HELP PLEASE! 5.7l omc max speed 30mph @ 4k rpm

V

vegasnoid

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Apr 28, 2012
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Here's my problem; I bought a '88 Four Winns 205 Sundowner, with a 5.7L OMC Cobra engine. Engine was seized, so I had it Completely rebuilt, everything new. I took it out for the 1st time today with a 15"-17 prop and it would only go 30 MPH & the RPM's wouldn't go above 4k. I changed prop to a 14 1/2"-19 and it hit 40 MPH but still the RPM's wouldn't go above 4k. Am I running the right prop? I was hoping for a faster top speed and to get my WOT RPMs up to the proper range. Any suggestions?
 
BonairII

BonairII

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Jun 7, 2011
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Re: HELP PLEASE! 5.7l omc max speed 30mph @ 4k rpm

I may be wrong, but I don't think you shouldn't be running it hard just after a rebuild.
 
sam60

sam60

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May 21, 2011
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Re: HELP PLEASE! 5.7l omc max speed 30mph @ 4k rpm

Hello Neighbor....check out the prop page on this site. How are you breaking in the rebuild? If re-builder didn't offer info, you should look into it.
 
sam60

sam60

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May 21, 2011
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Re: HELP PLEASE! 5.7l omc max speed 30mph @ 4k rpm

BonairII said:
I may be wrong, but I don't think you shouldn't be running it hard just after a rebuild.
Click to expand...

I read about a detailed break-in with rpm variances for certain time periods and did the best I could with it first time out with rebuild. First 10 hours are important.
 
a70eliminator

a70eliminator

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Re: HELP PLEASE! 5.7l omc max speed 30mph @ 4k rpm

Speed increased as one would expect with bigger pitch, rpm max stayed the same, this tells us the engine has adequate power and is rpm limited by either not enough fuel ( small jets) throttle not opening completely, or something ignition related. Hopefully your not wringing it out watching a bad tach, you may want to hook up a shop tach to verify it cause 40mph isn't too shabby for that size of boat.
 
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