Loving mine sofar. It's quite a bit louder than the stock sj box I had in my ski before. Where it gets loud is when you are on plane it seems to resonate more with a helmet on, but once the exhaust is more below the waterline it quites down as you'd expect and it's still great sounding.
Does anyone have a video or audio of similar engines using OEM and JM boxes? I need a smaller than OEM box but want to minimize the increase the loudness. Has anyone used one of these (or another AM waterbox) with an inline silencer and water injection? Would it significantly help to quiet it down?