The Exhaust System
The Exhaust And Its Components Explained
In this article, we at Steves Auto Clinic, leader in the field of vehicle repairs, maintenance and servicing, will enlighten you about the exhaust system. You may (or may not) think that the exhaust is simply a piece of piping, but we can assure you, it is so much more than that. We will introduce you to the specific functioning of the exhaust, to the most commonly used exhaust system terminologies, to the different types of exhausts used on vehicles, and to how you can maintain your vehicle’s exhaust. Let us then start by looking at the working and purpose of the exhaust.
Working & Purpose
The exhaust system extends from the engine manifold in the front to the rear or sides of the vehicle. It works in the following manner. The exhaust manifold or headers, connect to the cylinder head. Here toxic exhaust gases, such as hydrocarbons, carbon monoxide and nitrogen oxides, are pushed out of the engine by way of one or more pipes. These gases then flow through the exhaust system and on its way out, they are analysed by an oxygen sensor, refined by a catalytic converter and any excessive sound is quieted down by way of a silencer/muffler. By the time the gases leave the vehicle through the tailpipe, the system has made the vehicle to run smoother (more efficient), quieter (less noise pollution) and cleaner (less air pollution). It is worthy to mention that exhaust emissions from the engine of every vehicle (light and heavy, passenger and commercial) must comply with applicable regulations promulgated under the Atmospheric Pollution Prevention Act, 1965 (Act 45 of 1965). This is important to keep in mind when we discuss the catalytic converter, but let us not jump ahead of ourselves. This then, are the primary function of the exhaust system – to remove waste gasses, make the vehicle more efficient, and reducing noise as well as air pollution. There are however many components and exhaust type-references that may be unfamiliar to you as a vehicle owner or even a prospectus owner. Let us have a look at them.
When discussing a system such as the exhaust system, we readily use words that may not be familiar to everybody. To see to it that this is not the case here, we will briefly touch on the most commonly used terminologies when talking about exhaust systems.
Manifold or Header
In a common manifold, a single assembly shares all the cylinders that collects the exhaust gasses and then channels them into one pipe. In the case of a header, each cylinder gets its own pipe that flows into one larger pipe, called the collector. See the image in this regard. The header is a performance manifold designed for optimal flow of the exhaust gases because it makes it easier for your engine to push exhaust gases out of the cylinders by eliminating the manifold’s backpressure. The manifold or headers can be made of steel, aluminium, stainless steel, or cast iron.
The header-back is the part from the outlet of the header to the final vent, that is, to the open end/back of your vehicle (the tailpipe). We will discuss this system in broader details later.
The cat-back refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent, that is, to the open end/back of your vehicle (the tailpipe). The cat-back system generally use a larger diameter pipe than your normal stock system. We will discuss this system in broader details later.
The turbo-back is the part from the outlet of a turbocharger to the final vent, that is, to the open end/back of your vehicle (the tailpipe).
The catalytic converter, normally found between the exhaust manifold and the muffler, have the main purpose of reducing harmful emissions of hydrocarbons, carbon monoxide and nitrogen oxides that may escape into the atmosphere. Catalytic converters transform these poisonous and harmful exhaust components into water vapour and carbon dioxide. It is becoming a trend by several automotive manufacturers to combine high-powered catalytic converters with diesel particulate filters. As mentioned in the working and purpose discussion above, the catalytic converter is there for a reason, albeit a legal one, so it is illegal to remove it and not to have a catalytic converter in your vehicle.
The muffler (also known as a silencer), controls the exhaust emissions and it quietens the engine down. It looks like a large round or oval chamber (usually, but not always, found near the back of the vehicle) and it consist of resonating chambers covered by sound absorbing material. The chambers and material lessen the sound escaping from the exhaust pipe. The downside of some mufflers is the backpressure they can create; backpressure can causes the vehicle to have less power and it can affect fuel efficiency. Just as a catalytic converter filters out harmful air pollution, mufflers protect your ears and the environment from noise pollution.
