Like I said, I could definently hear a difference in the engine when running with the exhaust under water and felt the small decrease in noise was not worth risking burning the valves on my nice Hondas, but I do appreciate the heads up Hoser.
Has anyone ever cut open the exaust muffler on one of them small honda generators that are extremely quiet and try to reproduce it for the larger engines? Just a thought. I'm gonna look into this low tone muffler and see if they make one for my hondas, or adapt it.