[Zankan]

Hi!
I´m wondering wich kind of prop i shall use on my Z225?
I have a Mercruiser 5.0 liter with an Alpha one gen2 .

I have been told that the engine shouldnt go over 4400-4800rpm´s .
At this moment with the prop i have on it , at 23knots it lays on 4000rpms.

Anyone who knows? Ore knows how i can figure out what size and so on ?


best regards Robin
(sorry about my bad english)

[mikeyt]

hi Robin

Do you know what size prop is on your outdrive now? The 4400-4800rpm range is the maximum it should run at at WOT (wide open throttle). If you are running at 4000rpm at WOT then you can safely drop the pitch in your prop up to 3" assuming everything is good tune & she is running well otherwise. Each 2" drop in pitch will result in a 400 (approximate) increase in your rpms. This change though can be affected by prop design, number of blades etc so i would suggest that any change be no more than 2" for now. For example, if you are running a 21" pitch prop right now, you could easily drop to a 19" prop which will raise your rpms at WOT and in your case would also likely give you a extra 1-2mph in top end. That 4400-4800 range is where the engine operates most efficiently at WOT.

[Zankan]

Originally Posted by mikeyt

hi Robin

Do you know what size prop is on your outdrive now? The 4400-4800rpm range is the maximum it should run at at WOT (wide open throttle). If you are running at 4000rpm at WOT then you can safely drop the pitch in your prop up to 3" assuming everything is good tune & she is running well otherwise. Each 2" drop in pitch will result in a 400 (approximate) increase in your rpms. This change though can be affected by prop design, number of blades etc so i would suggest that any change be no more than 2" for now. For example, if you are running a 21" pitch prop right now, you could easily drop to a 19" prop which will raise your rpms at WOT and in your case would also likely give you a extra 1-2mph in top end. That 4400-4800 range is where the engine operates most efficiently at WOT.

hi! I think you missundestood me there.
My problem is that my engine has to high rpms at WOT .. Right now its 5200-5400rpm at WOT..
My prop is an 5 bladed 17" prop at the moment ..

Maybe an 3 bladed 19" prop shall sort my problems then ?

[mikeyt]

Originally Posted by Zankan

hi! I think you missundestood me there.
My problem is that my engine has to high rpms at WOT .. Right now its 5200-5400rpm at WOT..
My prop is an 5 bladed 17" prop at the moment ..

Maybe an 3 bladed 19" prop shall sort my problems then ?

Apparently i completely 'misunderstood' you. Yes, you need to change your prop to a 3 blade 19". That will drop your rpms by about 400 at WOT and should get you very close to the top end of the recommended range. It wont hurt to be able to hit 4900-5000 maximum but just dont run it at those rpms for any length of time.

[Zankan]

Originally Posted by mikeyt

Apparently i completely 'misunderstood' you. Yes, you need to change your prop to a 3 blade 19". That will drop your rpms by about 400 at WOT and should get you very close to the top end of the recommended range. It wont hurt to be able to hit 4900-5000 maximum but just dont run it at those rpms for any length of time.

Thanks for the help!
I just ordered a brand new prop , hopefully it will work out better with this one

best regards Robin