We have done lots of muffler testing and I wanted to share why the Dynomax Super Turbo works as well as it does for sound level control, tone, and airflow/performance.
In Cutaway 1, you can see the basic three pass system it uses. Note the louvers are stabbed outwards. This way, there is nothing in the air flow path to swirl it as much as if they were stabbed inward. This is a 2.5" in and out muffler. The tubes are that large all the way through. No pinching or reducing.
In Cutaway 2, you can see their Flow Directors that do a nice job of reversing the flow direction. They are large and handle the gas flow heading into and out of them pretty well.
In Cutaway 3, you see me holding the glass fiber mat they use. It was chosen for its density and toughness against fracture and blow out and it does a good job at absorbing the high frequency hisses and spits and crackles.
Cutaway 4 shows that the mat is actually wrapped around the center three tubes and all can use it for sound control.
Cutaway 5 shows what the incoming gases see: not much restriction or reduction in pipe diameters all the way through.
The larger of these, the #17748 (HEMI sized) and #17749 big GM other GM A body sizes, work really well. The shorter ones, like this cutaway, are a tad louder and flow a bit less as the gases still get pretty turbulent inside.
NOTE, MOPAR uses offset in center out mufflers and the Super Turbo splits the Flow Director on the outlet side and runs the exhaust over and aorund the outlet pipe. This does impede flow somewhat but not as much as you would think, on typical moderately powered cars anyway.
Pypes now makes some like these too. The Dynomax patent expired on the Flow Directors and PYPES now uses them. Theirs also work pretty well.
These will not flow as much as a straight through muffler but they do a super job of sound control, noise level reduction, making a good growl but not too much, and minimal resonation. The little ones tend to resonate more than the large ones but all are pretty good at avoiding resonation. Large or small, they are far better at minimizing resonation as compared to chambered or baffled mufflers.