Modifying and improving: "Sports exhaust silencers"

The basic job of a silencer in an exhaust is to dissipate the sound waves coming from the engine.

In the UK and America where early cars had poor silencers we have a culture that associates noise with power. In Japan where engines were introduced with silencers the accepted exhaust note is very quiet and more of a buzz.

Are silencers really necessary? The noise an engine generates is phenomenally loud and most of this exits the engine via the exhaust. The noise is too great to be comfortable when driving and is a nuisance to everyone else around. For this reason then most countries have legislation requiring a silencer to be fitted to the exhaust.

Most silencers around contain some kind of sound deadening material to absorb the sound waves but exhausts work in different ways.

There are 2 primary exhaust types one contains a series of baffles and this reduces the exhaust flow as well as reducing the noise emitted.

The second type is a straight through pipe with perforations in it. The perforations take the sound energy and as this bounces back of the outside of the silencer it distorts and reduces the sound waves in the main exhaust charge cancelling them out.

Some manufactures have a primary and secondary resonating chamber to break up the sound and these can be of one or both types outlined above.

In a performance engine you really want the exhaust gases to be emitted as quickly as possible. The baffle type of exhaust is too restrictive in this instance so we would need to look to a straight through exhaust back box.

The benefits of the perforated pipe are obvious. The main exhaust stream is allowed to continue virtually unimpeded and the holes primarily allow the sound waves to penetrate and be absorbed.

The overall bore size of the entire exhaust system has an optimum setting. To small and it is restrictive, too large and the exhausts will flow more slowly. A larger bore silencer will not affect the airflow by a noticeable amount, and the larger the silencer the deeper the sound.

If you are performance tuning your engine, you need to choose a silencer that does not restrict the engine. A silencer alone will not add power to an engine but a restrictive silencer will rob you of power.

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