Exhaust is a part that removes the combustion gases from the engine and directs them outside via the tailpipes. An exhaust is a very crucial part of a car and has a significant impact on a car’s performance and fuel efficiency.
There are different types of exhaust systems available that the manufacturers use, and some aftermarket modifications can enhance the car’s sound and performance.
Let’s have a detailed look at two of the most common and popular types of exhaust systems currently in use, the downpipe, and cat-back exhaust systems. Which one is better, what are the different components, which produce better sound and more horsepower, and are they legal?
I have answered all these questions in this detailed comparison.
Cat-Back and Downpipe Systems
These are the two most commonly available and used exhaust systems in the auto industry. Where downpipe is unique only to turbocharged engines, the cat-back system is used in all cars. Both of these have their specific mechanisms and offer different benefits while having a few drawbacks as well.
A cat-back exhaust system can be judged by its name, it is essentially an assembly that starts from the outlet of the catalytic converter and ends at the muffler tip of the exhaust. It is a modification of the normal exhaust system and is available aftermarket.
A downpipe is found only in turbo engines, and it regulates the flow of exhaust gases from the turbine to the catalytic converter, to outside the car. There are two types, a catted-downpipe, and a catless-downpipe, depending on whether a catalytic converter is included in the assembly or not.
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Construction of a Cat-Back System
A cat-back system is made of high-strength material and starts from the outlet of the catalytic converter. It is connected via a hose to its outlet and extends to the tailpipe. It has different parts, including an oxygen sensor, a muffler, and a resonator, apart from the bolts and clamps that are used to hold the assembly together.
The cat-back system is a modification of the conventional exhaust system and its function is to enhance the flow of exhaust gases coming from the catalytic converter. Usually, the resonator is not removed by choice to further enhance the flow of gases and improve efficiency, as the gases get condensed in the resonator which can generate some backpressure.
Most of these exhaust systems are made of stainless steel or aluminum to offer high strength and corrosion-free operation.
Major parts include the exhaust pipe connected to a catalytic converter, an oxygen sensor, a resonator, a muffler, and tailpipes with a silencer.
Construction of a Downpipe System
In comparison, the downpipe is simpler in construction and has fewer components as compared to a cat-back system. It is a metal piping that regulates the exhaust gases flowing from the turbine and enhances their outflow to the catalytic converter.
The downpipe system is also made of stainless steel to bear extreme temperatures and is larger in diameter than OEM downpipes for better movement of gases.
The parts include the main metal tubing, engine mounting brackets, compression clamps, and a mandrel-bent. Catted-downpipe also comes with a high-flow catalytic converter.
Key Features Comparison
Both these systems have different mechanisms of functioning and also differ in their output, sound generation, costs, usage, and legality. It is important to contrast the main features of both the downpipe and cat-back systems to understand which one is better or best suited for which purpose.
| Comparison | Downpipe | Cat-back |
| Performance | Up to 40 hp gain | Max 10-15 hp gain |
| Sound (exhaust note) | Louder | Loud (resonator removed) |
| Price | Up to $600 | Can cost up to $2,000 |
| Emission | Unsafe (only catted is safe) | Safe |
| Legal | No | Mostly yes |
| Catalytic converter | Yes (catted) | Yes |
| Check engine light | Mostly Yes | Fewer Chances |
| Compatible system | Turbo-charged engines | Almost all types |
Installation Costs
Installation of both the downpipe and cat-back exhaust systems costs product price as well as labor charges. On the whole, a downpipe system is relatively cheaper to install as compared to a cat-back exhaust ($600 | $2,000).
Downpipe
Downpipe is a part of the exhaust system that exists only in turbocharged engines. It is a comparatively simpler piece of equipment, costs less, and can be installed/changed much more easily than a cat-back system. For this system, no major alteration is required in the exhaust system layout, and only the turbine outlet is linked to the downpipe, extending up to the catalytic converter.
Product cost: $300-400
Labor and services charges: $250
Cat-back
For cat-back installation, the whole exhaust assembly after the catalytic converter has to be altered. Most of the time, a larger diameter pipe has to be installed, along with the removal of the resonator. The exhaust tip or muffler is also modified for enhanced sound generation and performance.
