How high of RPM should my 140hp mercruiser run?

Question

My 140 hp 4cyl mercruiser engine on a 19ft open-bow at wot it will go to about 4100rpm at the most. Is that normal. The boat will do about 40mph.

Answer 1

Depending on whether the engine is new, used or refurbished, it would be best to consult the manufacturer. If some one has tampered with the engine on repair. If New, however, consult the manual.

Answer 2

Sounds pretty good.

Testing my memory the WOT should be between 4000-4400, so you are right in the range.

You may want to experiment with a different pitch, you have 300 more RPMS, maybe. However, I want to caution you, if you go strictly for top end with a 140 HP, you may lose so much hole-shot it won't be worth it.

How about going to a four blade or five blade to get your WOT right on 4400 and still have a good hole shot.

This repropping your boat can be a tedious process, and you will need an understanding marina to loan you the props. My thought: you have good top end, you're in the range for RPMs, keep your prop there.

Answer 3

for more speed and rpm use a three blade prop. for more thrust such as ski tow use four blade.(less speed less rpm).