Muffler Types & Expected Performance
Tri-flow or Reverse Flow Designs
These are the most commonly used design in both original equipment and aftermarket products. These designs will deliver 12 to 25 dB attenuation depending on flow tube diameter and the volume of the muffler. Work on the destructive interference principle. Those designs that incorporate fibreglass around the flow tubes will deliver a mellower and deeper note.
Glass Pack Mufflers
Glass Packs should not be considered as "just performance" mufflers. For years the glass packed muffler was the original equipment design used on many European vehicles. This design is making somewhat of a comeback in Australia.
Straight Through Design
This design delivers the best performance of all the Glass Packs. Usually manufactured using a mandrel bent perforated tube, the flow of exhaust gas is virtually unrestricted. They are exceptionally quiet for their design, delivering 10 to 20dB noise attenuation. The larger the muffler the quieter the resultant noise level, the density of the glass is also a factor as to how well this type of muffler performs. It will supply a deep note due to its ability to absorb high-frequency noise.
Centre Expansion Design
This design works on the same principle as the straight through design with the addition of an empty chamber in the middle of the muffler. The chamber acts as a Helmholtz tuner attacking low-frequency noise waves. It will deliver 10 to 15dB noise attenuation. They do not flow as well as the straight through design due to the turbulence created by the expansion chamber. They also come in a baffled version, where a baffle plate is situated in the centre chamber to further deflect noise waves. The baffled version is usually 3-5dB quieter but has a more restrictive flow.