Cat-Back vs Axle-Back ExhaustsLast Updated October 25, 2023 | Meghan Drummond
Exhaust upgrades are some of the first mods enthusiasts make to their rides. Of all the options out there, two of the most popular are cat-back and axle back exhaust systems. This guide will walk you through the differences between them so you can decide which is right for your vehicle.
What Is a Cat-Back Exhaust System?
Cat-Back exhaust systems replace everything from the catalytic converter back. That includes the mid-pipes, mufflers, and exhaust tips. Cat-back systems have an impact on sound, performance, and appearance. This trio of benefits makes it one of the most popular exhaust modifications.
- Deep Throaty Sound
- Horsepower Gains
- Easy Installation
- Most Popular Exhaust Mod
How Do Cat-Back Systems Work?
Cat-back systems typically use pipes with a larger diameter than stock exhaust pipes. This helps reduce backpressure, which can improve horsepower. The horsepower increase varies, depending on how restrictive the stock pipes were.
One feature you’ll notice on a lot of cat-back systems from high-end manufacturers like Roush, MBRP, and Ford Performance is “mandrel-bent” piping. Mandrel bending keeps the bends in a pipe from creating a pinch. This keeps the pipe’s diameter consistent and creates a deeper, throatier sound.
Are Cat-Back Exhausts Legal?
Because the catalytic converter is left intact, most cat-back systems are legal and emissions-compliant. Where some installers run into issues is with the decibel rating of their exhaust. Depending on local laws and statutes, there may be restrictions on how loud your exhaust can be. California is a famous example of this.
Cat-back systems are available with a wide variety of exhaust volumes and notes. That means many cat-back systems are 50-state legal.
Cat-Back Exhaust Sound
One part that most cat-back systems don’t come with is a resonator. Resonator deletes are a popular exhaust modification on their own. Though removing the resonator doesn’t make the exhaust louder, it does allow for further customization of the exhaust note. Removing the resonator also removes a lot of weight. The result is a lighter overall exhaust with a totally different sound. Many people describe the cat-back sound as deep and throaty.
Cat-Back Exhaust Sound Clip
Borla S-Type Cat-Back Exhaust on a 2015-2017 Mustang GT
What Is an Axle-Back Exhaust System?
Axle-back systems replace everything from the rear axle back. Axle-back systems typically include the muffler, exhaust tips, and sometimes a small section of piping. For vehicles that already have good intermediate and mid-pipes, axle-back kits provide improved sound at a much lower price than cat-backs.
- Rich, Deep Sound
- Wide Range of Looks
- Lower Cost
- Easier Install
How Do Axle-Back Systems Work?
Typically, axle-back systems don’t improve performance much, if at all. They do replace the muffler, which can free up airflow, but the gains are minor. Since they replace such a small section of your exhaust system, installation of an axle-back kit is usually very straightforward.
This isn’t always true though. For S550 Mustang owners, installing an axle-back requires cutting to remove the factory mufflers. Check out this axle-back S550 installation video to see what’s involved.
Flexibility for More Exhaust Mods
Another reason to get an axle-back over a cat-back is that it gives you the freedom to mix and match your exhaust system pieces. Cat-back systems come with a mid-pipe, but you might prefer to select your own. Considering the differences between X-, Y-, and H- pipes, this makes sense. Installing an axle-back and a mid-pipe is essentially building your own cat-back system. You just have more flexibility in what parts it’s made up of.
Axle-Back Exhaust Sound
High-quality axle-back exhaust systems also use mandrel-bent pipes. These pipes eliminate tinny notes and create a deep rumbling effect. Axle-backs usually sound richer and deeper than stock exhausts but don’t quite have the rumble of a cat-back.
Axle Back Exhaust Sound Clip
Borla S-Type Axle-Back Exhaust on a 2015-2017 Mustang GT
Is a Cat-Back or Axle-Back System Better?
It seems straightforward. While axle-back systems improve sound and looks, cat-backs do all that and improve performance. But that performance boost comes at a higher upfront cost. You can also pair mid-pipes with an axle-back later for the same performance boost and have more flexibility in what you choose.
The answer is that either exhaust system can be the best fit, depending on your build.
|Cat-Back Exhaust System
Slightly More Involved Install
|Axle-Back Exhaust System
Flexibility for Future Upgrades
|Little Performance Boost
Get an Axle-Back If…
If your primary concern is how your exhaust sounds, then an axle-back is a great choice. Axle-back installations are quick and easy, and they give you flexibility for future exhaust mods. This makes them a great choice if you’ve just started wrenching on your own.
Axle-back exhausts are also cheaper than cat-backs. Many of the same brands that make great cat-backs make equally great axle-backs.
If you want an inexpensive system that sounds and looks great, axle-backs are the way to go.
Get a Cat-Back If…
If you’re focused on finding a “one-and-done” exhaust system upgrade that improves sound, performance, and appearance, then a cat-back kit is your smartest choice. While you might save some money now with an axle-back, if you’re already planning more exhaust mods, doing them together will save you money and time. You’ll also know that the parts are compatible with each other.
What If You Can’t Decide Which System to Get?
If you’re still unsure which exhaust system is right for you, it never hurts to ask the audience. We surveyed our customers to find out which exhaust upgrade they’d go with, and a cat-back exhaust was the clear winner.
Cat-backs are the most popular exhaust mod for a reason. They offer a great trio of benefits and have a relatively easy installation and affordable price. The only challenging part will be choosing just the right system for your ride.
Be sure to check out our guides on the best cat-backs and axle-backs for an overview of features and differences.
Best Cat-Back and Axle-Back Exhausts
Searching for the best cat-back exhaust for your S550 can be exciting but challenging. With so many different products out there, it can be hard to find the best setup for you. Here’s a list of some of the best cat-back exhausts for 2015-2021 Mustangs divided up into several categories to help you find the best system for you.
A cat-back exhaust can give your S197 more power and a better sound. If you’re having trouble finding the best system for you, check out our list of the best cat-back exhausts for 2005-2014 Mustangs.
Is your Mustang’s exhaust too tame for your liking? If so, an axle-back exhaust can make your S550 sound as aggressive as it looks. Here are some of the top axle-backs for your 2015-2021 Mustang broken up into categories.
You don’t have to spend a lot of money to give your S197 a deeper, race-inspired sound. An axle-back exhaust can give your 2005-2014 Mustang a richer exhaust note without breaking the bank. Whether you’re searching for a raspier tone or pure volume, these axle-back exhausts both look and sound great.