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What to Upgrade When Modifying Your Mustang's Exhaust System

One of the first modifications any Mustang owner makes to his/her ride is swapping the factory exhaust for an aftermarket one. Once you do upgrade the exhaust, you’ll want to make sure you get the most out of it by upgrading the other various supporting systems on your Mustang. This guide will go over how you can maximize the performance of your exhaust system with supporting mods.

American Muscle

How is My Mustang’s Exhaust System Held Back? 

The exhaust system scavenges all of the spent gas and fumes from the engine and channels them out of the car. Upgrading the exhaust system allows all of the gases to exit the car much more efficiently. Once you upgrade every part of your exhaust system, you eventually hit a wall with your performance. 

The main areas where your exhaust system is held back is in: 

  • The intake
  • The fuel injectors
  • The cylinder heads
  • The cam shafts

Another way to think about it is once you maximize what you can take out of your Mustang’s engine (the exhaust) you need to maximize what your Mustang can put into the engine.

What Does Upgrading My Mustang’s Intake Do to the Exhaust?

Upgrading the intake allows your engine to suck in more air. The intake can be just the filter and the air tube (also known as the cold air intake), or it can also be the manifold itself. Either way, the stock intake cycle, from filter to manifold and including the throttle body, is choking up your engine. 

Replacing the intake system from the filter to the manifold will allow your engine to take in a considerably larger amount of air, which in turn will help your Mustang to make more power.

2015-2017 Mustang GT with a Cold Air Intake
2015-2017 GT with a Cold Air Intake

How Will Fuel Injectors Help My Mustang’s Exhaust System?

In the simplest of terms, power is made by mixing air and fuel, so once you have upgraded how much air your engine can take in and expel, you’ll want to upgrade how much fuel your engine can suck in. Going to a higher rate fuel injector will give your Mustang much more power when combined with the other previously mentioned modifications. 

When you don’t upgrade the fuel injectors, but you do upgrade the exhaust/intake cycle, your engine will starve for fuel in the high-mid range up to redline. There is no use in upgrading your engine to take in all of that extra air without being able to throw some extra fuel into the mix as well.

How Will Upgrading My Mustang’s Cylinder Heads Help the Exhaust? 

Going off of the previous section, your cylinder heads dictate how much fuel and air your Mustang can mix together to make power. By not upgrading them, you are limiting how much power you can make and where in the power range you can make it. Cylinder heads are typically costly in part cost and in labor to get done, which is why they are not a super common modification. However, they are one that can make a big difference.

1982-1995 5.0L Mustang with Aftermarket Cylinder Heads
1982-1995 5.0L with Aftermarket Cylinder Heads

How Will Upgrading My Mustang’s Camshafts Help the Exhaust?

Camshafts dictate the amount of air that enter and exit and engine, and when air can exit in terms of the overall timing. Are you starting to see a theme here? Swapping out the stock camshaft for an aftermarket one will allow you to improve the ignition/combustion cycle of the engine, feeding more air into the engine and allowing it to get out easier. 

Other Mustang Exhaust System Upgrades

Outside of the supporting mods that will help your engine to not only run more efficiently, but make more power, there are also a selection of other upgrades you can make that will just improve reliability or functionality.  There are quite a few exhaust accessories available for late model Mustangs that can include:

  • O2 Sensors (extensions and wires)
  • Over-axle pipes (the cat-back piping without the muffler/axle-back)
  • Exhaust tips (add-ons for the muffler, dress up part)
  • Exhaust heat wrapping (typically used on headers to keep engine bay temps down)
  • Catalytic converter delete pipes (removes the cats from the system)
  • High flow catalytic converters (adds cats to the exhaust system)
  • MIL Eliminator (removes the check engine light after removing the cats)
  • Exhaust hangers (replaces worn/rusted hangers and holds the exhaust in place)
  • Gaskets (to go in between the headers and the engine, making a tight seal)
  • Exhaust cutout systems (opens up the exhaust system before the mufflers, provides a loud tone)

Picking out different exhaust accessories is going to come down to your build and what it needs (and sometimes what you want).