The tailpipe is the end of the final length of exhaust pipe where it vents (generally the only visible part of the exhaust system on a vehicle). It often ends with just a straight or angled cut, but may include a fancy tip that is often of larger pipe diameter and mostly chromed.
Lake pipes refer to a set of exhaust side pipes; with these, your exhaust is routed from the manifolds along or beside the bottom of your vehicle’s body, beneath the doors. They offer a performance boost as they have less backpressure than conventional exhausts.
In all modern fuel injected vehicles, there is an oxygen sensor mounted in the exhaust manifold or close to it in the exhaust pipe. The purpose of the sensor is to measure how much oxygen is present in the exhaust. Your vehicle’s engine control unit (ECU) can add or subtract fuel to obtain the correct mixture (AFR – air–fuel-ratio) for maximum fuel economy.
Hangers & Brackets
Most exhaust systems are suspended from the underside of the vehicle and kept in place by a series of brackets and hangers. More about these in the maintenance part of our discussion.
Now that we are more familiar with the terminologies when it comes to exhaust systems, let us have a look at the different types of exhaust systems and components.
Exhaust systems are available in many different styles and configurations. You may be familiar with some of these, with others maybe not as much. First, we will look at the different types of exhaust vents, that is, the open end (as seen from the back of a vehicle), we will then look at the three main types of exhaust systems as discussed by David Fuller (2012), namely the header-back, cat-back, and axle-back. After that, we will touch on some differentiations made when it comes to exhaust systems. You should keep in mind that aftermarket exhaust systems (depending on the type you choose) will come with a combination of header or intermediate pipes, crossover pipes, catalytic converters, mufflers, and tailpipes. It is also noteworthy that diesel exhaust kits differ from normal exhaust systems. Where normal exhaust systems use catalytic converters, the diesel exhaust requires a diesel particulate filter (DPF).
When you look at a vehicle from the backside, you may see either one of the following tailpipe configurations:
Single Exit (back)
A single exhaust tip exits from the rear and it is safe to say that this is the most common type found in vehicles nowadays. This system is easy to install and not costly. Because of this, the single exit system is readily available. It does have a downside because it is considered not to be among the most efficient systems of the lot. This inefficiency may be addressed by considering an aftermarket single exhaust system. An aftermarket system will provide a significant upgrade in performance because larger pipe diameters and less restrictive mandrel bends are incorporated into an aftermarket system.
Dual Exit (paired – back)
You sit behind a vehicle and you see two tailpipes, paired next to each other on one side of the vehicle, staring back at you. That is how a typical dual side system will look like, and it should not be confused with a dual rear system (which will be discussed next). The dual side system utilize the same configuration as a single exhaust system, that is, one head pipe, a converter, a muffler, but with two tips exiting from the muffler. The dual side system usually utilize smaller pipes, which can create a deeper sound. Some dual exhaust system designs features two separate pipes that run from the headers all the way to the tips at the back. At times two catalytic converters and two mufflers are present, one in each pipe. According to Fuller (2012), performance enthusiasts prefer this design because of the distinctive growl of the dual mufflers and the high-flow capabilities of two separate exhaust passages for each bank of engine cylinders.
There is nonetheless a downside to this system in the sense that it can potentially create uneven backpressure. If there is an imbalance between the two sets, then the one bank of cylinders can back up and make less horsepower than the other makes. This problem can be eliminated by the so-called “dual crossover system” that will allow exhaust gases to flow freely between the two sets of pipes, thereby eliminating excess backpressure on any one of the sides.
Dual Exit Side
A dual side system incorporates two pipes next to each other on the left or right side of the vehicle, that is, it does not exit at the back of the vehicle.
Dual Exit (unpaired – back)
The dual rear system (not to be confused with the dual side system), is where two separate exhaust pipes (with one on each side of the vehicle) exit at the rear. The dual rear system gives a much deeper sound, as if your vehicle has a very powerful engine. This system is more efficient at removing outlet gasses than the single system; it is also more expensive and more difficult to install.
