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.
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Doug
87 Cuddy with a 94 Black Max 200!
& a 1983 Cuddy, looking for power.
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