trouble phil nothing else in 4" is available for a muffler, unless you go a twin system with chambered insides and dual outlets and that just wouldn't do. the whole system is on v-band clamps so if the need arises to go with something else its an easy fix. im a little worried how loud its going to be, but that's second to building something that is going to offer no power restriction once the engine is pushed. for street duties, well, ill worry about that later!