Im looking for mufflers on my true dual 2.5" setup. I'm curious what the difference between them are physically, performancewise, and sonically. Which is quieter too?

 

A "turbo" muffler (1st used on Corvair Spyder turbo car, hence the name), is basically an oval case with two tubes in it, one the inlet that goes to the back of the case, the other the outlet that goes to the front of the case, with plates or baffles that go around the tubes with holes to allow the gases to flow through. The plates form 3 smaller chambers within the outer oval case. Designs vary from that, some using perferated tubes in the inner chamber, for instance. There isn't any defined design, however, so anyone can put "Turbo!" on their product and call it a turbo muffler.

Glass packs also vary, but the typical design is basically a perferated pipe with a larger tube around it to form the case, and the space between the tube & case is packed with fiberglass. They typically are pretty loud, and the muffling they do is accomplished by reducing the size of the pipe inside the muffler from the inlet/outlet size - they are also, therefore, typically more restrictive for the amount of noise they produce than "performance" mufflers should be.