Establish Pipe Diameters
Firstly, establish the pipe diameters the muffler is to be attached to. The sizes in catalogues refer to the pipe size that the nipple tube on the muffler will accept.
Determine the length and cross-section of the muffler.
This is usually dictated by the length of the muffler being replaced or the available space under the vehicle.
What noise level and exhaust note is required?
The larger the volume (physical size) of the muffler the quieter the resultant noise.
For mufflers of equal volume, the smaller the flow tubes the quieter the resultant noise.
A general rule of thumb in the case of tri-flow design mufflers is, if the length of the muffler, the cross-section of the muffler and the nipple tube sizes are correct, then the muffler will suit the application.
For systems that are producing a "raspy" note with a tri-flow design, try using the equivalent size in a straight through glass pack or incorporate a glass pack in front of the main muffler, this will reduce the high-frequency note.
Where a deep note is required lean toward the glass packed designs.
For turbocharged vehicles, always lean towards the free-flowing designs as turbocharged engines are quieter than the normally aspirated ones and require less backpressure to perform at their best.
Use resonators in conjunction with the main mufflers when there is insufficient space or the noise level needs reducing on an existing system.
Glass packed resonators (hotdogs) will reduce the noise level by approximately 3-5dB and deepen the exhaust note.
Tuned or centre expansion resonators (no glass) will attack the noise frequency they are designed for but will also reduce the overall noise level by approx. 3-5dB.
Things to Note: