94 Z220 Prop Question

juttmk · 10-06-2017, 02:45 AM

94 Z220
7.4L
Bravo 1 1.50 ratio
19 pitch Mirage Plus (No Plugs)
SX trim tabs
Corsa Captains call exhaust
28 gallon of fuel
400lb passenger weight
500lb cargo

Just installed freshly rebuilt engine back in May. Spent most of the summer properly breaking in the engine. Now that the engine is broke in I'm trying to figure out why my top speed is so low. The timing is correct and RPM's have been verified on the timing lights rpm function.
4800 rpm
1/2 trim
40 mph

One of my solenoid for the dumps went out and the boat would not even get on plane due to the cavitation that was occurring with no plugs in the props ventilation system. Could the force of water through the prop be causing the high prop slippage(35%)? What would be the best option for a prop that would give decent hole shot and top speed? Should I start with plugging off the props ventilation ports?

**Scottie1961** · 10-06-2017, 03:53 AM

Take my comment with a grain of salt as my experience with those vents is on an outboard. I had a center console fishing rig and heard the vents helped the prop to spin up very quickly which is critical in shallow water starts. I don't think the vents affect the prop slip once up on plane. At least that is my understanding. I would plug the holes anyway and see if that makes a difference. Just a shot in the dark but have you checked the prop hub? Could you be getting some spin which would rob you of some power. Usually they just spin out but who knows?