prop size

[ron_ny]

I have a 88 23' donzi ragazza w/5.7 alpha one. wondering what top speed and best prop size for this boat is. have a 15 1/2 19 pitch prop now and getting around 49mph now. Not sure about tach, only shows about 3000 rpm

 

[This_lil_fishy]

Re: prop size

Get your tach fixed. There is no way to know if you are running at the right WOT rpm without it, which also means that there's no way to tell which prop is best for your boat. That said, I'm betting that prop is way to small in pitch for your boat....and running WOT you're in danger of damaging your motor...but again..without a tach no one could say for sure. My 20' with 4.3 will over rev with the 21 pitch prop I have on it for instance (5200rpm to the rev limiter).

 

[wca_tim]

Re: prop size

Sounds like your prop is probably pretty close and your tach is off. I might try checking the little switch on the back of the tach, move it back and forth a few times and then make sure it is set on 8 cylinder...
or borrow a shop tack, or even a digital timing light with a tach function built in and run it to see how it reads.

(note to second poster. assuming you have standard 1,81 gear for a 4.3, there's on the order of 4-5" pitch equivelent difference in gear ratios for your boats. his 19 is more like a 23+ on your boat...)