Whats going to happen?

[mikesnowman]

Here is the Boat 96 Mariah Z200 LTD 5.7 2 barrel carb alpha one with 1.65 ratio I/O. Dry weights is 2550 pounds.
Currently does 50 mph( gps) at 5000 rpms. The prop is a MW Rapture 19 Stainless Steel, rebuilt.
I picked up a cheap Rubex HR-4 21 pitch. I have not even seen the boat yet, but am hoping to not lose much hole shop and pick up lots of top end.
Did I screw up?
Thanks

 

[45Auto]

Re: Whats going to happen?

I wouldn't exactly say you screwed up, having an extra prop (and tools to change it) should be a requirement on a boat anyway.

There won't be much, if any, difference in top speed. You're definitely NOT going to pick up "lots of top speed". The engine will probably wind out to 50 MPH at 4800 RPM with the 21" pitch prop instead of 50 MPH at 5000 RPM with the 19" pitch prop.

 

[steelespike]

Re: Whats going to happen?

Speaking in generalities Buying a prop before even running the boat through some tests isn't a great idea. When you change brands and number of blades it becomes more unpredictable.
I know nothing about the hr4 but will assume it is a 4 blade.
It may actually improve hole shot if the increase in pitch doesn't steal it away.
If 5,000 is your max rated rpm you will likely lose 2-400 rpm putting you below
your rated rpm. If its presently over then that will be better.Rated rpm is usually on the a label on the motor.The 4 blade may limit any possible increase in speed.
It will generally plane easier and stay on plane at less power assuming the 2" increase in pitch doesn't lower the rpm too much. Shoulkd have better no wake speed control.When you have a boat that will do 50 a prop change isn't likely to do much for top end.I hope you have good luck with it and props are unpredictable enough that I could be all wrong.

 

[mikesnowman]

Re: Whats going to happen?

I should add that the recomended rpm range is 4600 rpms I believe.