1982 Astroglass Runabout

Discussion in 'Gas Engines' started by ChevyLover, Sep 16, 2017.

  1. ChevyLover
    Joined: Sep 2017
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    Location: fort knox,ky

    ChevyLover Junior Member

    I have a broken 3.8 I want to install a small block will the lower unit handle the v8? and why is everyone telling me my boat will sink if I put a v8 in it?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Which drive do you have? If it's an Alpha, then the gears will be wrong for the V8 and the lower unit gear set isn't up to much HP.
     
  3. DSR
    Joined: Mar 2017
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    Location: Michigan

    DSR Junior Member

    Hi ChevyLover,

    If I remember, there's less than 75 lbs difference between the Chevy 229 and a small block, and with most of the accessories being interchangeable, there shouldn't be any problems with dropping a small block in the hull. You will have to sort out the outdrive though. Not a huge issue if it's an Alpha. If it's an OMC, I understand that finding drives and parts can be a major PITA......

    Thanks
    Dave
     
  4. ChevyLover
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    Location: fort knox,ky

    ChevyLover Junior Member

    thank you it is a older omc believed to be like a 800 I have the serial number if it will help
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's not the weight that's an issue with the 90 degree V6 that's the issue, but the RPM band it uses as well as the torque it develops compaired to the small block. The gear set and shafts for the L4's and V6's are smaller, weaker and use higher RPM targets. A very modest small block can be used, though will spin too quick at WOT. Much more then 200 HP and you'll quickly find the weaknesses in the lower case.
     
  6. ChevyLover
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    Location: fort knox,ky

    ChevyLover Junior Member

    is a 3.8 car engine and a 3.8 boat engine the same or is the a difference in the cams or cranks
     
  7. DSR
    Joined: Mar 2017
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    Location: Michigan

    DSR Junior Member

    The major components of the engine are the same (block, crank, heads, etc). The cam could possibly be marine-specific but I'd doubt it.

    Sorry PAR, I was addressing ChevyLover last question first, referring to the boat sinking if he put a V8 into it (presumably concerning a weight difference) using a small block Chevy as a prime example (the easiest to swap over with the engine architecture being essentially the same). I did also agree with what you said stating that, yes, there are differences in the outdrives with it being equipped with a V6, and those differences would need to be addressed.
    I apologise if it didn't read that way....... :)

    Thanks
    Dave
     
  8. ChevyLover
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    ChevyLover Junior Member

    thank you all so much for the info it has helped a great deal
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    No worries Dave, I think I read it right. The marine cam is different, setup more like a stationary engine profile, than an automotive application. The other internals are automotive on all the low output GM engines, including the MK4. Swap out an LS and the weight difference will be on the positive side!

    My only concern, like yours was the drive gear set and shaft sizes.
     
  10. ChevyLover
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    Location: fort knox,ky

    ChevyLover Junior Member


    thanks that's my main concern also
     
  11. ChevyLover
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    Location: fort knox,ky

    ChevyLover Junior Member

    so the best thing to do is get a 4.3 for the bigger pistons and use the 3.8 cam? will this be a good decision?
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The 3.8 cam will fit, but it's not going to work as well as the 4.3 cam. The 4.3 came with a different crank and bigger valves, so the cam profile took advantage of these features, which made a true "even fire" engine. Additionally the year can screw with you, as they installed a balance shaft, because even though it was a even fire, it wasn't all that smooth. The tell is the lack of a mechanical fuel pump provision. The boss is still there, just no hole for the push rod or bolts. If getting a 4.3, get a pre 1991.
     
  13. DSR
    Joined: Mar 2017
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    Location: Michigan

    DSR Junior Member

    Hi,

    Doing a 4.3 in place of the 3.8 should be a very good alternative. I would get a new marine cam specifically for the 4.3.
    The 4.3s came with both hydraulic flat tappet and hydraulic roller cams so you would need to figure out which one you need for the engine you get your hands on. If you get a clean roller engine you can reuse the lifters as they don't create a wear pattern with the cam that the flat tappets do so you just need a cam for those engines. Otherwise buy a cam and lifter set if it's a flat tappet engine.

    Thanks
    Dave
     

  14. ChevyLover
    Joined: Sep 2017
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    Location: fort knox,ky

    ChevyLover Junior Member

    thank you guys so much
     
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