What is a Downpipe and What Does it Do?

Do you have a car? Do you understand how it works? Not the Accelerator Brake Clutch (ABC), I mean, what goes on under the hood? I'd wager most of you don't know.

Most people love driving high-performance cars and getting them tweaked by others. Not all car enthusiasts are technical geniuses or skilled mechanics. Though you are no technical genius, you have probably heard of things like turbos, superchargers, and downpipes.

These are components mostly used in high-performance cars. Of all the components, perhaps the most discussed component is the downpipe. Well, there is a reason why the downpipe forms such an integral part of the car's exhaust system.

Today, this article is going to discuss all the relevant information regarding downpipes.

What is a Downpipe?

A downpipe is simply a pipe that is located at the front of the exhaust assembly. It connects the engine to the main exhaust system. But, unlike the other regular pipes, this one is specially designed for turbocharged engines.

You won’t find this pipe in normal cars. It is often installed as an aftermarket component in place of a restrictive factory component. Its primary function is to efficiently channel exhaust gases away from the turbocharger's turbine housing.

What Does a Downpipe Do?

A turbocharger is a powerful engine that produces a lot of exhaust gas. A normal pipeline can’t handle the excessive heat and the amount of gas produced by a turbocharger engine.

A downpipe is designed in such a way that it channels high-pressure exhaust quickly without interruption while still harnessing the energy. With no restriction in the exhaust path, the turbocharger will spin more freely, improving response time and power delivery.

Most cars straight from the showroom floor come with an OEM (Original Equipment Manufacturer). This OEM complies with emission rules and other vehicle standards, making the cars inherently restrictive. Meaning the car won’t give top performance even if the engine is capable of‌ it.

And how do they do‌ it? By including a catalytic converter to the exhaust pipe. While catalytic converters play a crucial role in reducing harmful emissions, ‌it also obstruct exhaust flow. These obstructions slow down the turbo, leading to delays in power delivery.

Aftermarket downpipes, on the other hand, usually carry high-flow catalytic converters or are designed to operate without them. You can get the one that will fit your car type and performance needs.

Benefits of Upgrading Your Downpipe

The first step to improving vehicle performance is often ECU tuning. The next step is upgrading the downpipe. That is what you get when you upgrade the pipes.

• More Horsepower - The bending structure of most high-performance downpipes is optimized to minimize turbulence and allow more gas to flow freely. This enables your engine to breathe easier and thus produce more power.

• Improved Flow - The diameter of the after-market downpipes is bigger when compared to the stock. This wider pathway improves the flow of the exhaust, hence giving a smoother, more efficient running engine. This change also aids in the reduction of turbo lag, defined as the time between when the accelerator is pressed and the spinning up of the turbocharger.

• Better sound - Generally speaking, a high-performance downpipe will significantly enhance the exhaust sound of your car.

• High-quality material - These downpipes are usually made from high-quality materials, such as stainless steel, which can bear very high temperatures, hence being solid and durable.

Types of Downpipes Explained

Every part of an exhaust system including the downpipe comes in various designs to meet different performance needs and vehicle setups. Here are some of the most popular ones.

Flange with Simple Pipe

Similar to the name, this downpipe features a flange welded to a straight pipe. This is one of the most popular pipes as it is more affordable and easy to install than other designs. However, its simplicity sometimes can limit ‌exhaust flow efficiency in high-performance applications.

Bellmouth

If you’re looking for maximum performance without extensive modifications this downpipe is for you. This one has a wide bell opening at the end. The design helps to flow exhaust gases freely reducing turbulence and backpressure.

Split Bellmouth

This one is similar to the bellmouth downpipe, except they have two openings divided by a divider in the center. The best part about this pipe is you can adjust the divider to separate the turbine and wastegate exhaust paths into individual channels.

Divorced Wastegate

You could say this one is an upgraded version of the split bellmouth. This downpipe features two openings that keep the gases entirely isolated until they exit the downpipe. This reduces back pressure and improves throttle response.

Now, the design is one part of the puzzle. The material used for making the downpipe also plays an equal role in performance, durability, and weight. The two most popular options include Castings and Formed Piping.

Castings give manufacturers more options for designing complex downpipes. They are also usually very strong and resistant to heat and stress. The only problem is castings are heavier than formed pipes and the casting process is expensive.

On the other hand, the forming process of formed pipes is generally cost-efficient and easy. They are also lighter than casts. The drawback is they don’t come in the desired shape as they have limited design flexibility and are more susceptible to warping at high temperatures.  

Cat vs. Catless Downpipes

A catalytic converter is a device that helps to control exhaust pollution. Most cars you see on the road today have at least one converter; some cars have two.

There are some precious metals inside the catalyst, usually platinum, palladium, or rhodium. When the harmful emissions of carbon monoxide, nitrogen oxides, and hydrocarbons pass through the converter, the metal inside initiates a chemical reaction and converts it to carbon dioxide, water vapor, and nitrogen.

Now that you know the functions of a catalytic converter which downpipe will you choose? Well, whether you pick a converter or a downpipe without one, it’s about balancing better performance with being good for the environment or the other way around.

If you go for ‌catless downpipes, you get unrestricted exhaust flow which leads to more power and performance. However, car components like this are illegal in most parts of the world. On the other hand, opting for a cat downpipe slightly restricts exhaust flow and can lead to minor losses in power and torque.

One best things you can do is install a catted downpipe that uses high-flow catalytic converters. This way you get better performance without breaking the rules.

Legality of Catless Downpipes

I would recommend a downpipe cat - simply because not all places allow downpipes without cats. If you remove the converters in the States, the EPA will slap you with big fines. Depending on where you are in Europe, removing the catalytic converter can even land you in jail.

But how do they know that you removed the catalytic converter? Most countries require you to get regular emission tests and other inspections. If you don't have a converter, you will most likely fail the test.

How Much Horsepower Does a Downpipe Add?

Of course, it is quite obvious that a downpipe raises horsepower, but one of the most common questions is how much horsepower it raises. While there is no exact answer to this, since ‌horsepower gain can vary depending on engine type, tuning, and turbocharger size.

For example, a larger turbocharger permits more airflow than a smaller turbocharger, thus adding more horsepower.

Speaking of average, a well-designed downpipe can add anywhere from 10 to 25 horsepower. Beyond the downpipe, one could have ECU tuning, intake upgrades, and intercooler and exhaust upgrades.

Will a Downpipe Make My Car Louder?

Yes, an aftermarket downpipe will make the exhaust louder, especially a catless one. Most car enthusiasts love louder, deeper, more aggressive sounds, so if you are one of those, with the following upgrade, you will just fall in love.

A catted downpipe would be ideal for people that love quiet rides or just do not want to disturb the neighbor. Another thing to note is that not all cars will produce the same sound even if the cars have the same downpipe. The sound can vary depending on exhaust setup, muffler choice, and additional resonators.

Should You Buy a Downpipe?

The answer is no if you own a normally aspirated car. Why is that?  Its because downpipes will not fit onto your car's exhaust system. If you own a turbocharged car, you still need to think twice because your car may or may not benefit from the upgrade.

If you own a new model turbocharged car, then the installation of a downpipe is not the right upgrade because most of the latest models come up with higher power and performance.

Whereas if you own an old model turbocharged car, or want to take your sports car to the racing ground, a new downpipe can improve your HP.

Also, keep in mind that the standard downpipe for sports cars is typically of excellent quality. It’s entirely your prerogative whether you’re satisfied with your exhaust materials or want to modify them further to get that extra boost.