Eli, a glasspack is a style of muffler popular in the 60's and 70's. It is bullet in shape and consisted of a straight-thru core surrounded by fiberglass wool-like packing. It would start out with a nice but loud mellow tone that would get progressively louder and raspier (more high frequency content) as the fiberglass blew out. They did give good hp gains over stock mufflers. They fell out of favor when the current chambered style mufflers and steel wool packed mufflers came onto the market.
