Join Date: Aug 2006
Location: Arlington, VA
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Yeah, lots of things can affect "registered" and actual rpm: dirty bottom, dirty prop, too much pitch or too big a prop, impaired engine (multiple reasons), etc.
BTW, travel lift guages are notoriously unreliable. Unless you've shipped a hell of a lot of stuff, I'd bet on the 22.5K plus gear.
So, too, are tach readings. But, if you've got the right prop for your boat, you should be seeing a lot more than 2200-2300 rpm for the 4-108 as a maximum.