Hi Slapper, It is only slightly louder than stock. I was looking at also making the outlet bigger (for a bit more noise & hopefully performance) but this will take time & more Dyno runs to see how it is running (Tune). The current mod I do works very well (Is noticable difference over stock in performance, & Torque up to 10%) & have done Dyno's so we know it is running well. (Proven Product) In fact it was independly tested by Cycle Torque Magazine in Sydney, & the tester was so impressed he wanted one for himself. This mod was specifically designed for those who want to keep the bike quiet. Hope this answers your question. Chappy.