Glasspacks are not chambered mufflers like flowmasters. A glasspack is a cylindrical muffler, straight through design, with holes or sometimes louvers in the tube. There is a combination of fiberglass and what appears to be steel wool wrapped around the tube in between the tube and the cylindrical casing. They sound like pissed off bumble bees on 4 cyclinders, same sound but deeper on v6's, and they are really loud on v8's. You get alot of internal resonance. The sound is not controlled. It pops when you let off the accelerator. Its diffrent. Depends if you like that kind of sound or not not. Around my area, the "country boys" like to put them on their trucks. Personaly I dont like them, you can have loud, with a controlled deep growl. Flowmaster 40 series, super 40, super 44.