What is Muffler and how does it work?

What is a Muffler?

A muffler (North American and Australian English) or silencer (British English) is a device for reducing the noise emitted by the exhaust of an internal combustion engine—especially a noise-deadening device forming part of the exhaust system of an automobile.

Mufflers are installed within the exhaust system of most internal combustion engines. The muffler is engineered as an acoustic device to reduce the loudness of the sound pressure created by the engine by acoustic quieting.

The noise of the burning-hot exhaust gas exiting the engine at high speed is abated by a series of passages and chambers lined with roving fiberglass insulation and/or resonating chambers harmonically tuned to cause destructive interference, wherein opposite sound waves cancel each other out.

An unavoidable side effect of this noise reduction is a restriction of the exhaust gas flow, which creates back pressure, which can decrease engine efficiency. This is because the engine exhaust must share the same complex exit pathway built inside the muffler as the sound pressure that the muffler is designed to mitigate.

A cutaway muffler showing the interior pipes and chambers which reduces Horsepower

Some aftermarket mufflers claim to increase engine output and/or reduce fuel consumption by slightly reduced backpressure. This usually entails less noise reduction (i.e., more noise).

How does a muffler work?

If you’ve ever heard a car engine running without a muffler, you know what a huge difference a muffler can make to the noise level. Inside a muffler, you’ll find a deceptively simple set of tubes with some holes in them.

These tubes and chambers are actuall­y as finely tuned as a musical instrument. They are designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out.

Inside a muffler, there are tubes with perforations that direct the sound waves through the inside of the muffler and out the end. Sound waves will enter through a central tube, hit the back wall, pass through a hole and enter the center chamber. Every aspect of the muffler is designed to aid in canceling out noise.

Mufflers use some pretty neat technology to cancel out the noise. In this article, we’ll take a look inside a real car muffler and learn about the principles that make it work.

But first, we need to know a little about sound.

Signs You Need a New Muffler

Aside from visible signs of rust, you’ll most likely hear, feel and smell a bad muffler before actually seeing one.

  • Noise – Nine times out of ten, a noisy muffler is a bad muffler. If yours seems much louder than it was in the past, it may be time to consider a replacement.
  • MPG – If your car is feeling sluggish and you notice a drop in fuel efficiency, your muffler may be doing a poor job moving air through the exhaust.
  • Smell – If you notice stranger-than-usual smells from your muffler, don’t ignore it! A leak can cause exhaust fumes to be trapped inside which can be dangerous, so don’t let a smelly muffler go unattended.

Types of Mufflers

There are three types of mufflers and which is best for your car depends on your desired balance between noise and airflow. High-performance mufflers, which add horsepower to the engine, have a lot of airflows but also make the most noise. The stock muffler on your dad’s sedan may not offer much in performance but probably purrs like a kitten.

  • Glass Pack Mufflers – This is a straight-through design (it looks like a plain tube) and the simplest type of muffler available. A glass pack offers a good balance between noise and performance and isn’t likely to wake your neighbors when you drive home at night.
  • Chambered Mufflers – This is a common design on most cars and uses several dampening chambers inside the muffler to reduce noise as exhaust travels from chamber to chamber. These mufflers have the rectangular shape you’re used to seeing when picturing the typical muffler.
  • Turbo Mufflers – This is what you want for performance and, despite the name, doesn’t require even a turbocharger under the hood. Turbo mufflers use an s-shape inside the chamber to dampen some noise while maximizing performance.

How to Install a Muffler?

The good news, most mufflers require no welding or complicated tools to install. But if you’re still unsure about these steps, an Advance Auto Parts Team Member will gladly help.

  • Park on a level surface and engage the parking brake
  • Unhook the battery
  • Spray with penetrating fluid so that you can unscrew the clamps
  • Use an adjustable wrench or socket tool to unscrew and loosen the clamps
  • Remove the old muffler and slide the new one onto the exhaust pipe
  • Re-attach the clamp to secure in place (you may need new clamps if the old ones are rusted)