I have a 1988 Baja 240 Sport with a rebuilt 454 bored to 468cu in with a roller valvetrain and Bravo 1 outdrive with 1.5 ratio. It came with a 3 blade Mirage 23 pitch prop. I have had it up to 64mph on GPS at 5000 rpm. Sometimes the prop will cavitate for no reason, I will be cruising along about 3000 rpm and the boat will drop and slow down. Any ideas what causes this? Any ideas about a new prop, what should I get? I have a quicksilver 23 pitch cleaver, it does not seem to change the performance any.

Cupping the prop more should help to stop the problem. Otherwise, a 4 blade prop will carry a load better.

sounds like your drive is to high try the drive all the way down if it stops then move drive up till cavitate then go a little . if you have it up to high it lose it grip

Get the prop cupped to Mirage Plus specs and then labbed to regain the lost rpms. Your rpm and speed is right on for about a 425hp engine.

Do you think I should get a 21 pitch prop?

No, get the 23 cupped and labbed. You should pick up a few mph and better bite.

Where do I get the 23 cupped and labbed?

blades 920 295 4435 would be close to you.