Opposite Dual Exit (unpaired – back)
The difference between the dual rear system and the opposite dual system is that the former system do not bend, while the latter system wrap around the wheel, using the bend to add to the filtering process. Therefore, with the opposite dual system we have two separate exhaust pipes bending around the rear tyres to exit out the back.
The type of tailpipe configuration you may choose, will depend on your own preference, the make and model of your vehicle, and the ability to install any of these on your vehicle (some vehicles can only accommodate the one or the other). Let us now look at the types of systems that Fuller (2012) highlighted.
In the terminology part, we already became acquainted with this term. The header-back systems replace everything from the header collector to the tailpipes. By way of a header-back system, you can enlarge the diameter of your entire exhaust system. In doing so, you will enable your exhaust system to cater for a greater flow of exhaust gasses (in respect to volume). Installing a header-back system is expensive and tougher to install, compared to the cat-back or axle-back systems because you will be replacing nearly the entire exhaust system.
Another term we acquainted ourselves with earlier, is the cat-back system. This system will replace exhaust components from the catalytic converter all the way to the back, including the muffler and tailpipe. Depending on the make and model, they may come with a mid-pipe, X-pipe, H-pipe or a Y-pipe. Many vehicle owners prefer the cat-back systems, and mostly because it is a relatively simple modification, it gives good power gains and better efficiency due to freer exhaust flow. It also gives an aggressive exhaust sound (that is still in tune with emission laws) because of the retained catalytic converter.
You may recall that we mentioned that there is a difference between a diesel and a petrol exhaust, and that the difference lies in the fact that the exhaust system of a petrol vehicle uses a catalytic converter, while the diesel exhaust requires a diesel particulate filter (DPF). Therefore, instead of using the term “cat-back”, we use the term “filter back”, because we cannot work from a catalytic converter backwards, we rather work from the diesel particulate filter backwards.
This system only includes components from the rear axle to the exhaust tip. It does not include an intermediate pipe and it is not so difficult to install. The axle-back can also deliver a performance sound as in the case of the cat-back. For vehicles with front wheel drive, the cat-back would start near the area where your axle would be, right in between your rear tyres.
High-performance systems are more efficient and more expensive than all the systems mentioned thus far. Specialized companies produce these aftermarket products, and aside from being more efficient at removing and filtering gases, they can substantially alter the sound and the look of a vehicle, as well as boost its performance.
Apart from the placement of the tailpipe and the different types of exhaust systems, there are some other factors that you may take into consideration when considering a new exhaust system, or just understanding your vehicle’s current system.
Mild Steel vs. Stainless Steel
It is important to know that the material used to make an exhaust system, also plays a defining role. An exhaust system made from mild steel is cheaper than a stainless steel one, but it will rust or corrode much faster. A stainless steel system will resists corrosion, but it will cost you more.
Mandrel bent & Press bent
Take note of the fact that a mandrel bent exhaust have bends in the exhaust that are smooth and do not neck down. A press bent exhaust, has so-called dents in the bends that causes a disruption in flow. This is not very conducive for power production.
Maintaining Your Exhaust System
Now that we are better acquainted with exhaust related terminologies and with the different types of exhaust systems available from which to choose, it is now time to say a few words on exhaust maintenance. Maintenance? Do you really need to do exhaust maintenance? The exhaust system is an essential part of your vehicle but it rarely gets the attention it deserves. If you care about your fuel efficiency, the environment and your safety, then you would want to keep the exhaust system in a good working condition. Here are a few headers on how to do exactly this:
Frequently inspect your exhaust system to ensure there are no holes and/or cracks in the system. This is an important safety feature because you would not want harmful fumes to enter the vehicle’s interior, now would you?
Exhaust manifold and gaskets
Check the manifold, headers and gaskets for any cracks or holes. If any of these are present, it will surely cause exhaust leaks that will affect safety, performance and cause unnecessary noise.
