Increasing demands on the capabilities of engine thermo-fluid dynamic simulation and the ability to accurately predict both performance and acoustics have led to the development of several approaches, ranging from fully 3D to simplified 1D models. The quasi-3D approach is proposed as a compromise between the time-demanding 3D CFD analysis and the fast 1D approach; it allows to model the acoustics of intake and exhaust system components, used in internal combustion engines, resorting to a 3D network of 0D cells. Due to its 3D nature, the model predicts high-order modes, improving the accuracy at high frequencies with respect to conventional plane-wave approaches. The conservation equations of mass and energy are solved at cell centers, whereas the momentum equation is applied to cell connections including specific source term to account for the of sound-absorbing materials and perforated elements. The quasi-3D approach has been validated by comparing the predicted transmission loss to measured data for a number of standard configurations typical of internal combustion engine exhaust systems: a reverse-flow chamber and series chambers with perforates and resistive material. 1. Introduction Internal combustion engines are the source of mechanical, combustion, and gas dynamic noise. In particular, gas dynamic or pulse noise is related to the unsteady flows in the intake and exhaust systems, induced by the cylinder gas exchange process [1]. The level and quality of noise radiated from the open ends can be controlled by different arrangements of pipe systems and silencers to achieve the required vehicle exterior and interior sound characteristics by attenuating or enhancing certain spectral components. Today numerical simulation codes are very useful during the design and optimization process of both intake and exhaust manifolds and mufflers to quickly define the best geometries which can be finally refined experimentally. The attenuation features of simple and complex acoustic filters can be predicted by 1D and 2D-3D fluid dynamic/acoustic simulation codes with different levels of complexity, both in the time and frequency domain. On one hand, 1D linear/nonlinear codes are nowadays widely used to calculate the acoustic performances of mufflers [2, 3]. Certainly 1D linear acoustic codes are mainly applied for this purpose [4–6] due to their simplicity, accuracy, and very short computational times. However, as the flow speed becomes not negligible and the sound pressure level of the signal reaches values of 160？dB, as it can happen inside a muffler for
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