I have a 1991 Johnson 115 2 stroke on my 17 ft center console. The prop that came on it has a pretty good ding in it. It is a steel prop. I could find no stamp on this thing for pitch size so I compared it to an old prop i have that is a 13x19. Pitch on the two look exactly the same. Measured the steel prop and it is 13.5 diamater. So I order a new aluminum prop 13.25 x 19. Thats 1/4 inch diff in the diamater but I fugure this should give me about the same rpm WOT. My engine is designed to run 4500-5500 WOT. Old steel prop was getting 5300 WOT, new aluminum prop 4000RPM WOT. I don't get it how can there be a 1300 RPM difference beteween these. The diamater should not have that much difference in RPM. The only other difference is the wieght of the prop, and i would think a lighter prop would swing faster. Any thoughts?
