What is a downpipe exhaust system?

Your vehicle’s engine produces harmful emissions that are dangerous to the environment. The purpose of the exhaust system is to convert these emissions into less harmful substances. It also involves transporting these emissions through the exhaust system and out of the tailpipe.

When referring to the downpipe, we mention a specific piece connecting the manifold and the catalytic converter. The manifold collects your engine’s gases, which then transports them into the rest of the exhaust system. In contrast, the catalytic converter produces these less harmful substances.


A downpipe exhaust is a type of exhaust that directs gases between the turbine house and the exhaust system.

Skunk2 Downpipe Highflow Cat For 18-22 Civic Type R

The purpose of a downpipe exhaust is to enable these substances to travel faster through the system without any restrictions. They are designed with large diameters to allow larger quantities to pass through. 

We did comprehensive research about the exhaust system and gathered the most important information we could find. Car enthusiasts from around the world gather online in themed forums to help those in need with specific information. 

This system is a complex one, but we got you covered. If you still have questions about this topic, continue reading as we explain the downpipe exhaust system in detail.

Table of Contents

What is a downpipe exhaust system?

The downpipe is an essential piece for your vehicle, and you should consider making this upgrade. It directs the gases from the engine directly into the exhaust system. That is why this piece is situated in the turbine housing and is an important piece responsible for increasing the system’s efficiency.

skunk2 downpipe

Catalytic converters clean exhaust gases right as they are produced. But these parts will also cause you to gradually lose power, which is the only downside of such a part. Car enthusiasts prefer to purchase and install an aftermarket downpipe if they want to push their vehicles to the limit. 

What does it do?

Whether you drive a Mustang or a BMW, the upgrade to a downpipe exhaust system is something worth considering. The companies producing these parts are considering every requirement their clients might have. That is why they also meet a stock vehicle’s performance requirements, making them highly versatile.

Environment protection is becoming increasingly important, so these downpipes also meet emission standards with a high air movement. The last step in upgrading your vehicle is unlocking more power by modifying the exhaust system. 

You must take advantage of the higher flow rates and install this upgrade. Make sure to check compatibility before purchasing and installing this part

Up-pipe vs. downpipe

Uppipe enables the exhaust gases to flow freely from the manifold into the turbo. In contrast, the downpipe will allow the gases to exit the turbo and enter the exhaust pipe. These parts are easy to understand as they have opposite functions.

You will have to choose the ideal one for your needs. The up-pipe will offer a more aggressive feel while also reducing response time. It will give you a boost in horsepower and will help you reach higher performances with your car.

The downpipe provides as much as 25 horsepower without a tune, so you should choose this option if you want raw power and better performance in a specific way. 

Pros & Cons

Installing a downpipe on your vehicle comes with several pros and cons. Take a look at these points and decide if installing it is worth it. 


Increased horsepower – you can gain up to 40 horsepower with a catted downpipe if you also tune your vehicle. It is a significant boost that will provide a significant advantage in racing.

  • A 180 HP car can get up to 220.
  • A 200 HP car can get up to 240.
  • A 250 HP car cat get up to 290.

Louder exhaust sound: Because the downpipe is wide to allow more air to pass through, it also allows sound waves to travel better. It results in a louder sound when you accelerate.

High versatility: A stock downpipe can be very restrictive if you plan to upgrade your car. But if you replace this part, you have more freedom to work around your car and gain more performance.

Cheap price: a high-quality piece costs around $350, which is a low price considering the significant horsepower upgrade. The performance increase in a Civic Type R or a Ford Focus ST is massive. However, the price tag does not include the installation and labor work. 


Bad exhaust smell – because the catalytic converter is less restrictive, you might experience an unpleasant smell after installing the downpipe. This smell is only noticeable when you are stopped for a long time, such as in heavy traffic.

Void warranty – you are installing an aftermarket mod, which might void the car warranty. But this will only impact the turbo and exhaust system parts. You might be able to keep the warranty for electronics and other systems.

Street illegal – these parts are not legal for public roads. Still, a catted downpipe might be harder to differentiate from stock ones. In general, they are intended for legal racing and off-road courses. 

Different types

There are six different types, and it is important to know which one is the best for you. A Volkswagen mk7 GTI will use a different type of downpipe than a Subaru WRX.

  • Flange with simple pipe
  • Bellmouth
  • Split bellmouth
  • Divorce wastegate
  • Cast outlets
  • Formed piping

Flange with simple pipe

This type has a major advantage due to its simple design and relatively cheap cost. It is easy to form, and the pipe requires little manual work. It is one of the main reasons why factories prioritize this type. 


Like the previous type, the Bellmouth is easy to manufacture and packages easily. It lacks complexity, and therefore the risk of failure is minimal. Car enthusiasts favor the Bellmouth the most, giving the biggest performance improvement.

Split Bellmouth

This option is split because it separates the gasses in the beginning and joins them together at the rear of the bell mouth section. There are various advantages to such a system, including the reduced cost and simplicity. Keeping things simple will always get you the best results.

Divorced Wastegate

To combine several advantages, the gasses are kept away from the turbo outlet until they reach the end of the system. When they are combined in the back, the process is more efficient. There is also a significant pollution reduction. 

