Changing outdrives,need to know what prop pitch change is needed

[617bsman]

Changing outdrive's with a overall gear ratio of 1.68:1, to one with a 1.86:1 ratio, how much of a prop diameter and/or pitch change should I have to make.
The boat is a omc sunbird 175 Corsica with a 4.3l 2 barrel carb.

 

[HT32BSX115]

Re: Changing outdrives,need to know what prop pitch change is needed

Howdy,

It's doable for the most part.

Most people would need to know what the prop pitch, WOT RPM and speed is with the current drive and prop....

Then you could go to a prop slip calculator to get in the ball-park.....

Prop Slip Calculator

For example,

a 1.68 drive with a 19p prop (with about 15% slip) would produce around 42 mph at 4600.

the same engine with a 1.86 ratio and a 21p prop would produce approx the same speed....

 

[617bsman]

Re: Changing outdrives,need to know what prop pitch change is needed

Thank you for your response

The example that was given is correct for my boat, with changing outdrives and going to a 21 pitch prop, will I have about the same hole shot for pulling a skier up out of the water.