How do exhaust systems work?

When you turn the key and start your car, you may not think much about the exhaust system and how it works. After all, it's out of sight and out of mind, hidden beneath your vehicle, or hanging around below the rear bumper. But the exhaust system is a crucial component of any car, responsible for the disposal of harmful emissions and ensuring that your car runs smoothly. In this article, we'll take a closer look at how car exhaust systems work, from exhaust manifolds to catalytic converters, centre silencers, and rear mufflers.

The exhaust manifold or header is the first component of the exhaust system and is responsible for collecting the exhaust gases from the engine's cylinders and directing them into the exhaust system. The exhaust manifold is typically made of cast iron or stainless steel for many performance engines. It is from the exhaust manifold that a turbocharger may be fitted, but that's another story. 

The exhaust manifold is connected to each cylinder of the engine with a flange and a suitable exhaust gasket. In the case of a flat 4 or flat 6 engine, or even an engine with a Vee configuration, the manifold is likely to be in more than one piece or side. The ideal engineering solution is that each cylinder has a pipe the same length as the other cylinders before they all meet together, or at least join the others from their side in what is known as a collector. 

It is from this collector that a front-engined vehicle would have an exhaust downpipe fitted, or in the example of an aircooled VW or Porsche, a rear silencer would be attached. 

If you own a more modern vehicle (mid-nineties onwards) or an older classic imported from California, you are likely to have a catalytic converter fitted as standard. 

The catalytic converter is responsible for reducing harmful emissions, such as carbon monoxide, hydrocarbons, and nitrogen oxides, that are produced by the engine. It does this by using a catalyst, usually made of precious metals like platinum, palladium, and rhodium, to convert the harmful emissions into less harmful substances, such as carbon dioxide, water, and nitrogen. The catalyst is coated onto a ceramic honeycomb structure, which provides a large surface area for the chemical reactions to occur.

The catalytic converter is usually located close to the engine, and it's connected to the exhaust manifold by a pipe. As the exhaust gases pass through the catalytic converter, they come into contact with the catalyst, which causes the chemical reactions to occur. The catalytic converter can reduce harmful emissions by up to 90%, making it an essential component of any modern car.

Sadly, because of the precious metals used inside catalytic converters, they are often targeted by thieves, even when fitted to the vehicle.  

Whilst catalytic converters are great for the environment, those looking for better performance prefer to operate without them. If you have a vehicle that has a catalytic converter fitted you may opt to fit a cat bypass pipe. This involves removing the catalyst and replacing it with a piece of unsilenced pipe, the same shape, length, and diameter instead. It is worth noting, this could cause you problems if your vehicle ECU is relying on a sensor reading from the catalyst, or of the emissions after it. Likewise, the legality of such a modification is questionable and could cause your vehicle to fail its annual inspection. Do your research on this, before you buy.

Another option, and one which shouldn't catch you out with legislation, is fitting a sports catalytic converter. This still offers some emission reduction properties but instead of having 400 cells per square inch, each with high-value metals within it to oxidize the gases, the sports cat might have 200, or 100 cells per square inch, allowing the waste gasses to flow far more freely to the tailpipes. This in turn releases more power from the engine. 

After the catalytic converter, the exhaust gases (in a front-engined vehicle) pass through a centre silencer, sometimes known as a resonator. This silencer is designed to reduce noise and vibration from the exhaust system, and it's usually located in the middle of the exhaust system - probably under the seating area in your car. 

The center silencer is made up of a series of chambers and pipes, which are designed to reflect and absorb sound waves. As the exhaust gases pass through the centre silencer, they are forced to change direction several times, which reduces the intensity of the sound waves, and the noise that is created. 

Tuning companies can engineer these silencers to help produce different engine notes and engine responses. As with the sports cat, the less obstruction for the spent gasses the better the performance. 

The final component of the exhaust system is the rear muffler, also known as the rear silencer or back box. The rear silencer is responsible for further reducing noise from the exhaust system, and it's usually located at the rear of the car.

Just like the centre silencer, these contain a series of chambers and baffles, designed to reflect and absorb sound waves. 

Your exhaust back box also plays an important role in maintaining back pressure in the exhaust system. Back pressure is the resistance that the exhaust system provides to the flow of exhaust gases, and it's essential for maintaining engine performance. The rear muffler is designed to provide the correct amount of back pressure for the engine, which helps to optimise performance and fuel efficiency.

As the name suggests, these are systems that have no additional silencers fitted in place and it is only the size, shape, and length of the tubing which will affect the noise and performance of the engine. This type of system can often be found on Beach Buggies, for example, the EMPI Dual Cannons. It is also a popular option on classic Porsche race cars. In some instances, an additional exhaust baffle can be inserted inside these pipes to help control noise, or a bolt-on 'Spark Arrestor' can be slotted over the end to offer a little extra sound deadening if required. 

In conclusion, the exhaust system is a crucial component of any car, responsible for reducing harmful emissions and ensuring that your car runs smoothly. The good news is, if you don't like what you have fitted, either from an aesthetic point of view, or from the way it sounds, something can be done about it. We stock a great range of sports and performance exhausts for VW and Porsche. 

Equally, if your pipework has gone all rusty, we could help you with a shiny stainless steel exhaust that will last a lifetime and add to the vehicle's value, not to mention save you cash in the long term. 

Drop our tech team an email if you'd like to know more: help@heritagepartscentre.com 

Andy