bunky1957

Out of curiosity I've been trying different props on my 1989 Formula 311 ,a heavy deep v with bravo drives . Old style Mirage (not plus) 25 pitch will run 68 mph at 4800 rpm. Slip is 12%.Cruise 39mph @ 3000. Excellent holeshot, no ventilation. Motors make max power at 4600 rpm so I'm looking to get the rpm down. New Mirage 27 Plus runs 65 mph at 4600 (Mirage 25 will do same).Slip is 17%. Why so much? Cruise is 41 mph at 3000 rpm.Poor holeshot, lots of ventilation,props break loose easy, even on plane. Boat doesn't feel good with the 27's I would expect the newer 27 Plus prop with additional cup to better the older 25 Mirage's numbers. Then I put on a pair of old style 29 Mirage(not plus). 65 mph at 4000 rpm. 11% slip. Cruise is 45 mph at 3000 rpms. But so much ventilation out of the hole I could barely get on plane. Blade area on the 27 Plus looks alot smaller than blade area on the old 25 mirage. Anybody care to chime in with a theory on why the 27 Mirage plus does poorly?

Griff

What engines do you have that make max power at 4600rpms???? 330's???? They are fine to spin to 4800rpms.

If all you want to do is cut rpm by 200, then switch from the regular 25 Mirage to 25 Mirage Plus's. That will cut 200rpms and the top speed should stay the same.