It is important to realise that cracks, damaged wires or blocked intakes can cause incorrect fuel/air mixture adjustments. With the passing of time, oxygen sensors may wear out and become less accurate. If this happens, your vehicle will surely show poor fuel economy.
Catalytic converters are not exempt from damage. They can overheat and even clog up, and if you add some dents and corrosion to the mixture, you could be sure of a catalytic converter that will cause a loss of power, a rough idling, air pollution, heat from the floor, a sulphur smell and excessive noise.
Hangers, clamps and brackets
Hangers, clamps and brackets ensure that the exhaust system stays snugly in its place. Any excessive rust or broken clamps, brackets, hangers and bolts, may cause the exhaust components to hang dangerously low. This is a safety issue, not only for yourself but for other road users too.
You usually just get into your vehicle, start the engine, and drive off. I mean, it makes little sense to start your vehicle and then get out and walk to the back and stare at the exhaust tailpipe… Well, maybe that is not such a senseless idea. Do yourself a favour, see what comes out of the tailpipe after you started your vehicle and leave it to idle. Water! Yes, this is a by-product of combustion and the catalytic converter, but this will evaporate if you drive for a reasonable distance. Short trips (let us be economical and say trips less than 20 minutes long) can considerably shorten the lifespan of your exhaust system. When you shut your engine down, the water vapour in the pipes will condense and turn back into liquid. On a short trip, the water never has a chance to get hot enough to evaporate; it will just stay in the system and peacefully do its job as nature intended whenever it gets into contact with metal – and that is to rusts away the pipes. If you have no other option than to drive for short distances, strongly consider replacing your system with stainless steel. It is hard to prevent your exhaust system from rusting, so the better the quality of stainless steel used, the more likely your exhaust is to hold up for much longer.
Black soot inside tailpipe
Back to your tailpipe again, and please, do not do the following while your exhaust is still hot. Take a finger and give it a whirl inside the tailpipe. The chance that your finger will be full of black soot is highly likely. So what happens? The gasses released through your exhaust system, are among others carbon dioxide, carbon monoxide and hydrocarbons. All of these contain carbon, and on its way out of the system, it fuses to the insides of your exhaust, turning it black in the process. An excessive build-up of carbon can hamper the release of exhaust fumes and negatively affect your vehicle’s performance and efficiency. Yes, before you ask, you can indeed cleanse the inside of it, that is, as far as you can reach into the tailpipe. To do this, you will need to apply a degreaser to the inside and outside of the exhaust tip to loosen the caked-on carbon deposits and rust. Reach into the back of the tailpipe as far you can and use a dry old cloth for this purpose. Leave the degreaser to soak, as recommended in the instructions of the product, and then scrub the degreaser off in small circular motions with the use of steel wool. Repeat this process if there is an excessive build-up of soot.
Did you ever think that a seemingly simple system, such as the exhaust system, could be so complex? At Steves Auto Clinic, we specialise in vehicle maintenance, and we always do our best to keep our readers, customers and every other vehicle owner, up to date with maintenance hints and advice. Apart from that, we also have branches countrywide, filled with specialised equipment, highly qualified mechanics, and very friendly staff that are ready and willing to assist you with any vehicle related issue. If you want something checked, fixed, diagnosed or enhanced, then you are at the right place, just visit your nearest Steves Auto Clinic.
Sources consulted during the writing of this article:
- Fuller, D. 2012. Exhaustive research: How to choose an aftermarket exhaust system. Online available at: https://www.onallcylinders.com/2012/06/07/exhaustive-research-how-to-choose-an-aftermarket-exhaust-system/ Accessed on 24 August 2018.
- Wikipedia. 2018. Exhaust system. Online available at: https://en.wikipedia.org/wiki/Exhaust_system Accessed on 24 August 2018.
Images used in this article:
- Image 1. – WheelZine. 2018. A look at the difference between exhaust manifolds and headers. Online available at: https://wheelzine.com/difference-between-exhaust-manifolds-headers Accessed on 25 August 2018.