Take it off. Blow an airhorn through it and then replace with street sweepers!
Just Kidding, but if you want my opinion a very loud and good looking set of pipes are the Samson Street Sweepers. If performance is an issue install baffles. I installed Big City Thunder, Monster Thunder baffles and those helped out tremendously on low end torque and they also took the edge off of the sound. I recommend making your own baffles with a 3/8 inch washer welded to a small piece of all thread instead of the overpriced Big City Thunders.
Good luck with the water heater!