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The paper critically reviews the requirements for internal combustion reciprocating engines to meet present and future noise legislations according to their specific road vehicle applications. It reviews the significance of the vibration characteristics of structure elements in relation to the combustion systems employed and attempts to identify the importance of the balance between mechanical and combustion induced noise in engines falling into specific categories.

The paper classifies all current automotive engines into four distinct groups relative to engine usage and vehicle noise legislation. The noise characteristics of the engines in each group are widely different except that at their maximum rated speeds the overall noise levels approach the same value The sources of noise rank in different importance according to the size and type of engine. Therefore quiet engine design must also vary. The importance of mechanical noise is emphasised and it is considered that this source could be a limiting factor to future low noise engines.