Motorcycle mufflers

Motorcycle muffler is an indispensable part in the history of motorcycle development, and the development history of motorcycle muffler is as long as that of motorcycles. After the engine has done work, the exhaust stroke follows. Exhaust is to exhaust the exhaust gas in the cylinder. Since the exhaust gas at this time is of high temperature and high pressure, it is directly discharged from the exhaust pipe, which will be very noisy. The function of the muffler is simply that the airflow discharged from the engine passes through the porous pipe and the partition in the muffler and recirculates repeatedly, the noise is gradually attenuated to achieve the purpose of silencer.

The muffler is a combination of multi-stage shunt and partial pressure. Its working principle is roughly as follows:

1. Intake: At this time, the intake valve opens, the piston descends, and the mixture of gasoline and air is sucked into the cylinder.

2. Compression: At this time, the intake valve and exhaust valve are closed at the same time, the piston moves up, and the mixture is compressed.

3. Combustion: When the mixture is compressed to a small amount, the spark plug ignites the mixture, and the pressure generated by combustion pushes the piston down and drives the crankshaft to rotate.

4. Exhaust: When the piston descends to a lower point, the exhaust valve opens, exhaust gas is discharged, and the piston continues to move upward to discharge excess exhaust gas.

Types of muffler

A. According to the principle of silencing

1. Resistive muffler
This kind of muffler uses the sound absorption effect of the sound-absorbing material or sound-absorbing structure to attenuate the noise propagating along the pipeline with the distance, so as to achieve the purpose of sound elimination. Commonly used sound-absorbing materials are glass fiber yarn, low-carbon steel wire mesh, felt, etc. This type of muffler has a good silencing effect on high-frequency noise, but the low-frequency silencing performance is poor. In addition, because the sound-absorbing material is easily melted by the high-temperature exhaust gas discharged from the engine, the service life is short, and it is easy to be blocked by carbon deposits, sludge, etc., which reduces or loses the muffling effect, so a single resistive muffler is rarely used on motorcycles.

2. Resistant muffler
This type of muffler uses the sudden expansion (or contraction) of the pipe section or the bypassing of the resonant cavity to reflect the sound waves of certain frequencies propagating along the pipe to the direction of the sound source at a sudden change, so as to achieve the purpose of sound elimination. It is more suitable for eliminating low and intermediate frequency noise, but has a poor effect on high frequency noise.

3. Impedance compound muffler
This kind of muffler is a combination of resistive muffler and resistive muffler's noise elimination principle through an appropriate structure, and has the noise elimination characteristics of both. Because the noise frequency band generated by the noise source of motorcycle engine is relatively wide, in order to obtain better noise reduction effect in the wide frequency range of low, medium and high, most motorcycles choose this kind of impedance compound muffler.

B. According to the structure of the muffler

Motorcycle mufflers can be divided into two types: barrel muffler and box muffler according to the shape and structure, which will be introduced separately below.

1. Cylinder muffler

This type of muffler is generally a resistant or impedance compound muffler, which is mostly used on medium and large displacement motorcycles.

  Cylinder muffler is generally composed of exhaust pipe, connecting screw sleeve, muffler tube and cylinder core. An oil-impregnated asbestos sealing ring is installed in the connecting screw sleeve to prevent air leakage at the interface between the exhaust pipe and the muffler tube. There are several partitions welded in the muffler cylinder, and the muffler cylinder is divided into several muffler cavities (N expansion chambers and 1 resonance cavity). There are inverted triangular diversion grooves and many small holes on the cylinder core. When exhaust gas enters the muffler through the exhaust pipe at a high speed, as the cross-sectional area of the muffler tube gradually increases, the airflow is expanded, the flow velocity is reduced, and the powerful pulsating noise is attenuated. When the airflow continues to flow through the expansion chambers, due to the blocking of the partitions, the airflow can only pass through the throttle holes and the cylinder core on the partitions, so the airflow is suddenly compressed, divided into many small streams, and then suddenly expanded. Multiple mutations to reduce exhaust noise.

2. Box muffler

General mopeds, especially seat cars, have relatively small installation space, so box-type mufflers are often used, which are composed of a shell, sound-absorbing filler, and muffler tubes.

C. According to the material of the silencer

The modified pipes of the muffler can be divided into aluminum alloy motorcycle exhaust pipes, stainless steel motorcycle exhaust pipes, carbon fiber motorcycle exhaust pipes, titanium alloy motorcycle exhaust pipes, etc., each with its own advantages. Aluminum alloy tubes are lighter in weight, more colorful, and cheaper. However, the surface of the tube is easy to wear and is not as durable as stainless steel tubes. Stainless steel tubes are heavier and less colored, but they are more durable and have a heavier sound than aluminum alloy tubes. Therefore, most friends who play modification like to choose stainless steel tubes. However, the high price of the material itself is still unable to make it truly highly popular. Carbon fiber tubes are lighter in weight, generally black carbon fiber, and their durability is not as good as stainless steel.

Modification of the silencer

If the exhaust pipe cannot quickly exhaust the burned exhaust gas, the next intake stroke must not be able to quickly and completely inhale fresh air; especially the waste exhaust remaining in the combustion chamber at this moment will also affect the next time. Combustion efficiency, in this way, the horsepower performance will naturally not be ideal, which is why the exhaust pipe is modified.

In a word, the modification of the exhaust pipe is mostly started from the middle and tail section. The common methods are nothing more than thickening the pipe diameter and reducing the muffler. In the modification of the middle section of the exhaust pipe, another important element is the catalyst. Although the basic function of the catalyst is to purify the exhaust gas, it also has the function of eliminating resonance to the cockpit. From the perspective of the modification, the catalyst composed of many kinds of precious metals densely formed is indeed a major culprit obstructing the smoothness of the exhaust, and it is an annoying hot spot, so many people will choose to replace it, often just this small straight-through If you change, you can feel that the exhaust is much smoother and the sound will not be stuffy inside.

Regular maintenance of the muffler

Because the fuel is not completely burned when the engine is working. In addition, the fuel contains certain impurities. Therefore, when the high-temperature exhaust gas from the engine passes through the exhaust muffler, carbon deposits will be generated on the muffler's cylinder core and partitions. Over time, the accumulated carbon deposits will block the airflow channel. , So that the exhaust resistance increases, the noise reduction performance is reduced, the engine is weak, and the normal driving of the vehicle is affected. In severe cases, the exhaust pipe will turn blue and the engine will be damaged due to excessive temperature. Therefore, regular maintenance and cleaning of motorcycle mufflers are necessary. Under normal conditions, the carbon deposits on the muffler tube and cylinder core should be removed every 3000 kilometers; the exhaust pipe and muffler should be removed every 6000 kilometers, and the exhaust port and exhaust pipe of the cylinder should be removed. The carbon deposits in the muffler are removed.

The performance of the muffler not only affects the size of the motorcycle noise, but also has a greater impact on the engine's power, fuel consumption, torque and other performance. Therefore, it is necessary for every motorcycle user to understand the principle, structure and maintenance knowledge of motorcycle mufflers.