Product cost: $200 – 300
Labor and services charges: up to $1,500
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Output Sounds
Both of these exhaust systems generate great, sporty sounds and offer a major upgrade. The catless downpipe generally produces a louder sound than the cat-back, but if the resonator is excluded, the latter can be very serious as well.
Downpipe
The downpipe uses larger diameter pipes, hence less obstruction to the flow of exhaust gases, even if a high flow catalytic converter is included in the circuit. On the other hand, the catless downpipe has no obstruction and produces a growling exhaust note.
Cat-back
Cat-back also uses a larger diameter pipe and produces good exhaust sound, but it is not as loud as a downpipe. Mainly because it starts at the end of the catalytic converter and has a regulated flow of exhaust gases. But if you remove the resonator and get a larger diameter muffler, it can also generate amazing exhaust notes.
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Power and Torque
Downpipe offers more increase in the horsepower as it enhances the functioning of the turbocharger, but the cat-back offers a more low-end torque by increasing the outflow of gases.
Downpipe
The downpipe regulates the exhaust gases in the turbine, enhancing the performance of the turbocharger, and offering more horsepower. But due to a catalytic converter, it has a slightly checked flow of gases so doesn’t offer much increase in torque.
Cat-back
A cat-back reduces the backpressure in the engine by removing the exhaust gases at a higher speed and ratio, so it immediately offers an increased torque at lower RPMs. The horsepower increase is not so substantial but can be regarded as merely 8-10%.
Compatible Systems
A cat-back can be considered a universal exhaust system, as it can be installed in any car. It is simply a modification of the regular exhaust, with a larger diameter pipe, louder muffler, and mostly an excluded resonator. A downpipe on the other hand is unique only to the engines with forced induction, particularly turbochargers. It regulates the exhaust gases in the turbine, which makes the turbo work better.
Regulations
There are strict regulations regarding any modifications in the exhaust systems, as these systems control the release of harmful gases and control emissions. A downpipe is illegal in the states with Cat-back can be installed under strict regulations.
Downpipe
A downpipe usually uses a less-restrictive (high flow) catalytic converter, and some don’t even use one (catless). This is highly dangerous and lets harmful emissions get released into the environment. For this reason, all the states have rendered the use of downpipes illegal, no matter which type.
Cat-back
A cat-back begins at the outlet of the catalytic converter and is generally considered safe, only if the cat is not altered and oxygen sensors remain intact.
You can pass an emission test with a cat-back exhaust but not a downpipe.
Pros and Cons of Cat-Back System
A cat-back system is a great way to boost your car’s performance, fuel economy, and sound, without compromising the warranty or failing the emission tests.
On the other hand, these are costly to install, can sometimes cause a rattling noise, and the resultant exhaust note may be too loud for some people.
Pros and Cons of Down Pipe System
A downpipe offers increased horsepower, louder exhaust notes, works with other modifications, and is cheaper to install.
Despite these benefits, it is illegal due to the release of harmful emissions, triggers the check engine light, voids your warranty, and can even cause some kind of smell in the car.
How to Choose the Best Exhaust System for Your Car?
You’ve to consider different things while buying an exhaust system so that you get the best one for your car. Let’s have a look at some of the criteria for selecting the best exhaust for your car;
1- Exhaust system type
There are different exhaust systems with different construction, such as cat-back, axle-back, and turbo-back systems. Select the one that’s most suitable for you, compatible with your engine, and offers better performance.
2- The car’s engine
Depending on the compression ratio, and induction type, different exhaust systems are suited for different engines. A downpipe is great for a turbocharged engine, while a cat-back is ideal for a naturally aspirated engine.
3- Material
Choose an exhaust system that’s made of highly durable material. Stainless steel is ideal for corrosion-free operations, while aluminum is lightweight and best for performance.
4- Requirement
Whether you’re looking to enhance the car’s performance or exhaust sound, you’ve to select the system wisely. A downpipe is great for enhanced output, while a cat-back offers better fuel efficiency.
5- Size
The diameter of the exhaust pipe defines its functions and is usually kept larger than the stock one. The ideal size of the exhaust pipe, that’s recommended by the experts, is 3”, ideal for both performance and fuel efficiency.
