backs

Cat-backs and axle-backs are the key to giving your Mustang the perfect sound. By changing the mufflers you can get a range of different sounds from your exhaust. Most cat-backs come with an X or H-pipe, so you could skip replacing the mid-pipe by itself and just go with a cat-back. This would allow you to replace the mid-pipe, over axle pipes, and the axle-back giving you the best exhaust flow and the perfect exhaust note! Think about installing a cat-back before making your decision on the mid-pipe. It will prevent you from ending up with an extra mid-pipe and going through the installation process more than once.

Heartthrob Cut-and-Clamp X-Pipe Installed on a 2015-2017 GT Mustang
Cut-and-Clamp X-Pipe on a GT

With the EcoBoost, the downpipe connects to a resonator which then splits the exhaust into a dual setup, each side having its own muffler before finally venting into the atmosphere. Aftermarket systems ditch the resonator, replacing it with a Y-assembly and replace the stock mufflers with higher flowing, louder units. Certain cat-back systems may use straight through mufflers, which typically flow the best. While these mufflers undoubtedly sound amazing, straight through style mufflers may be illegal in some states (so be careful!).

A cat-back system is not only going to give your Mustang extra bark (systems vary from marginal extra bark to significant extra bark – aka VERY loud) but extra bite too. Less restriction throughout means a few more ponies at the wheels. The cherry on top: installing these kits is usually a breeze. The majority of them are a direct fit, bolt-on replacement. Simply drop the old pipes and wrench in the new one.

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

Utilizing Axle-Backs for Different Sounds

If you aren’t feeling the whole cat-back deal, but want a bit more of a raw sound, consider an axle-back kit. These kits simply replace the stock muffler and tailpipes with a direct bolt-on aftermarket variety. Available styles range anywhere from moderately loud to pretty damn loud and typically cost just a fraction of what the full cat-back system sells for. Because the resonator is still part of the exhaust line an axle-back kit will never emit the same level of rawness that a cat-back system is capable of, nor will it free up the same amount of horsepower. Regardless, for those who want a more aggressive sound but without breaking the bank, it’s difficult to look over an axle-back. Just keep in mind, like cat-back kits, some of these systems may come with straight through mufflers which may or may not be legal in all states.

Msutang Axle-Back Exhaust System
Axle-Back Exhaust System
Fitment includes: 2015, 2016, 2017, 2018, GT, V6, EcoBoost, ShelbyGT350