Induction noise has become a major source of consumer complaints in automobiles powered by four-cylinder engines. Induction noise typically manifests itself as a low frequency booming or “mooing.” It is most noticeable and objectionable under wide open throttle, hard acceleration conditions. In an effort to understand the basic causes of this noise, so that potential remedies might be more intelligently applied, an extensive study was undertaken. Careful measurements were made on a four-cylinder, motored engine. Dynamic pressure variations within the induction system, and external to the engine were studied. Peak to peak pressure variations of over 2 psi were found in the intake runners at the valves. Evidence of nonlinear acoustic behavior was found. A detailed examination of the events that cause induction noise is presented.

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