Two seasons ago, I bought a new 4-bladed prop. I could turn Wide Open Throttle (WOT) at 54-5500 rpms. Running around down in the lower end of the Chesapeake it's a law of nature you will run your prop into sand. Including me. I would estimate there's probably 1/16th of an inch that I've "polished" off each of my blades from getting stuck in sand. I checked WOT last wknd was only able to turn 50-5100 rpms. Engine has been running smoothly, no ignition or fuel supply probs. So why in the hell am I turning a lower rpm with a smaller prop? Fuel economy seems good, no excessive smoke, quick starts etc, just a low(er) top end. Places to look??? Leave it alone as long as the engine runs smoothly? I don't ever run at top end on a cruise, and the only time I do is to check engine performance. Thanks in advance.
Mysterious Top End RPM Issue
- Thread starter hotajax
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Since normally aspirated motors will lose 200 RPMs or more in hot weather and the fact that your bottom is now covered with growth ... I'm not surprised 1 bit you've seen a drop in WOT turns. I'll see the drop due to hot weather, but I scrub the bottom whilst at the beach, so I don't see that large slowdown.
Doc Stressor
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You likely bent the blades and increased the pitch if you ran sand often enough to wear off the tips of the blades.
You best replace your prop since you engine is being overloaded.
You best replace your prop since you engine is being overloaded.
Could also be quality of fuel, weight on boat, trim position, running with or against current, etc.
Call the guys at propgods.com. They are amazing when it comes to diagnosing and fixing prop problems. I have no affiliation with them but they worked magic for me on my boat.