Several sites out there to help you on this..14.5 to 15 1/8th isn't too much of a change. You need to make sure you have enough clearance between your blade and cavitation plate. Bigger Diameter doesn't mean more power or top end speed.. Best bet is to get with a dealer, head to the local lake and have them prop it for you.. Once you know the WOT for the engine you can try a few different props. It'll probably cost you about an hours worth of labot (plus the prop price) but this will help you get the best performance out of your rig.