alpha 1 gen 2, 3.0 outdrive on 4.3

[wilepine]

I have a mercruiser 4.3 engine and no compatible outdrive for the boat. However, I do have an alpha 1 gen 2, 3.0 outdrive. I know the gears are different in a 3.0 and a 4.3.

Can I put he 3.0 outdrive on the 4.3 engine and what pitch would I need to re-prop to?

 

[Scott Danforth]

first, welcome aboard

is the boat a gen 1 or gen 2? you dont give the required specifics

assuming both post 1991. you want to put a 1.94:1 drive behind a 1.81:1 application?

you will go up in pitch. you will have to test. however a simple ratio will get you close.

without weight of boat, hull, etc, we can not answer your question with the limited information provided.

 

[Scott06]

I have a mercruiser 4.3 engine and no compatible outdrive for the boat. However, I do have an alpha 1 gen 2, 3.0 outdrive. I know the gears are different in a 3.0 and a 4.3.

Can I put he 3.0 outdrive on the 4.3 engine and what pitch would I need to re-prop to?

What size boat is it in?

If, if the boat had acceptable performance with say a 17" or 19" prop, then you could step up to a 19" or 21" and it would probably work just fine.

If it is a smaller boat, like two of my neighbors have (tahoe Q5) w a 4.3 and a 1.81 drive that needs a 23" to keep rpms down then I think you would run out of prop pitches. If a bigger boat that is underpowered and would need a 17" pitch prop then going up in ratio wouldn't hurt.

 

[briangcc]

What 4.3 is this exactly?

I ask as mine has a 1.6x ratio drive from the factory. Depending on the application you may be going too far to correct with prop pitch.

 

[wilepine]

first, welcome aboard

is the boat a gen 1 or gen 2? you dont give the required specifics

assuming both post 1991. you want to put a 1.94:1 drive behind a 1.81:1 application?

you will go up in pitch. you will have to test. however a simple ratio will get you close.

without weight of boat, hull, etc, we can not answer your question with the limited information provided.

Scott, thank you and I do apologize. This is my 1st post.

The boat is a gen 2, the 1.94.1 drive leg came off a 2005 bayliner 175 with a 3.0 engine. The boat I want to put it on is a 2006 searay 185 sport with a 4.3 engine.

You are spot on, i would like to put the 1.94:1 drive behind a 1.81:1

The weight of the boat is approximately 2400lbs with a fiberglass hull.

 

[wilepine]

What size boat is it in?

If, if the boat had acceptable performance with say a 17" or 19" prop, then you could step up to a 19" or 21" and it would probably work just fine.

If it is a smaller boat, like two of my neighbors have (tahoe Q5) w a 4.3 and a 1.81 drive that needs a 23" to keep rpms down then I think you would run out of prop pitches. If a bigger boat that is underpowered and would need a 17" pitch prop then going up in ratio wouldn't hurt.

Scott,
The boat I want to put it on is a 2006 searay 185 sport that weighs approximately 2400lbs with a fiberglass hull. The boat worked fine with the prop it had on prior. I have to check and see which size prop was on there.

 

[Scott06]

Scott,
The boat I want to put it on is a 2006 searay 185 sport that weighs approximately 2400lbs with a fiberglass hull. The boat worked fine with the prop it had on prior. I have to check and see which size prop was on there.

If you look in sea rays owners resources you will find the following info - for prop chart https://owners-resources.searayweb..../2006 Sport Boat Sport Cruiser Prop Chart.pdf

If yours is 190 hp carb vs the 220 hp mpi - and came with a 1.81 with a 23" prop, so in this case I would not go up to a 1.94 drive as you will run out of available prop pitches.




BTW here Sea Ray has links to these resources including a parts manual for the boat (not drivetrain)

Sea Ray - Owners

Join the Sea Ray Owner's Club for digital catalogs, downloadable boat documents and exciting content. Find warranty information and how to transfer ownership.

www.searay.com

 

[wilepine]

If you look in sea rays owners resources you will find the following info - for prop chart https://owners-resources.searayweb.com/propeller-charts-files/2006 Sport Boat Sport Cruiser Prop Chart.pdf

If yours is 190 hp carb vs the 220 hp mpi - and came with a 1.81 with a 23" prop, so in this case I would not go up to a 1.94 drive as you will run out of available prop pitches.

View attachment 373643


BTW here Sea Ray has links to these resources including a parts manual for the boat (not drivetrain)

Sea Ray - Owners

Join the Sea Ray Owner's Club for digital catalogs, downloadable boat documents and exciting content. Find warranty information and how to transfer ownership.

www.searay.com

Scott,
That you for posting this. Mine is the 190 hp carb, therefore, i will have to get the correct drive or rebuild it. Thanks again, extremely helpful.

 

[QBhoy]

Hi. There are a few boats like this where the 3.0 and 4.3 ratios aren’t too far off each other (in some cases). Given the info above I’ve read makes sense of my thoughts.
If I was to take a guess as a starter…I’d be going for a loan of a 23” to see what’s what.
I think you’ll be fine doing what you want to do with the drive available. Probably find that the 23” may be on the verge of exceeding the recommended rpms, but not by too much. You also have the safety net of being able to go more pitch if you need to. Plenty of options on props around the 23-25” size. I’d be almost sure you wouldn’t need any more than a 25”…if you did at all.
The closest 2 examples I can think of first hand, is a Monterey 180 bowrider that had a 4.3 carb 190hp mated to a 1.81 alpha. I put a 23” black max 3 blade on her. She would see just over the recommended rpms and nearly or around 50 mph from memory. She had a stepped and fairly quick hull on her. Could likely have ran more pitch or a stainless 23” to best effect, if the owner was fussy.
Other was a much newer 19ft cuddy with a 4.3 mpi and a presumed 1.81 ratio. She ran a 23” laser 2 up to the limiter (if light) around 4900-4950 rpms and saw just over or around the 50 mph mark.
Just going by the given examples above…and I’d assume your searay is probably heavier (and likely less slick in the hull) than the Monterey at least…even with your proposed 1.9 odd ratio…you won’t be far off with a 23”…and certainly a 25” is an option to have available if need be. Hope that helps

 

[nola mike]

Did I miss what prop is on the 4.3 with the 1.81? The 1.98 will need 2-4" pitch increase.