Hello,

We purchased a 2001 Crownline 202
The boat has a Reman 5.7 MerCruiser with 4 barrel, with stock cylinder heads. The engine has 30 over flat top forged pistons, a new camshaft - specs are intake 270 Exh 274 duration @.050: 220 224 - valve lift intake and exhaust .474,,,, a new merCruiser crankshaft and a new MerCruiser intake Manifold and a holly four barrel carburetor.
The lower unit was not installed, and Boat did not come with a propeller. I installed the alpha one gen 2 drive - Gear ratio, 1.62 R

The boat is right at 4100 pounds loaded.
The engine rev limiter is 5000 RPM

We took the boat out with a 21P 14” 1/4 three blade stainless steel prop.

The engine blows through the prop coming out of the hole - cavitation, and the engine over rev’s with trim full down and full throttle coming out of the hole. It blows through the prop, wherever the trim is set when it’s trying to get out of the hole at full throttle.

If we go half throttle, it will eventually get out of the hole and come up on plane and get a Max speed of 46mph at full throttle.


The questions?

1. Should we move up to a 23P ?
2. Get a larger diameter and stay with 21p?
3. Move to a four or five blade prop. 21P

Full trim down at wot is dangerous to you and passengers (can bow steer badly) and doesn’t tell you much orop wise.

At WOT , max speed, and trimmed for max speed, what are your rpms ?

Edit in: Oh, you have a rev limiter you said. Factory one on TBolt V ignition or different one ?

Oh #2 - what valvesprings and what rates did you install on those stock heads for that cam ?

With a 1.62:1 ratio, I would definitely go to a 23" pitch Mirage Plus or a 22" Rev 4...hopefully you have a prop shop/marina that will allow 'try before you buy' on props.
You're probably making between 270 - 300 hp at the crank. You have a fairly heavy boat to get moving. A 4 blade like a Rev 4 will be your friend there.
I don't know much about the anti-cavitation plate clearance on the Gen II Alpha 1, but I suspect it won't let more than a 14.75" prop swing? SO you are going to have to use pitch to soak up that power.
Curious why you didn't go 1.50:1 on the outdrive ratio?

2001 will have vortec heads. With that cam, if carb and ign timing correct i’d say 330-350hp at somewhere near 5300-5400 rpm. Damn rev limiters

1. WOT - trimmed for max speed 5000 RPM bouncing the limiter.
46 MPH

2. It has an MSD marine ignition system.

3. The valve springs on stock vortec cylinder heads work great with this camshaft.


4. We bought the boat with the outdrive removed, the last owner did not put the outdrive back on, the 1.62 came with the purchase of the boat so that’s what we used.

5. Yes, there is more RPM there we set it for 5k to start.