In petrol and diesel motoring, there are two certainties that drivers accept: cars produce both fumes and noise. This is inescapable, after all. Power is delivered to our cars using various pistons, fuel and chemical reactions. This process generates a lot of waste energy, which is typically manifested through smoke and heat.

Once this waste is created, it needs to go somewhere. This is where the exhaust comes in. Aside from this, you may still be asking yourself “How does the exhaust system work?” If you’re still a little foggy on your exhaust, keep reading as we explain the inner workings of this complex piece of machinery.

What does an exhaust do?

The exhaust system in your car has four main responsibilities:

1. Noise control

Cars make lots of noises. From grinding gears to fans in engine bays, there’s a lot of noise pollution going on in our motors. One of the main functions of the exhaust system is to mute some of this noise. You can think of the exhaust as one continuous tunnel pointing from the front to the back of your car. As a result, the exhaust absorbs essentially all the vibrations and rumblings of your engine bay.

Car noise is under strict legislation in the UK. Specifically, exhaust tips on small-medium cars must not exceed 80dB. Larger cars like pickups and vans, however, have a limit of 89dB. This is to accommodate for the additional noise generated by typically larger engines with bigger parts.

2. Waste gas dispersion

The main functionality of the exhaust is to transport waste gases from one point to another. Acting as a complex funnel, the exhaust carries leftover fumes from your car’s combustion process, re-distributing them throughout the exhaust and surrounding environment. Two main parts of the exhaust are at play here: the exhaust manifold and the catalytic converter.

The exhaust manifold is directly attached to the engine block and helps suck down excess fumes towards the catalytic converter, which sits between the manifold and the end of the exhaust. The catalytic converter then utilises a catalyst to convert harmful fumes into safer, environmentally friendly alternatives such as steam.

You can learn more about catalytic converters in our blog: Catalytic converter theft: why it's on the rise and how to prevent it.

3. Performance improvements

Generally, the fewer pollutants that your engine is left to deal with, the more space it has to draw in clean air that it can convert into power. The more efficient your exhaust, the better it is at pulling away harmful fumes.

4. Improving fuel economy

While greater fuel economy isn’t the main intention of your exhaust, there can be some nominal benefits of fitting an aftermarket model.

This is because stock exhausts tend to be quite narrow and restrictive. Models produced by third party manufacturers are therefore wider. This allows them to draw in more waste fumes, which means the engine won’t need to work as hard to draw fuel and generate power.

Most modern cars have exhausts that are already heavily optimised, so you’re unlikely to see many fuel economy or performance benefits by changing. However, cars produced around 30 years ago, many of which are still in circulation, could see benefits ranging from 2%-10% more efficiency.

Exhaust system diagram

For a more visual representation, we’ve created a diagram showcasing where each part of the exhaust sits:

Let’s look at the function of each piece:

  • Exhaust Manifold: Attaches directly to the engine and draws down waste fumes toward the catalytic converter.
  • Exhaust Pipe: Continues the flow of fumes toward the catalytic converter and silencer.
  • Catalytic Converter: Takes in waste fumes and transforms them into cleaner, environmentally friendly fumes.
  • Silencer (Muffler): Primarily used to dampen engine noises by absorbing vibrations.
  • Tailpipe: Helps release exhaust fumes generated by the catalytic converter into the environment. Larger tips produce more aggressive sounding exhaust noises, while not affecting performance in any discernible way.

How does an exhaust silencer work?

While exhausts have a naturally dampening effect on engine noises, sometimes, additional help is needed to keep levels within legal limits. This is where silencers come in.

Also called Mufflers, silencers are attached at the end of the exhaust system. They are essentially sound absorption chambers that seek to reduce the amount of vibrations from the engine and flow of gases.

Find fuel efficient cars today

If you’re on the hunt for a car that’s both fuel efficient, quiet in operation and fits your needs, you’ve come to the right place. At, you can find all sorts of used cars in a variety of sizes. From larger pickups with larger exhausts, to city cars with relatively small systems, we’ve got you covered.

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