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Muffler (silver) and exhaust pipe on a Ducati motorcycle
This picture of an old muffler which is cut open for repairs shows the insulation, chambers and piping inside the muffler housing.

A muffler (silencer in many non-US English speaking countries) is a device for decreasing the amount of noise emitted by the exhaust of an internal combustion engine.


The US Patent for an ‘Exhaust muffler for engines’ was awarded to Milton O. Reeves and Marshall T. Reeves of Columbus, Indiana of the Reeves Pulley Company on 11 May 1897. US Patent Office application № 582485 states that they “have invented certain new and useful Improvements in Exhaust-Mufflers for engines”.[1]


Dual tailpipes attached to the muffler on a passenger car
A CRX muffler detached from the car.

Mufflers are installed within the exhaust system of most internal combustion engines, although the muffler is not designed to serve any primary exhaust function. The muffler is engineered as an acoustic soundproofing device designed to reduce the loudness of the sound pressure created by the engine by way of acoustic quieting. The majority of the sound pressure produced by the engine is emanated out of the vehicle via the same piping used by the silent exhaust gases. The emitted noise 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.[2][3]

An unavoidable side effect of muffler use is an increase of back pressure, which decreases 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.

Some vehicle owners remove or install an aftermarket muffler when engine tuning in order to increase power output or reduce fuel consumption because of economic or environmental concerns, recreational pursuits such as motorsport and hypermiling and/or for personal aesthetic acoustical preferences. Although the legality of altering a motor vehicle's OEM exhaust system varies by jurisdiction, in many developed parts of the world, modification of a vehicle's exhaust system is usually highly regulated if not strictly prohibited.[4][5][6]

There are 2 main types of performance mufflers based on the installation type.

  • Vehicle-specific. These mufflers are made for a specific vehicle application and are direct replacement to the stock muffler. They will work on the vehicle the right way and employ factory mounting points from the stock muffler[7].
  • Dimension-specific or universal. To pick the right universal muffler for the specific vehicle application, one has to measure their exhaust (inlet, outlet, muffler diameter) and then select from the mufflers that correspond to these characteristics.

Aftermarket mufflers usually feature different pitch and may alter the way vehicle performs due to back pressure decrease[8].

A muffler on a large diesel-powered truck

Trade-off between power increase and noise reduction

A cutaway view of a muffler showing the interior pipes and chambers.

When the flow of exhaust gases from the engine to the atmosphere is obstructed to any degree, back pressure arises and the engine's efficiency, and therefore power, is reduced. Performance-oriented mufflers and exhaust systems thus strive to minimize back pressure by employing numerous technologies and methods to attenuate the sound. For the majority of such systems, however, the general rule of “more power, more noise”[9] applies. Several such exhaust systems that utilize various designs and construction methods:

  • Vector muffler - for larger diesel trucks, uses many concentric cones,[citation needed] or for performance automotive applications, using angled baffles to cause exhaust impulses to cancel each other out.
  • Spiral baffle muffler - for regular cars, uses a spiral-shaped baffle system[10]
  • Aero turbine muffler - creates partial vacuums at carefully spaced out time intervals to create negative back pressure, effectively ‘sucking’ the exhaust out of the combustion cylinders[11]

See also


  1. ^ "Exhaust Muffler For Engines Muffler Patent". Google. Retrieved 22 June 2014. 
  2. ^
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^ Grayen, Michael (August 2014). "Performance Mufflers: Installation, Fitment, Specs". 
  8. ^ D. W. Herrin (2012). "Vibro-Acoustic Design in Mechanical Systems" (PDF). University of Kentucky. 
  9. ^ "Exhaust Theory". NSX Prime. Archived from the original on 4 November 2013. Retrieved 22 June 2014. 
  10. ^ "Spiral Turbo Specialties:". Spiral Turbo Specialties. Retrieved 22 June 2014. 
  11. ^ "Aero Turbine Series Performance Exhaust Mufflers". Pickup Specialties. Archived from the original on 16 May 2014. Retrieved 22 June 2014. 

External links

  • Howstuffworks: "How Mufflers Work"
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