Performance Exhaust Systems: Mufflers

by Mike Mavrigian

 

The purpose of a muffler is to aid in managing the engine’s exhaust sound level, and to “tune” exhaust tone. While some view the use of mufflers as simply a necessary evil, in terms of controlling engine exhaust noise level, mufflers provide an additional engine tuning aid in terms of horsepower and torque, primarily for street-driven vehicles that must operate and perform in a wide range of vehicle and engine speeds.

 

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For the sake of illustrative comparison, consider a firearm’s silencer. This device attaches to the gun-barrel exit in order to decrease the audible noise created by the explosive discharge. Contrary to the popular term, this device does not “silence” the discharge. Rather, it suppresses the noise, so the proper term for this device would be a suppressor, not a silencer. The same holds true for an automotive exhaust system’s muffler. Instead of silencing or eliminating the exhaust noise, the muffler suppresses the exhaust note. The design of the muffler has a direct effect on both the level of noise and the tone of the engine’s exhaust.

 

Round-profile canister, or bullet-style, mufflers offer both excellent straight-through flow and a reduced profile for exhaust routing where space is at a premium. (Photo Courtesy Borla Performance Industries)

 

Performance muffler designers invest an incredible amount of time in developing mufflers that reduce noise levels while providing minimal flow restriction. (Photo Courtesy Flowmaster)

 

The combustion process that takes place in the engine’s cylinders creates sound waves that travel from the cylinder head through the exhaust system. Along the way, these sound waves run through the muffler. Depending on the design of the muffler, these sound and pressure waves are altered by sound-absorbing insulation (such as fiberglass) or by interruptions as the waves interact by baffles and/or tubes that may feature perforations, any or all of which serve to cause the sound waves to lose energy. In a high-performance muffler, the objective is to alter these sound waves while minimizing flow resistance and backpressure.

Muffler designs vary from simple straight flow-through tubes with perforations where the sound waves are dampened by sound-absorbing matting that’s wrapped around the perforated tube, to designs that use a complex series of angled baffle walls and carefully designed internal tube bends that divert the waves while promoting both efficient and low-resistance flow and a specific noise level and “tone flavor.” Achieving efficient flow and developing a specific sound is a carefully orchestrated balancing act.

The total “recipe” of a muffler design, including internal volume of the muffler body, the thickness (or gauge) of metal, and the type and shape of internal baffling, can result in a range of sounds. The sound can be from quiet to throaty to raspy. The results can vary and can be tuned for different engine speed and load conditions.

The muffler sound, or exhaust note, varies widely depending on the style, size, design, and manufacturer. Generally speaking, it should come as no surprise that a muffler that features fewer exhaust path deviations, sound-absorbing chambers, and frequency-altering aspects produces a louder, or higher-decibel, exhaust note.

In addition to choosing a muffler based on low restriction, for a street application, you need to consider the type of sound that you desire. Apart from meeting acceptable decibel levels appropriate for street use, the muffler’s effect on engine exhaust note influences the buying decision for a particular muffler brand and style. Some drivers may prefer a quiet sound output at idle and cruising, and a throaty, louder note during acceleration, while others may prefer a louder, more notable sound at all engine RPM.

Without having the luxury of trying a variety of muffler designs, the only practical approach is to consider how the muffler manufacturer describes a muffler’s sound, listen to the exhaust sounds of vehicles and engines similar to yours at local car shows, and search vehicle-specific Internet forums for the opinions of others. As a result, you are better equipped to make your selection decision.

 

Mufflers with offset inlets are often needed for muffler locations to accommodate underbody or driveshaft clearances.

 

Some manufacturers offer direct-replacement mufflers; some offer mufflers specifically designed for power and sound enhancement for performance-minded applications, such as Borla, Corsa, Flowmaster, SuperTrapp, Spiral Turbo, and Magnaflow. Manufacturers such as these specialize in developing mufflers that maximize engine power while providing the preferred type of sound.

Keep in mind that a competition muffler’s requirements involve maximizing engine power while meeting a particular race sanctioning body’s sound decibel requirements, where applicable. For a street application, the design parameters are more restrictive. Performance muffler manufacturers must design mufflers that not only enhance power, but also provide the type of sound desired, while avoiding annoying droning or booming sounds that may be objectionable to the driver and passengers.

There is no such thing as the ideal muffler for every application because personal tastes vary. Some drivers prefer a raspy sound, while others prefer a low-frequency or “mellow” sound, while others may prefer a very quiet exhaust note at idle and cruising speed, with a notable increase in sound under hard acceleration. A muffler’s sound differs depending on the engine type, displacement, and powerband. With so many variables to consider, the reality in terms of selecting a muffler for a given application is to read each manufacturer’s descriptions of its models, and gather input from others who own vehicles similar to yours.

While the Internet is full of information both useful and false, vehicle-specific forums offer a good starting point to gauge the opinions of others who have tried a certain muffler brand and model with a specific vehicle and engine combination. Leading performance muffler manufacturers invest an extensive amount of research, development, and testing to provide just the right sound that various customers desire. Muffler technology is much more complicated than most people realize.

Although different-diameter pipe-to-muffler sizes can be adapted using step-up or step-down adapters (or by swedging a small neck to a larger diameter), it’s best to match diameters at all connections in order to maintain a constant diameter. Slip-together connections require a pipe OD to match the muffler ID neck.