I run a 90 on my 16'x66" Koffler and it's just enough to push 3 guys around. I remember when you were mulling over what size motor to get, I said that the 90 was too small for that boat. I'm not getting any satisfaction by saying I was right, but am saying don't waste any more money by putting a stainless 4-blade impeller on that motor. Cut your losses and move on. Good luck.