What Is a Muffler and What Does It Do?

Gearheads come in all shapes and sizes, but we're all drawn in by a similar experience. At some point or another, when you were innocent and none the wiser, you were exposed to that magical automotive music. The menacing note an engine belted out as it got down to business or idled pierced your soul and littered your skin with goosebumps. From that moment on, you were hooked. Mufflers play a big role in that noise you heard, and if better sound is the goal, that'd be the first upgrade you'd seek to make to your own car. 

However, there are so many options on the market, and you can’t help but wonder what makes one different from another. That’s exactly what The Drive is here to help you with. In this post, you will learn what a muffler is, what it does, and how they work.

A muffler is a simple device used to reduce and manipulate the noise emitted by an internal combustion engine. It's important not to confuse mufflers with resonators, as mufflers control noise across the board while resonators target low RPM frequencies to reduce drone and other sound-related issues. That isn't to say resonators aren't a great item for tuning the note of an engine—it's just not the same as a muffler.

There are different types of mufflers, and each manufacturer will use different design methods to achieve the sound and flow characteristics customers are after. That said, knowing more about the common designs will give you a better understanding of how most mufflers work.  

These are what many performance enthusiasts prefer because of the flow advantages that the straight-through configuration offers. These feature a metal casing that has a perforated tube running through the center. The inner tube is surrounded by a packing material which absorbs the sound waves as the exhaust gases flow through. 

These feature fiberglass packing to combat noise levels and are likely the first thing to come to mind. However, you shouldn’t assume all packed mufflers are all about raw sound. Manufacturers can tweak the design to achieve a particular tone. For example, MagnaFlow’s iconic-sounding mufflers use packing a little more strategically than your most basic designs. 

This design is unique in that it incorporates a proprietary perforation core pattern and dual-stage packing material consisting of an initial stainless steel wool to absorb the heat from direct contact with the perforation core while providing the gases an expansion area to make full contact with the second stage of premium acoustic packing material. That’s how we get that distinct MagnaFlow sound.

These are an equally popular design, but they work very differently from packed mufflers. These feature specially designed chambers to get sound waves to bounce off one another. Manufacturers will also typically include other tuning structures within the chambers, such as baffles, to tweak the sound. That said, most work to emphasize the throaty, deeper note of a big displacement engine. 

This is another design you're bound to run into. These work with a series of perforated tubes that direct exhaust gases in either an S or roundabout pattern through the body of the muffler. Some turbo mufflers do use packing around the perforated tubing to control sound levels, but that’s not always the case. While turbo mufflers are usually the most restrictive of the bunch, they remain a favorite for their ability to control sound levels and reduce drone. That said, there are plenty of examples of turbo mufflers that are docile down low, while the wide-open throttle is raspy and comparable to traditional packed mufflers. 

Engines have always been loud and people have had ears for as long as they have existed. It shouldn't really come as a surprise to find out that Milton O. Reeves put the first patent on one way back in 1897. 

Naturally, mufflers would evolve throughout the next 100-plus years, but it would be some time until the most popular names would enter the market. Walker Exhaust put itself on the map with its louver tube muffler in 1932, but it wasn’t until 1966 that Thrush arrived on the scene and Cherry Bomb in 1968. From the ‘70s well into the ‘90s, more iconic brands, such as MagnaFlow, Borla, Corsa, Flowmaster, and Dynomax, would stake their claims with high performance exhaust systems and signature mufflers.

Which muffler is the loudest? Which is the quietest? You can sum it up by saying that packed mufflers generally are the loudest, turbo mufflers are the quietest, and chambered mufflers land right in the middle. It's really not that simple, though, as there's more to consider than the basic design. Some physical characteristics play a major role in how loud a muffler is. Overall size, in particular, is something to think about when balancing sound levels.

"As the volume, cross-section or length of the muffler is reduced the loudness of the muffler will be greater and as the volume, cross-section or length of the muffler is increased the loudness of the muffler will be lessened," MagnaFlow said. 

The direction of flow through the muffler is also a key player.

"Another consideration for sound is the inlet/outlet configuration," MagnaFlow said. "While it may seem that this might lend itself to fitment only, the configuration will determine loudness as well. A center/center has a straight path and will be louder than a center/offset muffler of the same core diameter and body size and a center/offset will be louder than the offset/offset. Basically, as the offset gets bigger between the inlet/outlets, there is more pipe as the perforation core is now longer as it’s traveling diagonally through the muffler body. In addition, the bends inside of the muffler will contribute to creating some turbulence as the gases have to change direction which also contributes to creating a quieter muffler."

What if you don't want a packed muffler? Say you want something like a turbo muffler instead. Well, case length's impact on sound levels is universal. Otherwise, different traits come into play for different mufflers. As said earlier, turbo mufflers sometimes feature packing to muffle sound alongside the existing design. 

You already know that chambered mufflers can use their namesake to combat noise levels. The number of chambers in a muffler and tweaks to certain design elements within each will have a direct impact on sound characteristics. 

The point is that there's a little to know about each before you settle for one over another. The good news is that most manufacturers offer cutaways and are very helpful at providing the details you need to know what to expect from a particular muffler. The only problem is that you won't know what it sounds like or how loud it is until it's on your car. It's best to hear mufflers in person on similar platforms to what you're working with beforehand unless you're willing to experiment and try different things out. 

Want the short and skinny of it? No problem. Some are visual learners anyway, which is why we wanted to include a video that explains how mufflers work. The clip below talks about the same three types of mufflers discussed above. Only, their cutaways are much more helpful for helping you see what each muffler does to manipulate sound characteristics. 

You have the questions, The Drive has the answers.

A. That really depends on who you are and who you're around. Some people feel that the best-sounding engines are those without mufflers. However, there's no arguing that the sound can be hard to deal with. Which is why mufflers exist in the first place. It won't hurt performance, in fact the opposite might be true.

A. All mufflers have a direct impact on performance. The easier it is for exhaust gases to move, the better the engine can perform. That's why aftermarket muffler designers go through leaps and bounds to make sure their mufflers flow as freely as possible.

A. When it comes to getting the most power out of your engine, straight-through packed mufflers are tough to beat. So much so, that you’d be hard-pressed to find any all-out performance build that’s required to run mufflers without some kind of packed muffler on board. That is unless the rules of a particular event force them to go with something closer to a stock-type muffler.

A. Your car will need to have a muffler for on-road driving, and you can get a ticket for not having one. However, if it's a race-only vehicle and there are no event rules in place surrounding mufflers, you'll be fine. Also, you should read into local laws before turning to an exhaust cutout as a loophole.

A. A muffler's job is to reduce sound, but it can accentuate certain frequencies to manipulate the engine tone. That said, it can only do so much. The sounds an engine produces is determined by the design of the engine itself.