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Aftermarket exhaust: How does it improve car performance?

No car is made perfect, specifically when it comes to exhaust systems. A popular car model from a well-recognised company may give a safe and functional ride, but this doesn’t necessarily mean it fully optimises its exhaust system.

An aftermarket exhaust is recommended to get the most power out of a vehicle. Installing it improves airflow inside a car’s exhaust system, allowing the engine to perform at its peak. It’s one of the best ways to improve engine performance and ensure fuel economy. 

This article is a beginner guide to aftermarket exhaust and its part on improved car performance. Read on to know more. 

What does stock exhaust do?

The stock exhaust is the original exhaust system installed on a vehicle from the factory. It mainly balances a car’s performance, efficiency, and noise reduction. While it doesn’t give the aggressive exhaust notes many car enthusiasts seek, it’s sufficient for most drivers.

It mainly consists of the following components: 

  1. A combustion chamber – where combustion takes place
  2. An exhaust manifold/header – the entry point of the system
  3. A catalytic (aka CAT) converter – turns exhaust gases non-toxic
  4. Pipes – where route air out
  5. A resonator – rejects sound waves, allowing the muffler to reduce noises 
  6. A muffler – redirects airflow to eliminate combustion-generated noises.

What happens inside an exhaust system?

A car engine delivers power through combustion. Combustion takes place when the petrol is mixed with oxygen in a combustion chamber. Its mixture is then ignited in the chamber, producing energy and forces used to drive the engine.

Combustion produces toxic exhaust gases as by-products. They must be immediately removed from the combustion chamber to allow more room for fresh air to enter for the subsequent combustion. The CAT helps turn toxic exhaust gases, specifically carbon dioxide, into non-toxic. They’re then routed out through the pipes. 

Combustion also makes a lot of noise. The muffler reduces this noise in the exhaust system by restricting exhaust gases while ensuring they can move quickly out of the tailpipe. Resisting the desired flow of fluid through pipes causes back pressure

Back pressure ensures optimal air-fuel-ratio, but it robs power. This causes the engine to utilise its generated power to force the exhaust gases out of the tailpipe instead of using it to run the car, consequently slowing down its optimal performance.

How does an aftermarket exhaust improve car performance?

Increasing the amount of fresh air in the combustion chamber is the key to improving a car’s power. This is what exactly an aftermarket exhaust system is made of. Specifically, it improves airflow in the engine in two ways: 

  1. Decrease the back pressure 
  2. Increase exhaust velocity

Decrease back pressure

In addition to what’s mentioned earlier, back pressure is the air pressure outside the combustion chamber. It must be kept low or, ideally, totally eliminated so exhaust gases can easily flow out from the combustion chamber. 

This is where aftermarket exhaust comes into play. Widening the diameter of an exhaust pipe, instead of relying on the stock exhaust, is an excellent way to reduce back pressure. The wider it is, the bigger the room for more air particles.

When the engine has good airflow, the air pressure outside the combustion chamber is reduced, and exhaust gases can easily flow out. When this happens, there’ll be more room for a new set of fresh air, resulting in more powerful combustion. 

Increase exhaust velocity

Exhaust velocity is how fast exhaust gases leave the engine through exhaust pipes. The higher the exhaust velocity, the more exhaust gases escape, resulting in an improved airflow for the next combustion. 

The catch is to increase exhaust velocity, a “narrow” exhaust pipe is needed, which contradicts the suggested wider exhaust pipe for reduced back pressure. However, both are necessary. 

What to look for is an exhaust pipe that’s not too wide or too narrow. Most companies are aware of this, so they’ll help find the suitable diameter and the ideal aftermarket exhaust system for a car. 

How much does an aftermarket exhaust system cost?

The cost of replacing, building, and installing a custom exhaust system in the UK is between £300 and £1,500. Note that this is for the parts and the labour involved. The cost varies, depending on the car model and the preferred garage.  

Can an aftermarket exhaust system be financed?

In terms of financing, many aftermarket exhaust manufacturers and other third parties finance the installation of aftermarket exhausts in the UK. They typically offer 10-30% APR deals for 6, 9 and 12 months.  

The only downside is that they must run a credit check first per the UK’s Financial Conduct Authority (FCA) regulations. If you have a bad credit score, it’s recommended to improve it first. 

Consider looking for alternative financing. Take CreditNinja installment loans in the United States, for example. They’re often unsecured, have flexible repayment options, and are more lenient towards borrowers with bad credit.  

Bad credit and payday loans for up to £2,500 are available in the UK. Shop around and compare different offers. Opt for fair, precise, transparent, and favourable repayment terms that’ll make the instalments affordable. 

Is aftermarket exhaust system legal in the UK?

Installing an aftermarket exhaust system is legal in the UK as long as the modification doesn’t make the car louder than its type approval allows. Modifying a car that has been financed is totally legal as well. 

The laws related to this are complicated as they depend on a vehicle category, so it’s better to seek legal advice. It also pays to read your loan paperwork carefully and reach out to your lienholder before making any changes to the car. 


Ignorance could result in the opposite of what’s expected from an exhaust modification. Be familiar with your car model and the installation of an aftermarket exhaust system first to make an informed decision. If unsure, it’s always recommended to tap a professional.