The discussion centers on the sources of engine noise, particularly the sounds produced during operation. Key contributors to engine noise include combustion noise, exhaust gases, and the shockwaves created by expanding gases when the exhaust valve opens. The participants clarify that while combustion noise is significant, the repetitive "kicking" sound often associated with engines is primarily due to exhaust pressure pulses. Differences in engine types, such as air-cooled versus liquid-cooled engines, affect the audibility of these sounds, with air-cooled engines producing more distinct noise from combustion. Overall, the complexity of engine sounds is influenced by various factors, including engine design and exhaust systems.
