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todens22

Propeller/RPM Question

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todens22

I have a Sportster with a 5.7 carb engine.  There is an ACME 515 prop installed on the boat now.  I brought the boat up to wide open throttle last night and noticed that the tachometer reached 5,000 RPM.  Backed off right away. I checked the specs in the book and it states the WOT range should be between 4400 - 4800 RPM.  Have any of you had the issue of watching RPM while running your boat?  I have learned how to barefoot, so I'd like to keep a little higher speed/ smooth wake vs low end holeshot.

ACME's website recommends 449 - 515 - 525 - 653 - 1231 - 911 - 2083 in order from top speed to power torque.

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Woodski

@todens22:  The Sportster is a very light boat and small wetted hull area so not surprised it can run up to 5,000 rpm at WOT.  The 5.7 SBC (small block Chevy) can handle 5k RPM so not a worry, simply sounds as it is healthy.  You should be running pretty close to 100 RPM per 1 MPH at most speeds so 3,600 RPM @ 36 mph as an example with a 515.  If you are thinking of a prop change, I would consider a 449 as that will drop RPM by 150-200 RPM per MPH if you want to drop engine speed a bit.  Table and wake are very close between the 515 and 449, I have done that swap on my boat and really like the 449.  The 425 would be another option and is another 200 RPM step down in engine speed over the 449.

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UWSkier

Sporties are hot rods. Go up in pitch or have some cup added to your prop if you're concerned. I know indmar says 4800 in the manual but I believe the internals are the same as the Monsoon II which is rated higher. 

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formulaben
3 hours ago, UWSkier said:

Sporties are hot rods. Go up in pitch or have some cup added to your prop if you're concerned. I know indmar says 4800 in the manual but I believe the internals are the same as the Monsoon II which is rated higher. 

Most local prop shops can clean up your prop and add some cup for less than you think.

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