Mercruiser 4.3 Prop Question

[Chrislig]

I have a 2001 Rinker Captiva 192 with a 4.3 litre Mercruiser Alpha 1 Gen 2 outdrive. The previous owner installed a 4 blade stainless prop with a 19 pitch. At WOT, I can only get around 36 mph at 3800 rpm. The specs for this engine have max rpm at 4400-4800 rpm. Is it possible to get better performance with a 17 prop? I cant seem to find anything online for how this boat was configured from the factory.

 

[Bondo]

I have a 2001 Rinker Captiva 192 with a 4.3 litre Mercruiser Alpha 1 Gen 2 outdrive. The previous owner installed a 4 blade stainless prop with a 19 pitch. At WOT, I can only get around 36 mph at 3800 rpm. The specs for this engine have max rpm at 4400-4800 rpm. Is it possible to get better performance with a 17 prop? I cant seem to find anything online for how this boat was configured from the factory.

Ayuh,...... Welcome Aboard,.. Yes, a smaller prop will bring the rpms up,...
Are you sure the motor is putting out the power it should be,..??
What's the back story,..?? has it ever run the right rpms,..??

 

[jlh3rd]

eh, 3800 is lugging your engine. I'd be concerned with getting close to my max rpm @WOT. Then let performance be what it is.
Generally speaking, a 2" change lower will get around 400 rpm's higher, still under your recommended range.
and, yes, is the engine healthy?

 

[Scott Danforth]

Verify the drive ratio of 1.62:1
Verify all cylinders are firing
Verify the flappers are not laying in the bottom of the Y-pipe

 

[Renken2000Classic]

Maybe a dumb question, but are you trimming for the speed? That'll get you a few knots.

88 OMC Cobra, 4.3L. 14 1/2 x 19, 3-blade: 45mph all out, at about 4,500rpm. 2bbl carb.

Great (hole-shot?) also, btw.

 

[Chrislig]

Thank you for all the responses, much appreciated. The engine runs perfectly. Has all new fuel and ignition parts. If the boat is at idle and in gear and I punch the throttle, your in the water if your standing up so no issues there. The original brochure for the boat says 50 mph for a top speed. I'd be willing to take 40 - 45 factoring in the age of the engine but I always suspected the prop. I'll try the trimming suggestion as well.

 

[Chris1956]

I think the 50MPH claim is marketing.

My 18 foot SeaRay with a 4 bbl 4.3LX would get 42MPH, with a 21P prop. You will need to trim is to max, to achieve max speed.

 

[Scott06]

Thank you for all the responses, much appreciated. The engine runs perfectly. Has all new fuel and ignition parts. If the boat is at idle and in gear and I punch the throttle, your in the water if your standing up so no issues there. The original brochure for the boat says 50 mph for a top speed. I'd be willing to take 40 - 45 factoring in the age of the engine but I always suspected the prop. I'll try the trimming suggestion as well.

Also check the tach vs a shop tach. Would not think if you had soooo much pitch that wot was 3800 that you would have the great holeshot that you mentioned.
either rpms are off or there is a tune up issue have you verified timing both intial and total? and what do the plugs look like

 

[Renken2000Classic]

You will need to trim is to max, to achieve max speed.

Might want to clarify. If I did that the nose'd be pointing at the sky, lol. I must not be understanding.

I feed it in gradually until I get just a little bounce and then maybe back off a bit if it seems like it's going to worsen.

Throttling back, obviously requires trimming back down some.

 

[crazy charlie]

. If the boat is at idle and in gear and I punch the throttle, your in the water if your standing up so no issues there.

Incorrect statement.That IS an issue....if you are looking for top end speed.Your statement confirms that you have a prop that is a "pulling" prop.Low end torque /pull is for pulling tubes, water skiing, multiple occupants etc.A speed prop will do very little when you "punch the throttle".It will rev and sound like you are booking but will take some time to plane off and the moment the bow comes down and you do plane is when you feel the speed .Mercruiser liked to use 14 1/2 x 17 3 blade props .Should be a common aluminum prop for you to find used to give a try and see what that does for you. Hope I explained it well for you.Charlie

 

[Chrislig]

Thanks Charlie. Much appreciated.

 

[jimmbo]

If you want higher top end, ditch the 4 blade, and reprop with a 3 blade to attain the 4800rpm
What condition is the Engine in Mechanically, as in what are the Compression Test Numbers?