are they just mufflers with fiberglass in them? what differentiates them from regular mufflers?

 

Glasspacks consist of a straight through perforated center tube and an exterior tube with fiberglass fibers in between.

A typical OEM muffler uses more strategies to remove noise than just absorption. The flow generally will not be straight through, and it'll be designed to have the different sound frequencies bounce around inside the muffler and cancel each other out to a much larger degree than with a simple glasspack.

 

^Yeah. A loud ass straight through muffler........................like he said. They have been known to actually lose power for applications in some 4 cylinder vehicles.

 

i've heard twin 18" glasspacks on a 1.5L toyota and it sounds great...not ricey at all. considering it for the accent.

 

Glasspacks tend to eliminate higher frequencies while resonators tend to eliminate lower frequencies. Usually you expect higher freqs from a 4 cyl. Also, it takes some tuning to get it just right.

My 30" glasspack changes pitch between 2-3000 rpm and the transition is kinda rough. I may eventually add a resonator to take care of that. Other then that my glasspack sounds great.