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It is common practice among young vehicle owners to modify the exhaust system of their vehicle to reduce exhaust backpressure with the perception that the output power increases. In the process of backpressure reduction, the output noise (Whakapau) of the vehicle also increases correspondingly. The conflict of interest that arises from modified vehicle exhaust systems and the general public is well publicised. This prototype was designed to meet the demands of exhaust back pressure reduction while at the same time mitigate the sound output of the vehicle. The design involves lining a cylindrical pipe with common glass marbles which is normally used for playing. The marbles are made of a sustainable material as it does not erode when exposed to exhaust gases and it is easily recycled. The prototype muffler is much smaller in size when compared to conventional mufflers. All tests were done in a simulated controlled environment and data collated using approved New Zealand Transport Agency testing regime. It has to be noted that the test focus was noise mitigation and not comprehensive engine performance testing. The results of the test prove a reduction of sound levels, however more testing needs to be undertaken with varying annulus depth, marble sizes and arrangements and engine loads.

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Singh, N. (2017). A Method of Sound Wave Diffusion in Motor Vehicle Exhaust Systems. Unitec ePress Occasional and Discussion Paper Series (2017:1).

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Unitec ePress periodically publishes occasional and discussion papers that discuss current and ongoing research authored by members of staff and their research associates. All papers are blind reviewed. For more papers in this series please visit:

  • Date of Publication: 10.4.2017
  • Author: N Singh
  • ISSN 2324-3635