Who knows what prop

[David Carrera]

Does anyone have a 1986 4.3 OMC ? I'M TRYING TO SWITCH FROM THE 4 BLADE PROP THat WAS ON THE BOAT WHEN I BOUGHT IT. TO A 3 BLADE PROP , so I can achieve my maximum speed.MY PROBLEM IS, SINCE I DON'T ALREADY HAVE A 3 BLADE PROP MY RPMS AT WOT are from a 4 blade prop. WHICH MAKES IT HARD FOR ME TO DECIDE ON THE DIAMETER AND PITCH PROP I WANT TO GET. THERE WAS A CHART ON PIRRANA PROPS. I PLUGGED IN SOME FALSE NUMBERS USING THE 205 HPR AND THE MAXIMUM WOT SPECIFIED IN THE MANUEL OF 4200-4600 AND A MAXIMUM SPEED OF 50 MPH. THE CHART SAID I SHOULD RUN A 14x21. Does this sound right ? IF ANYONE HAS THE ANSWER OR MOTOR PLEASE LET ME KNOW.
THANKS

 

[steelespike]

Re: Who knows what prop

You should read the stickys at the top of the page and get us as much info as possible.
The diameter is a product of the design and a secondary consideration it may vary with the pitch.
An 86 4.3 appears to be a 185.If you give us your present prop size and max rpm abd speed we should be able to at least tell if your setup is working.Also wouldn't hurt to tell us what boat? Try to answer all the points in the stickys.Working from your present numbers should be more accurate than guessing on a prop chart formula.