omc 4.3 speed and rpm

[imarolltide]

i am new to the inboard boating world,i have just purchased an 89 sunbird eurosport 2 with an omc 4.3 engine with a cobra outdrive.i believe it is 18.5 feet long,it has a 19x13.5 prop(i am sure of the 19 but not the 13.5).i am tuning it up and was wandering what rpms i should expect(max,cruising),and top speed est.any help you guys can give would be appreciated.it has a 2bbl carb.

 

[Boatin Bob]

Re: omc 4.3 speed and rpm

If it's a 2 bbl then it's probably around 175 hp, the numbers for your prop sound reversed, first number is the diameter and 2nd is the pitch or angle of the blades, typically cobra's have 14 1/2 or 15 in diameter props and the pitch could be 15, 17, 19 typically. The top speed RPM's for your motor are 4200-4600, you want to be in this range so you need to take it and run it to see what kind of RPM's you are pulling going wide open. I would think that boat with the right prop should be getting in the mid to upper 40's for speed

 

[Liquid_force]

Re: omc 4.3 speed and rpm

I have the same engine and a slightly larger boat. The prop is a 14.5 x 19. It will run at about 4300 rpm and right around 40mph.

 

[imarolltide]

Re: omc 4.3 speed and rpm

thanks for the info.