HI guys,my boat is a 20 Spectra daycruiser that's quite heavy in the back sitting in the water.The waterline is above the exhaust tips but the risers keep reverson remote.If you put flappers at the tip it's even safer.I run ford motorsport's marine cam,493 intake lift 502 exhaust with 115 lobecenter.I've built a 460 for my friend's 19 spectra wich has ford's 443 cam with 563 intake lift 588 exhaust and 112 lobecenter.Same scenario;exhausts under waterline supertrapp muffler's and no problem with water reverson.