A muffler ( silencer in many non-US English speaking countries) is a device for decreasing the amount of noise emitted by the exhaust gas of an internal combustion engine.
The US Patent for an ‘Exhaust muffler for engines’ was awarded to Milton 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”.
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 acoustics 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
tuned to cause destructive interference, wherein opposite sound waves cancel each other out.
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 Aesthetics Acoustics preferences. Although the Law of altering a motor vehicle's OEM exhaust system varies by jurisdiction, in many developed parts of the world, modification of a vehicle'
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
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
Trade-off between power increase and noise reduction
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”
Several such exhaust systems that utilize various designs and construction methods:
Vector muffler - for larger diesel trucks, uses many concentric cones, or for performance automotive applications, using Flowmaster to cause exhaust impulses to cancel each other out.
Spiral baffle muffler - for regular cars, uses a spiral-shaped baffle system
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