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The durability of the damping material depends on the type of motorcycle, riding style, mileage etc. Normally, single and twin cylinder engines produce a stronger exhaust gases wave pulse and a higher temperature. Often, riding on a race track requires noise control.
The insulating material should be replaced when you notice any visual changes on the muffler sleeve material or when the muffler exceeds the noise limit. Please check the muffler visually before every season. In principle the damping wool should be replaced every 2 years.
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Exhaust systems for 4-stroke engines are usually composed of 4 parts: a header tube, collector, link pipe and muffler or silencer. The configuration can vary widely depending on the engine design, the motorcycle frame and the intended use of the motorcycle. The design of the resonance exhaust systems for 2-stroke engines are very different from those for 4-stroke engines because of their different functioning and effects on the engine.
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There are two types of muffler: absorption and reflection. In the former, the exhaust gases travel through a perforated metal tube located inside the muffler’s outer sleeve. Damping material is placed between the outer sleeve and the perforated tube, which partially absorbs the passing gases, thereby reducing the noise emissions. The other method, reflection, works on the principle of damping chambers which extend or shorten the path of the exhaust gases through the muffler and thus reduce the noise emissions.
The primary function of the muffler is to muffle the sound, but its volume, shape and length also indirectly affect the engine power, the sound of the engine and the noise level of the exhaust system. Greater volume means more damping effect, but also greater physical size. Due to the physical imitations of mounting exhaust systems on motorcycles the best shape is an oval, which makes a good compromise between the volume and width of the muffler.
High-capacity engines require more noise reduction. In fulfilling this condition we have to make sure that we do not reduce the flow of the exhaust gases. Therefore we make use of the dual-muffler solution. And of course we always have to take into consideration the damping material – damping wool which has to be extremely resistant to high temperatures (they differ depending on the type of engine – more or fewer cylinders), as light as possible and have exceptional damping capacity.
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It can, but, conversely, more noise does not guarantee higher performance. This is particularly true of three-, four- and five-cylinder engines. The trend in MotoGP for megaphones instead of conventional mufflers is a case in point. Megaphones are extremely loud but the power difference compared to normal racing mufflers is minimal. They are only used to give a heightened atmosphere for spectators and to save weight.
Single and twin-cylinder engines are a different story. For these, it is very hard to find the best compromise between noise level and optimum power. In order to keep noise to an acceptable level, we have to sacrifice mid-range power.
How often do I have to change the damping wool? Is it necessary at all?
Parts of exhaust systems: general description and difference between 4-stroke and 2-stroke exhausts.
The muffler: what is its function, why is it even necessary? Influences on design: volume, shape, length, damping element?
