Prop for 1981 80 HP Mariner 4 cylinder engine

[Tacomaj]

Any one out there with experience on this engine to recommend the best pitch to use.

I currently am getting around 5000 rpm at WOT, fully trimmed. The prop I have now is not stamped with the pitch, therefore I am lost as to what to buy for it. Everything I can read points to a 15 pitch.

thanks Tacomaj