Abstract

To compete in the dynamic events at the the Formula SAE IC competition, each vehicle must undergo a rigorous technical inspection. One element of the inspection is the Noise Test, which states that each car must be quieter than 103 dBc when idling and less than 110 dBc at the engine redline. Over the past few years, WashU Racing has used off-the-shelf mufflers with a guess and check system to find muffler combinations that satisfy the noise requirement. The results of that method have yielded either heavy and performance damaging muffler configurations or mufflers that have failed to meet the sound requirement. Historically, they have struggled to be below the redline noise threshold.

The study detailed in this paper aims to design a custom muffler for WashU Racing to meet the Noise Test requirement while minimizing both weight and performance loss. Specifically, the muffler aimed to target the redline RPM, 11000. First, physical testing was performed to figure out which sound wave frequencies created the largest dBc peaks. Then, using Gamma Technologies' GT Suite software including GT Power, GEM3d, and GT Post, mufflers were iterated on to target the sound wave frequencies producing the greatest noise.%< --this sentence could be improved

The C-Weighted Total Pulsation SPL was used to measure the sound output. Muffler perforation holes were also studied to determine the optimal number of holes and the optimal hole size. The final design yielded a 16 inch long muffler with a 12 inch shell, two J-Pipe resonators, and perforations along the inner tube. The expected sound output of the vehicle at redline is 96.55 dBc, which will allow WashU Racing to pass the Noise Test.

Document Type

Final Report

Author's School

McKelvey School of Engineering

Author's Department

Mechanical Engineering and Materials Science

Class Name

Mechanical Engineering and Material Sciences Independent Study

Language

English (en)

Date of Submission

12-23-2025

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