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How Your Muffler and Exhaust System Work

Alex Palmeri
September 26, 2018

how muffler works

Electric vehicles are gaining popularity — but the fact is, most of us still drive a plain, old gasoline-burning car or truck. If you do, too, then one of your car’s most important features is its exhaust system, which includes a muffler.

Engines are loud, and they put out a lot of fumes that aren’t good to breathe. The exhaust system is there to dispel the byproducts of burning fuel, directing the fumes safely away from the cabin while cutting the loud noise of the engine. 

Let’s look at the components of the exhaust system, how they work, and what to do to make sure your system is doing its job.

What does the exhaust system do?

Burning fuel produces exhaust fumes — this is true of the wood in your fireplace, the coal in your power plant, or the diesel or gasoline in your vehicle. Without an exhaust system, your engine would be extremely loud, and poisonous fumes would enter the cabin. 

Exhaust leaves the engine through the cylinder head, and the first cars were made with a pipe attached to this exit point. This pipe was bent in multiple areas to align with the bottom of the vehicle, and in many cases consisted of multiple pipes connected with various flanges and gaskets. This system would eventually lead to a tailpipe at or toward the rear of the vehicle, where exhaust fumes would be released away from the passengers. 

The general idea remains the same today. But, as vehicles advanced, mufflers and resonators were added to reduce noise. Eventually, catalytic converters were introduced to reduce emissions, and now we even have special exhaust valves on performance-oriented cars.

Get your exhaust problem diagnosed by a professional
 

How do mufflers and resonators work? 

Odds are you’ve heard of the muffler, and you may also have heard of the resonator. Both parts reduce the noise your engine naturally makes, but they have different specific purposes. 

Mufflers

The muffler is a metal canister usually situated in the rear of the vehicle. It’s fed by an exhaust pipe from the engine and can be constructed a few different ways internally. Some mufflers are made with metal baffles, some with internal tubes and some with an insulator such as fiberglass. 

They are designed to not only direct exhaust flow but to cancel sound waves produced by the engine. Because every engine produces different sound waves, a muffler needs to be specifically designed for its engine. Sound engineers spend many hours designing a muffler that can internally cancel out most sound waves while still providing maximum flow for the best performance and fuel economy. 

Mufflers are designed to muffle the engine sound at all times, but in some cases, a specific frequency can only be heard at a certain engine load or RPM level. To reduce a humming from the exhaust at a specific operating range, resonators are introduced. 

Resonators

Resonators are typically a little smaller than mufflers and are installed before the muffler. You can think of a resonator as an echo chamber. It’s generally a straight-through design with perforated walls, and some use an insulator. 

Sound waves bounce around the resonator and either cancel each other out or are absorbed before entering the muffler. The combination of both a muffler and resonator — and in some cases, two of each — have made modern cars very quiet without sacrificing much performance.

How do catalytic converters work?

A catalytic converter, sometimes just called a “cat,” is an emissions control device installed in the exhaust system. It has no effect on noise but instead reduces the harmful exhaust gases.

The catalytic converter is a metal canister installed near the engine. It contains precious metals such as platinum, palladium and rhodium, and when raw exhaust flows through it, multiple chemical reactions occur. The final product is an exhaust that's free of nitrogen oxides, carbon monoxide and hydrocarbons, three gases that are very harmful not only to the environment but also to humans. Catalytic converters can reach temperatures as high as 1,600 degrees while the engine is running.

A catalytic converter, muffler and resonator can all look similar, but the cat is usually smaller than the others and will have oxygen sensors installed before and after it to monitor how the engine is running and how the part is performing.

» LEARN MORE: Find a shop that can fix your exhaust system problem

What is ‘active exhaust’?

In an attempt to keep sports cars sounding like a sports car, even with the strict emissions and noise regulations imposed on automakers, some cars have what’s called an “active exhaust.” This usually consists of electronic or vacuum-operated valves that are installed before the muffler. 

During hard acceleration or high-speed cruising, these valves can open and bypass the muffler, creating a much louder and more aggressive exhaust note. The exhaust fumes are the same, having gone through the catalytic converter — only the sound level is affected. And since it’s only engaged during spirited driving, the car remains quiet during normal use. It’s the best of both worlds. 

Exhaust manifold

What else makes up an exhaust system?

Every internal combustion engine has exhaust manifolds. These bolt directly to the cylinder head and consist of either individual tubes for each cylinder, or one long tube with openings to each exhaust port. They are made of thick steel and have a collector that bolts up to the rest of the exhaust system.

Your exhaust system also contains various flanges that connect its pipes together. These may be metal-to-metal connection points using bolts and nuts to secure them. You may also have exhaust flange gaskets that are typically made of a high-heat graphite material. 

Some exhaust systems use flexible joints to allow for movement when the engine torques, and in order to hold the large exhaust system to the car, most manufacturers use hangers. These are made of very strong rubber and are bolted to the lower body of the car. The hangers also allow for some movement in the exhaust while going over rough terrain. 

The final part of the system is the only visible part from the outside: the tailpipe. Some cars have one, while some have two, but the idea is the same. These pipes direct the exhaust as far away from the cabin as possible so no one is breathing it in while driving. It’s usually a simple pipe connected to the end of the exhaust system either with a clamp or by welding.

» LEARN MORE: Get an estimate for your exhaust system repair

Exhaust system problems and maintenance

Most carmakers don’t require maintenance on the exhaust system outside of periodic inspections. Consult your owner’s manual for details. 

That said, the parts can wear out, most often because of rust. The majority of exhaust repairs are because holes have formed in either the pipes or the muffler. This will result in a much louder car and possibly an exhaust leak in the vehicle. 

Exhaust rattles are another fairly common issue. They could come from a broken catalytic converter or a failed mounting flange or hanger. 

It’s best to have your system inspected any time it’s in for maintenance. And if you live in an area that uses salt in the winter, use water to clean the outside of your exhaust system after the season has passed. 

Beware of cheap or poor-quality exhaust parts, especially catalytic converters. A lot of muffler shops will sell you mufflers and exhaust pipes that simply do not last nearly as long as the factory originals (also called OEM parts). If you don’t use OEM parts, it’s best to keep your receipt and make sure they have a warranty.  

But often, a vehicle’s exhaust components can last the life of the car. Because of this, automakers sometimes extend the exhaust warranty past the normal manufacturer’s warranty. Consult your paperwork before paying out of pocket for any exhaust repair, especially pricey catalytic converters.

Alex Palmeri

About the Author

Alex Palmeri worked nine years as a master technician at Mercedes-Benz of Chicago and is currently the foreman at a large fleet garage. He writes about automotive news, maintenance and racing, and runs a YouTube channel called Legit Street Cars.

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