prop size

[adamkeith]

Hey Everyone, Ive got a 2001 Maxum 2500 SCR I bought in January and im looking to find the original prop size and pitch, my mechanic doesnt believe I have the original prop, RPMs top out about 3800, it had 21 pitch 3 blade when I bought it and have tried 19 pitch 4 blade and a 17 pitch 4 blade both helping it plane out but loosing top end speed and RPMs. Any insight will be appreciated. Its has 5.7 L fuel injected motor with Bravo 1 outdrive. Thanks Adam

[mmwjr]

Welcome aboard.

Going from a 21" pitch 3 blade to a 19" pitch 4 blade should help bottom end but that extra blade adds drag so top end will not change. Also if going from aluminum to SS will impact top end as the SS is much heavier.

What is the WOT for each prop? This engine should be 4400-4800 rpm.

[shrew]

WElcome aboard adamkeith!!!

You should only change one variable at a time. Decreasing pitch will increase max RPM. 1" pitch = 200 RPM.

However, increasing blades has the same effect as increasing pitch. So you dropped from a 21"P to a 19"P then increased from 3 blades to 4.

Yes, when you increase max rpm you will loose top-end. . At this point you need to get the engine running in the max. rpm range (4400 - 4800) as stated by Mike (above).

The goal should not be top-end speed. You bought a cruising boat.