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How Does Your Car's Exhaust System Work?

When your car is running, there are thousands of small explosions inside your engine every minute. Each one produces power by pushing against the engine’s pistons. But the explosions also produce leftover gases. They’re made up of potentially dangerous chemicals such as carbon dioxide, carbon monoxide, hydrocarbons and nitrogen oxides. These gases need to be routed away from the engine compartment so they don’t get into the cabin, and then into your lungs. That’s the basic job of a car’s exhaust system.

In modern-day vehicles, exhaust systems play other roles, too. Just letting those exhaust gases go straight into the atmosphere only means that more people can be affected by them. Further, all the constant engine explosions produce something else that can harm people: noise pollution.

Today’s exhaust systems have parts that are designed to deal with all of those issues.

What is an Exhaust Manifold?

For most cars, it all starts with the exhaust manifold. This is made of metal, usually cast iron, and connects the engine to the rest of the exhaust system. On one side of the manifold are individual tubes that connect to each of the engine cylinders. They merge together in the manifold and come out of the other side in a single tube. (Engines also have intake manifolds that go the other way. Here, a single source of fresh air is split into the separate tubes. The tubes then split off the manifold to take that air to the individual cylinders for combustion.)

What are Headers?

If you’re a hot-rod enthusiast, you may opt for “headers” instead of a traditional exhaust manifold. Headers also collect the exhaust gases from the different cylinders into one tube, but the individual tubes for headers are much longer. This reduces the pressure needed to force the exhaust gases through the system, increasing performance.

What Does an Oxygen Sensor Do?

An oxygen sensor is a part of the exhaust system that helps fine-tune the intake process. Often located in the exhaust manifold, the sensor measures how much oxygen is in the waste gases. In a perfect world, there wouldn’t be any. The engine would use exactly the right amount of oxygen needed to completely burn the fuel, and none of either would be left over. With a modern fuel-injected car, the ECU (engine control unit) analyzes the oxygen reading from the exhaust sensor. The ECU then can help ensure the optimum mixture of air to fuel in the engine cylinder by changing how much fuel is injected.

What is a Catalytic Converter?

The next major component for a mainstream exhaust system is the catalytic converter. It’s connected to the single pipe of exhaust gases collected from the separate cylinders. The catalytic converter “cleans up” three of the less common, but more dangerous, exhaust waste products. Most of what’s produced by the combustion process is nitrogen gas, carbon dioxide and water vapor. But there also are smaller amounts of nitrogen oxides, carbon monoxide and hydrocarbons.

In a catalytic converter, that stuff undergoes a chemical reaction as it comes into contact with certain rare elements. Those elements, or “catalysts,” do two things. First, they break the nitrogen oxides into nitrogen and oxygen. The latter element is then used by a second set of catalysts to “oxidize” the hydrocarbons and carbon monoxide. It’s a way of chemically burning off material that wasn’t combusted in the engine. Without getting deeper into the science, the bottom line is reduced emissions.

What Does a Muffler Do?

Waste gases aren’t the only things traveling through your exhaust system. So are sound waves. And it turns out that excessive noise has become a public health issue, even being linked to major heart problems. Mufflers rely on a few main strategies for reducing this noise pollution. One is to route the sound waves through tubes or chambers inside the muffler. The idea is to direct the sound waves so most end up canceling each other out. Additionally, sound-absorbing materials can be packed inside the muffler.

What is an Exhaust Resonator?

Some mufflers are specifically designed to tune the engine sounds to appeal to drivers. For example, part of the aggressive roar of a V8 engine comes from the way its muffler is designed. There also are cars with separate exhaust resonators to take this concept to the next level. Generally located in the exhaust system ahead of the conventional muffler, an exhaust resonator isn’t supposed to reduce the overall volume. Rather, it cancels out only the annoying frequencies and leaves the “good” ones as loud as ever.

What are Exhaust Tips?

At the end of the exhaust system is more hardware connected to the outlet of the muffler. In many cars, that’s a simple straight pipe. You also can add separate exhaust tips to improve the looks, sound and, to some degree, the performance of your vehicle.

What is a Dual Exhaust?

On the topic of exhaust tips, this is a good place to talk about the difference between those and a dual exhaust. Many sporty vehicles will have dual or even quad exhaust tips that are still part of a single exhaust system. That means the only benefits of the extra tips come during the relatively short distance between the muffler and the actual exhaust outlets. A true dual exhaust will have two independent exhaust systems. In a typical V6 or V8 dual exhaust, each bank of cylinders has its own system. As a result, the engine doesn’t have to push the gases from all six or eight cylinders through the same one exhaust pipe into a single muffler. Because the engine wastes less power doing that, there’s more available for performance.

What is a Cat-back Exhaust?

Another term thrown around by enthusiasts is a “cat-back exhaust.” Now, this doesn’t really refer to one specific kind of an exhaust system. It’s more a description of where along the system you’re making changes. If you’ve got a cat-back exhaust, it means you’ve upgraded all parts of your exhaust system behind your catalytic converter. That is, from the “cat” back.

Is a Turbocharger Part of the Exhaust System?

Sort of. You can think of a turbocharger as a single fan with a dual set of blades. They’re like two small wheels separated by a very short axle. One set of the blades is incorporated into the flow of exhaust gas from the engine. The more exhaust gas, the faster these blades spin. Since they’re connected to the other fan blades, those start spinning as well. The second set, however, is part of the intake system. They suck in more fresh air to force into the engine cylinders so they can create more power.

Krome, C. (2018). How Does Your Car's Exhaust System Work?. Retrieved from https://www.carfax.com/blog/how-does-an-exhaust-system-work


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