volvo penta 270 ratios

Discussion in 'Sterndrives' started by mbwrx, Sep 5, 2008.

  1. mbwrx
    Joined: Sep 2008
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    mbwrx New Member

    hello ,this is my first post,i had a search for this info but cant seem to find it ,please forgive me if its on here somewhere,i have a 19 ish foot sealine power boat.that i bought in bits.originaly fitted with volvo penta 5.7 v8 petrol,and 270 volvo penta stearn drive.i am fitting a 6.2 gmc diesel.i would imagine this has been done a few times before,anyway my question is will i have to change the gear ratio of the leg .to allow for the rpm difference.the gmc has 150hp @3600,i would guess the petrol engine would have revved a good bit higher,any input would be apprecated .cheers .martin
  2. tuantom
    Joined: Jan 2005
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    Location: Chicago

    tuantom Senior Member

    The gear ratio for that drive is 1.61:1. Not sure what the diesel gear ratios were; but I would guess a bit lower being that the v8 probably spun around 4400 rpms. Seems close enough that a propeller change could compensate though.
  3. Çemberci
    Joined: Apr 2007
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    Çemberci Senior Member

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  4. 2850 Bounty
    Joined: Oct 2008
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    Location: Portland, Oregon

    2850 Bounty Junior Member

    Martin, in this series drive, I believe that you are limited to the 1.61:1 over-all gear ratio.
    This is the tallest ratio in the SP drives of that vintage that I am aware of.
    The diesel needs the taller ratio.... not lower!

    The OHC 4 cylinder is 2.15:1....
    The inline 6 is 1.89:1....
    The V-8's are 1.61:1

    You may be able to make it work..... however, swapping props to compensate for an incorrect gear ratio NEVER actually works.

    You'd have to go with a Duo Prop lower unit to get into the correct range for a lower RPM diesel engine.... the 1.78:1, for example. There is also a 2.30:1.

    Rick E.
    2850 Bounty on the vBulletin BOC forum.
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