Chuck,

Where did you get your fuel consumption numbers? They are a bit on the
low side in my experience. The normal rule of thumb for gas engines,
which I've found to be pretty close, is 1 gph for every 10 hp. At 3400
RPM most engines, properly propped for the boat, will run at about 50%
of maximum rated power. That would put the 350MPI at 15 gph and the
496 HO at 21 or 22. I have neighbors with both engines and that's in
the ballpark for what they are seeing. My old 350 4bbl rated at 260 hp
has always burned right around 13 gph at 3400 cruise.