Performance Camshafts Installed on a 2005-2010 Mustang GT
Camshafts Installed on a 2005-2010 GT

What is Exhaust Heat Wrap?

Most people try to cool down their engine by upgrading their radiators. Makes sense. However, there are other ways to augment cooling upgrades and take advantage of the heat.

  • Exhaust wrap insulates the exhaust pipes to keep heat in inside of dispersing into the engine bay
  • Soaking the wrap in water and then installing it allows the water to evaporate and tighten the wrap as it dries
  • Hotter exhaust gases allow for better scavenging for more clean air in the combustion chamber
  • Cooler intake chargers means denser air and more potential power

Exhaust heat wrap is a flexible material cut into strips used to insulate your exhaust system and trap heat inside the pipes. The heat wrap is made from materials like fiberglass or volcanic rock processed to withstand the extreme temperatures of your Mustang’s exhaust. To get the best performance out of your exhaust wrap, you should soak the wrap in water, then tightly wrap it around your exhaust, overlapping each pass slightly. By getting the wrap wet, you will be able to stretch it more as you wrap it. As the water evaporates out of the wrap, it will contract and give you a tighter wrap. You can also paint the wrap with high temperature paint to make it look better, but this is not necessary

Mustang Exhaust Heat Wrapping
Heat Wrap Roll

How Does Heat Wrapping Work?

Wrapping your exhaust will help increase the performance of your Mustang in several ways. The first is keeping your exhaust gasses hot. Heat always seems to be the enemy for the performance enthusiast, but a hotter exhaust allows for better cylinder scavenging. This means the hotter exhaust will move from the cylinder faster, allowing more clean air to come into your engine. This probably will not produce a difference you can feel, but a better flowing exhaust is always something you want to have. The second way exhaust wrap helps your Mustang is by reducing ambient heat. The exhaust generates a massive amount of heat, which in turn will saturate the engine bay with ambient heat. This heat will make its way into your air intake, intake manifold, fuel rails, and many other parts of your engine. By insulating the exhaust, you are able to reduce the ambient heat. This reduction in ambient heat will lower your fuel temperature and air intake temperature, resulting in a slight increase in power and efficiency. The cooler you can get your incoming air/fuel mixture, the denser it will be. The denser the mixture, the more you can fit into your cylinder which results in more power.

Heat Wrapped Foxbody V8 Mustang Headers

Is There a Downside to Wrapping My Exhaust?

Wrapping your exhaust is not a difficult task, but it can be time consuming to do properly. If you are installing a new set of long tube or shorty headers, wrapping your exhaust would be a great way to squeeze a little more power out of your new exhaust system. If you already have a set of long tube or shorty headers installed, the time and energy spent removing your exhaust and wrapping it would probably not be worth the slight gains you would see. You should also avoid wrapping your exhaust if you live in a very damp environment, or you drive the car in the winter where road salt is used. If you live in a damp climate, the wrap can trap moisture against your exhaust which can lead to premature failure. The same holds true for road salt, or other corrosive elements used in your area.

Heat Wrapped V6 Mustang Long Tube Headers

A Mustang's Catalytic Converters – The Basics

Catalytic converters have been equipped on all new cars in the United States since the 1975 model year to comply with U.S. Environmental Protection Agency regulations on automobile exhaust emissions. Their purpose is to convert the toxic byproducts of the internal combustion engine, exhaust gases, into less toxic substances by way of a catalyzed chemical reaction for release back into the atmosphere. Catalytic converters or “cats” look like small mufflers and are normally located directly after the exhaust manifolds (a.k.a. headers).

All new cars come with catalytic converters. The cats are located on the mid-pipe, and depending on the year of your Mustang you could have up to 4 cats. The more cats you have, the more restricted your exhaust flow will be. Aftermarket companies offer high flow catalytic converters for people who wish to increase their exhaust flow, while keeping their exhaust note more tame, and reducing the raw fuel smell typical of an off-road system. Most aftermarket cats will pass emissions testing. In California, you will want to make sure you have a CARB approved converter.

