mercruiser gearing

Discussion in 'Sterndrives' started by ianmac09, Jun 30, 2010.

  1. ianmac09
    Joined: Jun 2010
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    Location: BC

    ianmac09 New Member

    I just killed my outdrive, upper gears destroyed:mad: . I have a replacement gear and bearing set available cheap but it is the 1.5 to 1 ratio. The engine is a 1991 4.3litre V6 and it has a high 5 prop. I think the stock gearing was 1.68 to 1 but not certain about that. So I was wondering how much the change in gearing will affect the performance, anyone?
  2. J3
    Joined: Jun 2010
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    Location: MI

    J3 Junior Member

    Since no one else has replied, I know replacement upper units come in 1.81 (for 1.84) 1.62 (for 1.65) and 1.47 (for 1.5). I think a lot of 4.3 v6s were mated with 1.84 gear ratio. I take it yours is a light boat?

    For the 1.65 to 1.5 keeping the same prop, if it was perfect before the new would lug the engine a bit. Would this affect how easy/quick it is to get up on plane? Top speed? Hard to say without knowing the particular boat. If it was perfect before, I'd sell and buy a new one on ebay and get what you know works well.
  3. ianmac09
    Joined: Jun 2010
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    Location: BC

    ianmac09 New Member

    Anyone want a 1.5/1 gear set

    Thanks for the reply, I discovered it is a 1.81/1 gear set (17-19) so changing to 1.5-1 is probably going to suck. For info it is a 1991 Campion Allante 175, so yes a fairly light boat. I bought the correct replacement parts online from Basic Power and so will get into fixing it next week, looks like a fun job.
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It will overload the engine. The piston will be really hot and may melt a hole. Also the valves may warp or burn.

  5. Jango
    Joined: Aug 2005
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    Jango Senior Enthusiast

    With the 1.5 gear your prop will be turning about 500 RPM more, 3000 vrs 2486 @ 4500 motor speed. Assuming your present prop is correct, you will need to drop 3 to 4 in. of pitch with less Dia or the motor will be overloaded.
    If you can work out the Prop the 1.5 ratio should be OK
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