Prop advice for Starcraft holidayI

[jim martin]

Looking for input on Prop size I have a Mercruiser 140 on a Starcraft holiday 18 foot inboard I'm running a Michigan wheel 19 pitch prop and I was curious what kind of performance Improvement would I get to Stepping it up to a 21 or maybe a 23. I'm assuming the higher pitch I get the slower takeoffs it'll be but I was wondering how much high-end will be added

 

[Alumarine]

Maybe less high end.
You need to use a prop that will let the motor rev in the proper WOT range of 4200 - 4600 rpm with your normal load.
What are your rev's with the current prop?

 

[jim martin]

it will easily over rev to 5000 plus

 

[jim martin]

i try to go 4500 at the most for short bursts but cruise at 35 to 38

 

[Alumarine]

Are you sure both the tach and speedo are accurate?

 

[jim martin]

Sorry that was misleading I don't know the speed that I'm going exactly but I cruise at 35 3800 RPM. I have the feeling that my prop is too light in Pitch but I'm curious as to speed increase if I step up to a 21 or 23

 

[Alumarine]

You need an accurate tach and accurate speed to determine the correct prop.
The GPS function on a phone works well for speed.

 

[Watermann]

At 5k RPMs that 4 banger would sound like it's ready to come apart. There's no way a 140 would turn a 23p prop, you'd loose speed, wallow out of the hole and lug the motor. What make and model is you current prop? Many new props even aluminum ones have performance features that will eat RPMs due to substantial cupping and they have an aggressive rake where older props that on 4 cyl motors are dog eared with little to no cupping.

 

[jim martin]

I purchased a new Michigan wheel 19 pitch prop aluminum. I guess I had to find some sort of clip-on tachometer to see what's going on with the engine

 

[Watermann]

Ok, let us know how it works out for you. I would've recommended a Quicksilver Black Diamond.