Baker-all you need to do is check out a prop calculator. If I take my boat and do the calculation as is, with continuous duty rated JD's, then change only the rating on the engine (raising HP and raising Max RPM to JD's max rating on our engines), there is no appreciable change in either the diameter (about 0.1") or pitch (about 0.3"). On a full displacement hull, this should not be surprising. It takes a calculated 209.5 HP to move our hull at hull speed, it does not matter whether that HP is produced by a 154 HP engine or a 225 HP engine (the lowest and highest ratings on our JDs). Since all else remained the same in the above, including the reduction ratio, it should take the same size prop at the same prop rpms to move the boat. One interesting note, the 209.5 HP is 72% of our HP available at the shaft. With the higher rated engine, the 209.5 HP is less than 50% of the HP available at the shaft-a lot of wasted power.