Cast outlets

This design allows for the heat to be kept in the exhaust. It is also easy to design, and you can make it in any shape you want. The disadvantage is represented by increased weight and cost. 

These pieces will have a significant weight which will negatively affect the performance. Some manufacturers will sell this piece at an increased cost because the casting forms are very expensive and can be quite complex.

Formed Piping

This part shares the same freedom in design with the casting, but it is also cheaper and lighter. The manufacturer has to be precise with the building process as improper forming will negatively affect the flow. If this part has a poor design, then the flow will struggle regardless of the quality of the entire system.

A catalytic converter is good for the environment and will prevent this problem from happening. The diameter of the pipe has a small effect on the flow rate, but it is not an important factor. If your vehicle has 300 horsepower, a pipe 2.5 inches in diameter will be just enough. 

3 inches are recommended for faster vehicles that can deliver 600 horsepower. Beyond this point, several restrictions come into place.  


Mk7 GTi Catted Downpipe

The catted downpipe is better for you if you are driving on the street with a daily driver. While they provide 10 less horsepower than a catless ones, they feature more advantages. It includes fewer emissions and the absence of a specific unpleasant smell.

Catted downpipes are installed with a catalytic converter that cleans the gases. However, you won’t find this part in a catless downpipe where the fumes gain an unpleasant odor. 

Pick a catted downpipe if you have an Audi A3 or a similar vehicle that you drive daily to work. It increases efficiency and reducing emissions. The name of this part implies that it contains a catalytic converter, which is also the most expensive part of your vehicle. 

This catalytic converter is often manufactured with precious metals, therefore increasing its price and value. If you need to replace a catted downpipe, you should expect to pay more. 

How many HP does it add?

Installing a downpipe might be a great idea if you want to gain more horsepower. Without a tune, you can expect to get 20 extra horsepower to your engine. If you also tune your car, the horsepower gain increases significantly. It happens because the exhaust flow in your vehicle is exponentially increased.

On turbocharged cars, the upgraded downpipes will greatly increase horsepower and torque. With the necessary software, they can provide exceptional performance and make a vehicle more engaging and responsive. 

Here’s a list of the biggest manufacturers out there.

Milltek SportDerbyshire, UK
InvidiaOsaka, Japan
Cobb TuningAustin, Texas, USA
HKSTokyo, Japan
Agency PowerPhoenix, Arizona, USA
GReddyOsaka, Japan
AWE TuningHorsham, Pennsylvania, USA
Tial SportPompano Beach, Florida, USA
TomeiYokohama, Japan
ETSHaltom City, Texas, USA

Downpipe vs. Catback

Catback is a collection that includes pipes, the resonator, and the muffler from the catalytic converter. It differs from the downpipe, which extends from the exhaust manifold to the front of the converter. 

Depending on the manifold you already have, you can find single downpipes or dual ones. Experts in the automotive industry mutually agree that a dual system is always better than a single one. 

The catback system will increase the horsepower in your vehicle while also reducing harmful emissions. It is a balanced choice that most people make due to its versatility. 

Catted vs. catless

APR Catless downpipe

You might wonder which one is better, the catted or the catless downpipe. The answer is yours, where you decide which is most ideal for you. Take a look below, where we explore the differences between these parts.

EmissionWorse than stockWill probably fail emissions tests
Catalytic converterComes with a catalytic converter that is less restrictive.Does not have a catalytic converter.
HPImprovementEven more than catted
Soundmore aggressive than the stock option.more aggressive than the stock option.


A catted downpipe will always have worse emissions than the stock one, but it is superior to the catless one. You should always consider that this part of your area’s regulations requires fewer emissions.

But the catless downpipe is also worth considering if you have no limits. It has horrible emissions and will most likely fall all the emissions tests. 

Catalytic converter

A catted downpipe comes with a catalytic converter included, which is less restrictive than the stock one. The flow is improved, and emissions are being controlled thanks to this additional part.

Catless downpipes do not feature this expensive part. While the maximum exhaust flow is ensured, the emissions are way beyond the usual limit for stock vehicles. 


Suppose you want a significant upgrade while also keeping the environment clean. In that case, the catted downpipe can meet both requirements. You will notice a decent improvement in performance.

Catless downpipes provide more horsepower, which is a significant upgrade for the performance. Those who value performance the most always go with this option.

Sound improvement

Both of these parts will provide exceptional sound improvement. You can enjoy a more aggressive sound from your car regardless if the downpipe installed is catted or catless. 

Installation cost

Separately, a downpipe can sell for as low as $80, but it can reach higher prices up to $600. The cost will be directly influenced by the materials used and the manufacturer that is selling them. The catless downpipes will sell for around $100, but you also have to consider the installation cost. 

But if you value quality the most, you might want to filter the cheap ones and only look for downpipes that have been manufactured with good materials by a trusted producer. Those can sell for up to $500, but the value is exceptional. 

Luxury cars will have better parts. For the installation of a downpipe exhaust, you will have to pay more than $500, especially if the brand is well known. However, the local auto repair shop might help you with a custom offer from $200 to $400. 

Have you found out if you’re getting one from either of these companies?

Catless downpipe
  • Invidia
  • Cobb Tuning
  • HKS

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