Prop Question
 

Running a 89 Scarab 22. 350 Magnum, 1.47 gear ratio. WOT is 63MPH in the right water. Prop is 21P Laser II. RPM's at WOT is 4300. Any ideas for more Top speed? Maybe a 4 blade?

Actually, you may be able to drop a pitch size and gain some speed. RPMs seem a little low. I would think 5200 is more in the ballpark. If you get the engine up into the higher RPMs it might generate some more speed. (21p turning 4300 is not as fast as a 19 turning 5200) I'm also not a big Laser fan. Although I've had friends that liked them, I've never had much luck with them. On Mercrusiers (which I assume your's is) the rake and added blade area of the Mirage Plus props works well.
I wouldn't recommend a 4-blade in your situation unless cavitation is an issue. In surface drives and high X-dimension boats they're good, but they create a lot of drag when ran deep. If speed is the ultimate goal, a 3-blade is your best bet.