triton sf-18 with 150 merc xr6, can i go from a powertch 21 pitch 4 blade to a Mark 7 17 pitch 4 blade off a merc 175??
What RPM are you turning at WOT with the 21-inch prop? We'd expect that to increase by somewhere between 650 and 800 RPM if you dropped down to the 17-inch wheel!
We need more info as to your goals and the status quo.