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  1. #1

    Cool Omc '84 i/o 2.5 l 252sthrcra rpm

    Hey, I'm looking to find what the RPM should be when the engine is wide open on an '84 OMC I/O 2.5L engine (model 252STHRCRA.) We bought the boat used and it didn't come with the owners manual. Right now we're specifically wondering about the RPM to replace a prop, (we don't know if the prop on it is the ideal, but we heard you can find out the ideal by using some equation with the boat's current RPM and the ideal RPM when it's wide open.) If anyone is an expert on this engine and has any other helpful advice, we'd love to hear anything you have to give us! This is our first boat, so we are soaking up all the info we can. Thanks!

  2. #2

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    Quote Originally Posted by fishergirrl View Post
    Hey, I'm looking to find what the RPM should be when the engine is wide open on an '84 OMC I/O 2.5L engine (model 252STHRCRA.) We bought the boat used and it didn't come with the owners manual. Right now we're specifically wondering about the RPM to replace a prop, (we don't know if the prop on it is the ideal, but we heard you can find out the ideal by using some equation with the boat's current RPM and the ideal RPM when it's wide open.) If anyone is an expert on this engine and has any other helpful advice, we'd love to hear anything you have to give us! This is our first boat, so we are soaking up all the info we can. Thanks!
    around 4000 rpm with a 13.75 x 19 prop

  3. #3
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,538

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    I'm looking to find what the RPM should be when the engine is wide open on an '84 OMC I/O 2.5L engine
    Ayuh,.... 4400- 4800 rpms, at Wot,......
    Any Grease is Better,... Than No grease at All....

  4. #4
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,538

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    Quote Originally Posted by capn nate View Post
    around 4000 rpm with a 13.75 x 19 prop
    Ayuh,..... Yer luggin' yer motor,...... drop down to a 17" pitch,....
    Any Grease is Better,... Than No grease at All....

  5. #5

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    Quote Originally Posted by bondo View Post
    Ayuh,..... Yer luggin' yer motor,...... drop down to a 17" pitch,....

    i get 30-32 mph on a 19p at 4000 -4200rpm with 4 souls on board....18.5' renken bowrider 995
    2.5l omc 400 stringer its an 83 original dont really want max rpm 17p prop would raise rpms beyond 4000- 4200

  6. #6

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    ideal rpm imo is 4000 -4200 i can go higher rpm but it wont achieve anything and it cant be good running max rpms on motor

  7. #7
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    10,029

    Default Re: Omc '84 i/o 2.5 l 252sthrcra rpm

    FYI.... and for what it's worth....... the OEM WOT RPM rating for a given Marine Engine is a Test RPM ONLY...... it is not an RPM that is to be sustained for any duration (unless of course, you wish to drastically shorten the life of your engine).

    The test is used to determine if your drive reduction and propeller size/pitch are correct for the engine and hull.




    .
    Last edited by RicardoMarine; 04-04-2018 at 10:19 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

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