Design of a Reactive-Style Muffler for a Formula SAE Race Car

The noise generated by high-performance vehicles like Formula SAE (FSAE) race cars, presents a significant challenge in adhering to strict competition noise regulations. In this study two muffler designs were created: muffler design 1 and 2. Each design utilized two chambers to generate destructive interference, targeting two dominant exhaust frequencies of the Honda CBR600RR engine to maximize transmission loss and reduce sound pressure levels (SPL) below the FSAE-mandated range of 103 dBC at idle and 110 dBC at all other operating conditions. For each design, the exhaust noise and muffler performance were simulated using GT-Suite, allowing for an evaluation of noise attenuation across engine speeds. Experimental testing was conducted to validate the GT-Suite model and assess the effectiveness of muffler design 1. This testing involved measuring the SPL with a calibrated microphone, both with and without the designed muffler. Muffler design 1 was based on the dominant exhaust frequencies from the engine-out simulations while muffler design 2 was based on the engine-out experimental measurements. The simulation results showed all muffler designs were below the FSAE mandated SPL at idle and the high engine speed condition. The experimental testing showed that muffler design 1 was 7 dBC above the high engine speed FSAE mandated SPL. The experimental SPLs from engine-out and muffler design 1 were -6 to 1 dBC and 1 to 11 dBC above the idle and the high engine speed test values, respectively, from the simulations. Based on the comparison of the simulation and experimental results from engine-out and muffler design 1, the experimental SPLs were predicted to be below the FSAE requirement for muffler design 2. Therefore, muffler design 2, designed from the dominating experimental exhaust frequencies, achieved superior noise reduction compared to muffler design 1.