Does aftermarket exhaust add horsepower?

By July 13, 2020October 18th, 2020Does It Add HP?, Performance Modification

Looking to install an aftermarket exhaust? They definitely look and sound cool – but do they add that horsepower?

To put it simply – yes. An aftermarket exhaust can provide additional horsepower to a car. They work by providing a better airflow for exhaust gases to escape the combustion chamber – providing more room for fresh air to enter and create a bigger combustion on the next cycle. 

Let’s get into more details on this aftermarket exhaust 🙂


  • An exhaust system allows exhaust gases to exit the combustion chamber – to make room for more air in the next combustion. 
  • An aftermarket exhaust increase horsepower by providing better airflow. Allowing the exhaust gases to leave quicker.
  • An aftermarket exhaust improves the sound of your car engine. If sound is the only thing you look for – get a cold air intake instead.
  • An aftermarket exhaust impacts different car models differently. Ensure to research for your car model and the exhaust of choice before purchasing.

What Does An Exhaust Do?

Your car engine delivers power  by mixing air and fuel in the combustion chamber to create combustion. The air is sucked from the surrounding, whilst the fuel is injected in. The injected amount depends on the amount of air that’s available in the combustion chamber. 

Once combustion happens, toxic exhaust gases are produced as by-products. These gases must be expelled from the combustion chamber as quickly as possible – to make room for fresh air in the next combustion. This is where an exhaust comes in. Exhaust gases are pushed into the exhaust system where they could flow out of the car.

An exhaust system typically consists of an exhaust header, a catalytic converter (CAT) and muffler. An exhaust header is the entry point to your exhaust. A catalytic converter converts the toxic exhaust gases into non-toxic ones such as carbon dioxide and water vapor. A muffler ensures that noise generated from the combustion is reduced as much as possible before they exit the car. 

Didn’t know your exhaust system is that busy did you? 😉 It gets even more complicated once we consider how extra horsepower can be tweaking the exhaust. Let’s carry on!

Imgae of catback car exhaust

How Can Aftermarket Exhaust Increase Horsepower?

The general way of increasing horsepower is to increase the amount of fresh air in the combustion chamber. More air creates more powerful combustion – delivering more power to your wheels. Every performance modifications like cold air intake and performance air filter aim to increase performance by increasing the available air in the combustion chamber. 

An aftermarket exhaust aims to increase horsepower with the same technique – increase the amount of air in the combustion chamber. Remember I said exhaust gases are produced after every combustion? The faster these exhaust gases leave the combustion chamber, the more fresh air can enter for the next combustion. 

To expel these exhaust gases quickly, we have to ensure there is a good air flow in the exhaust pipe. An aftermarket exhaust improves this airflow by doing below points: 


Decrease Exhaust Back Pressure

Back pressure is the air pressure that’s outside the combustion chamber. Back pressure must be kept low – so exhaust gases can be pushed out from the combustion chamber easily. Remember your high school physics – air particles will move from a high pressure area into a low pressure area. 

The easiest way to decrease this back pressure is to increase the diameter of the exhaust pipe. The wider it is, the more room it has to hold air particles – causing the air pressure outside the combustion chamber to decrease. Thus, allowing the exhaust gases to flow from the combustion chamber to the exhaust pipe quicker. Resulting in more room for fresh air to enter the combustion chamber for a more powerful upcoming combustion. 


Increase Exhaust Velocity

Exhaust velocity is how fast the exhaust gases can travel in the exhaust pipe to outside the car. Higher exhaust velocity means that exhaust gases can escape faster – allowing the combustion chamber to have more room for fresh air in the next combustion. 

To increase exhaust velocity, the exhaust pipe must be narrow. Too wide, and the exhaust gas will flow slowly. But wait… Didn’t I say  we need a wider exhaust pipe – so back pressure decreases and the exhaust gases can escape faster?

Well, that’s also true. That’s why this is a game of compromise. The diameter of exhaust pipe must be kept optimal. Not too wide and not too narrow. 

  • Exhaust pipe too wide – low exhaust velocity but also low back pressure.
  • Exhaust pipe too narrow – high exhaust velocity but also high back pressure
  • Balance must be achieved. 

Thankfully, a lot of aftermarket exhaust out there have taken care of this point already. 

Types of Aftermarket Exhaust

The types of aftermarket exhaust vary depending on the amount of components the aftermarket exhaust replaces. For example, a header-back exhaust replaces the entire exhaust system from the exhaust header all the way to the tailpipe (to the back).  I cover each of them in more detail below. 