In the older days when converters were newer to the market, they did indeed rob cars of a good chunk of horsepower. However, in more modern times, they have become more efficient and hardly rob power in smaller HP circumstances (<500). The gains are minimal from removing and not truly needed unless you’re building a full out drag or race car. Much like a cold air intake, you might notice a bump in power, but don't expect a game changer.

Inside a Stock Mustang Catalytic Converter
Inside a Stock Catalytic Converter

Factory Catalytic Converters vs. High Flow Catalytic Converters

Factory catalytic converters have a very densely packed catalyst substrate to ensure that they are 50 state legal and that non-enthusiast drivers aren’t subjected to increased exhaust sounds and smells. The image above shows the inside of a stock cat. High flow cats dramatically increase the exhaust flow since their substrate is not as dense as the factory converter. Below is a shot inside a high flow cat.

Inside a High Flow Mustang Catalytic Converter
Inside a High Flow Catalytic Converter

Mustang Catted Mid-Pipes – Street Use

  • Convert toxic byproducts from the internal combustion engine into a less toxic substance
  • Required on street vehicles
  • Aftermarket catted mid-pipes increase horsepower and torque compared to restrictive stock factor cats

As you may have guessed by now, a catted mid-pipe is one that includes catalytic converters. These are ideal for use on street vehicles that require the use of catalytic converters by law; you will need to check your own local and state ordinances for exact regulations.

In general, most aftermarket catted mid-pipes feature high flow catalytic converters which provide a small bump in horsepower and torque over the restrictive stock factory cats, but they keep your Mustang emissions legal.

Mustang Off-Road Mid-Pipes – Track/Race Use

  • Off-road mid-pipes do not include catalytic converters
  • Without catalytic converters, your Mustang will produce more horsepower and torque
  • Malfunction Indicator Light Eliminator—MILs—can be purchased to turn off a faulty O2 sensor check engine light

Off-road mid-pipes do not include catalytic converters and are intended for off-road use only by the manufacturer. By removing the restrictive factory catalytic converters from the exhaust, your Mustang is able to produce more horsepower and torque, making such a mid-pipe perfect for race applications such as track and drag racing. 

With about two hours’ worth of work, you can replace the restrictive factory mid-pipe, with a free flowing off-road mid-pipe. Along with increased exhaust flow, you’ll get a more aggressive and louder sounding car. One thing to be aware of though, is that removing the cats will also result in a stronger exhaust smell, and the smell of unburned fuel which is removed by the cats. It is also illegal in all 50 states, so you run the risk of getting a fine if a law enforcement officer chooses to check for them.

1996-2004 Mustang BBK Off-Road Mid-Pipe
1996-2004 Off-Road Mid-Pipe

Which is Best for My Mustang?

In areas with emissions testing it is a good idea to keep your car catted. Not only does it mitigate the risk of getting a fine for improper equipment, it also makes your testing much easier because you don’t have to swap mid pipes or change tunes. Some people choose to run off-road for most of the year, then reinstall their catted pipe before testing. If you want more power for your car and you don’t live in a state with emissions testing, an off-road mid-pipe is one of the best mods you can do for your car.

What is a MIL Eliminator?

The factory calibration on your car is searching for a certain input from the downstream oxygen sensors placed in your cats. If it doesn’t get the proper readings from the O2 sensor, your car will throw a catalyst inefficiency code and illuminate the check engine light. To prevent the light from coming on, 1996-2004 Mustangs will either require a set of MIL Eliminators, or a tune with the rear O2 sensors shut off. MIL, which is short for Malfunction Indicator Light Eliminator, plugs in between the rear O2 sensor and the harness to block the codes generated by the rear O2 sensors. The MIL Eliminators will allow you to pass an OBD II inspection, but if you have visual or a sniffer, you will fail. If you have the rear O2s turned off in the tune, you will also fail as they will not read ready. If you have a 2005 or newer Mustang, you must have a tune to shut off the rear O2 sensors.

Mustang Malfunction Indicator Light Eliminator
MIL Eliminator Set
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