If you are hitting 4800 rpm with a 21" pitched prop then i'd say you are just about perfect. You could gain maybe 1 - 2mph with a slight sacrifice in low end acceleration by increasing to a 23" pitch and that would drop your rpm max to about 4600 but....i dont think it's worth it. Just my 2 pennies worth. :)

Try this link, It's Mercurys prop selector:

https://appcenter.mercurymarine.com/...lector/home.do

Re: Proper Prop Specs?
 

I have a 3.0L on a 180 Diablo that came with a 14.5 x 17 prop. The WOT speed was about 38 MPH at 5000 RPM. From some research the approach for the proper pitch was one inch of pitch = 200 rpm. So I went with a 14.5 x 19 prop for some performance and proper rpm. Well the speed increased to 42 mph but the rpm remained the same at 5000 rpm. Should I consider this rpm situation a gage problem?

Re: Proper Prop Specs?
 

The max rpm for the 3.0L motor should be in the neighbourhood of 4800 rpm. Either your tach is off, or you are still underpropped and you're hitting the rev limiter.

Re: Proper Prop Specs?
 

You can check your tach to see if it is set at '4 cyl'. On the backside there is a small dial marked 4 - 6 - 8 etc. Just spin the dial a few times & set it at '4'. Sometimes this will correct a tach problem. If you are still hitting 5000rpm at WOT then yes, try a 21" pitch.

Re: Proper Prop Specs?
 

Can anyone do a "how to" post with pictures on how to change a prop? I have done some reading up on the subject but unsure of what some of them are talking about without actually putting a picture to it. And also a list of tools and lube and such needed.

Well hopefully someone will be needing to change their prop soon haha if you do help would be appriciated. Thanks.

Re: Proper Prop Specs?