350 MPI's no silent thunder at 60% throttle. Stock Iron manifolds also.

You are running stock tips? Did you do anything about water coming back into the exhaust? Are you still running with out the box?

Still no box. Just installed rubber flappers on the factory tips. I have not had any water make it up into the manifold. I have taken several big waves to the stern with just the rubber flapper tips, even one over the swim platform onto the back pad with no ill effect. It used to bother me but I no longer think about it. Take the box off, mine had delaminated a little bit and sounded awful getting up on plane like someone was slamming the swim ladder cover over and over.