As I mentioned, a header-back exhaust replaces the entire exhaust from exhaust header to the tailpipe. This means replacing the entire exhaust system in your car. Including catalytic converter and muffler. 

An aftermarket header-back exhaust allows you to have a larger diameter throughout the entire exhaust system. This provides more potential for performance but also most expensive and harder to install. 

Image of header back exhaust


Cat-back exhaust replaces the components of an exhaust system from the catalytic converter all the way back to your tailpipe. This is the most popular aftermarket exhaust. It’s cheaper than a header-back exhaust and can provide a comparable performance gain. A cat-back exhaust will replace the muffler. 

Image of Cat back exhaust


Axle-back exhaust replaces the components of an exhaust system from the rear axle all the way back to your tailpipe. This is the cheapest type of aftermarket exhaust and is the easiest to install. An axle-back essentially replaces the muffler in your exhaust but has lesser piping than a cat-back. 

Image of Axle Back Exhaust

Choosing an exhaust type mainly depends on your budget. Each exhaust system is great. It’s just a matter of how much are you willing to spend? 😉 If you are new, go ahead and look for an axle-back exhaust first.

Pros Of Aftermarket Exhaust

Improved Horsepower

An aftermarket exhaust has a wider piping. This provides better airflow – allowing the exhaust gases to easily escape from the combustion chamber which then provide more room for fresh air to enter. More air equals bigger combustion – which means more power delivered to your wheels!


Better Engine Sound

This depends on the driver and also the type of aftermarket exhaust you install. However, do expect a sound difference after you install an aftermarket exhaust. Some people dislike it, while others absolutely love it. I personally love the sound an aftermarket exhaust provides. They tend to growl louder – giving you that sporty feel. 

Be sure to check out the before and after sound of the aftermarket exhaust before purchasing it! Search for it on YouTube – type in the exhaust brand and also your car model. 


Aftermarket Exhaust Saves Lives!

Just kidding – but not really! Have you ever heard of the term “loud pipes save lives”? If you haven’t – the term indicates that a loud pipe will get you heard across the road. Other vehicles know you are coming, so they won’t run you over 😉 


Aftermarket Lasts a Long Time

Aftermarket exhaust is usually made of better materials than the stock exhaust. Stainless steel and aluminized steel being the most common. These materials lost a long time – and that’s why it’s common for manufacturers to provide lifetime warranty on these aftermarket exhaust. 

Featured image of a sports car with exhaust

Cons Of Aftermarket Exhaust

Can Be Expensive

An aftermarket exhaust can be expensive – depending on the type you purchase. If all you look for is an improved engine sound, then install a cold air intake instead. Aftermarket exhaust is a big piece of equipment that could be expensive to purchase and install. 



The sound changes from an aftermarket exhaust can be a pro or a con – this depends on you. I personally love the sound. Just ensure that you are not purchasing a straight pipe exhaust. The sound coming from a straight pipe exhaust can be deafening and straight up illegal. If you are wondering why people install this, check out this article where I discuss straight pipe exhaust. 

How Much Horsepower Does Aftermarket Exhaust Add? 

Honestly, an aftermarket exhaust will not provide THAT much horsepower. The stock exhaust system is already pretty decent in ensuring performance and comfort. An aftermarket exhaust will only provide significant horsepower if the stock exhaust is very restrictive. 

This might be the case on some cars – but not most of them. Ensure to research your car model’s impact on an aftermarket exhaust before purchasing one. Read the forums and find out what people are experiencing after they install an aftermarket exhaust on their cars. It is important to research specifically on your car model – different cars have different impacts.

Should I Install An Aftermarket Exhaust?

If you want to install an aftermarket exhaust just for the sake of performance gain – then I don’t suggest it. An aftermarket exhaust will not provide you with a significant performance gain. On average, you will see minor performance gain of about 2-5% increased in horsepower and acceleration.

However, if you want to install an aftermarket exhaust for all of it’s other pros like appearance and sound, then absolutely go for it! The sound difference it provides is significant – they sound much more powerful.

Here’s an article I wrote where I discuss what you should look for in an aftermarket exhaust and my recommendation.

If you just want the sound improvement, then I suggest you take a look at cold air intake instead. They are cheap and much easier to install. The sound improvement they provide is also significant. Check out this article where I discuss cold air intake.

Ifandi L.

Ifandi L.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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