2008 DF-90 Question

[spitzerone]

I am trying to find out the maximum rpm's for my engine for prop selection purposes. I am pegging at 5150 with my current aluminum prop at 34-35 mph. I want to increase speed (and hopefully fuel economy as well) by being able to get to the the max rpm. I am currently running an aluminum 3x14x19 that was installed on the engine by the dealer. I want to go with a stainless steel. So I am looking for answers for both max RPM and proper SS prop pitch.

[boats.net]

4500-5500 rpm's is range. Using a 17 pitch SS prop should give you about same rpm's as you are getting now.

[spitzerone]

I forgot to mention what is on the motor now. I have a 3x14x19 alum prop. I am wondering if I dropped to a 15 pitch if this would get me to the 5500 max rpm. Comments? Does the pitch need change from alum to ss?

[boats.net]

Dropping prop pitch will be about 150 rpm's per one inch of pitch increase in rpm's. Smaller pitch will give it more rpm's and better fuel economy but less top speed.

[Moonlighter]

I forgot to mention what is on the motor now. I have a 3x14x19 alum prop. I am wondering if I dropped to a 15 pitch if this would get me to the 5500 max rpm. Comments? Does the pitch need change from alum to ss?

A 17" prop should get you close to max rpm. 15 will probably be too low. As noted above every inch typically gets about 150rpm. So 2 inches : 300rpm. Currently 5150 + 300 = 5450.