[THEFERMANATOR]

Originally Posted by garbubba

I'm at a loss here....

13.75x17 ss prop, 13 7/8x15 aluminum prop, 13.75x13 ss prop

You say all three of these props gave you the same RPM's at WOT? Comments about aluminum being different than SS notwithstanding the two stainless props are 4 inches of pitch different, they should give you way different RPM's at speed.


The tach sure seems suspect, if not something is surely wrong.

Not always. 15 pitch doesn't equal x rpm and y speed for every prop. Some basic props can run say 5200 in a 17 pitch at 45 mph while a different style 13 pitch could turn the same 5200 at 42 or 43. Pitch is just one meadurement when it comes to props. Some props also have what we refer to as progressive pitch where the pitch varies across the blade, or you can have one with alot of cup in it, larger diameter, different hub, and so on.