Repower ideas for my 28' Uniflite Sport Sedan?

Discussion in 'Powerboats' started by Persistant, Mar 26, 2015.

  1. Persistant
    Joined: Mar 2015
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    Location: Vancouver Island

    Persistant New Member

    After sitting for a couple years my 340 crusader(single) is going to need to rebuild. With the present power it doesn't plane and cruises at 10 to 12 kn if I'm considering repowering the boat I'm looking for ideas of what motor would be big enough to get the boat up on the step and economically cruise. I have been searching the net looking for other guys with the same boat who upgraded to a bigger powerplant with the single screw shaft drive to see what experience they have had. The other option I was considering was maybe putting a stern drive package in the hold although I have to look at transom strength and depth height difference between where the original engine sits under higher back and the rear deck being lower. My friend who is a marine mechanic and I have been discussing the different options also including going to the diesel but the length of the diesel would require me to go to a v drive likely because of the difference in length of the engine but that's still not out of question. At the end of it all I really want to make sure that I can do it as economically as possible to make the most sense I may just end up having to go to the same setup and give me the same performance but I really would prefer to have the boat plane if it wasn't too much more. I seem to recall the weight with fuel and water was about 11,000 lbs. I found the posted factory weight saying 8600 lbs?
    Does anybody know of anyone who presently have the same boat with a single screw with bigger power that makes the boat plane?
     
  2. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    IIRC small block mopars weigh a touch over 500 pounds.

    A Cummins 5.9 is over 1100 pounds,so 600 pounds more plus a stronger trans. maybe 650 more pounds.
    Plus the costs of a used 5.9, plus exhaust, cooling, beds, trans work is going to be much much more than a simple gas engine upgrade.

    How about a Chev LS out of a junk yard truck?
     
  3. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Crusaider by far makes the best replacement engines

    Rebuild or just get a new one , there have been many improvements over the decades.

    Empty your boat of EVERY item on board , you may find a ton of "stuff" that is nice , but not need to have,
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    How long have you had the boat? If the engine was worn when you bought it, then the engine never produced in rated power. However, for more power a modern GM 5.7 is producing 325HP, basically the same as an older big block. Your older engine is probably rated at 230HP or so.
     
  5. Persistant
    Joined: Mar 2015
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    Location: Vancouver Island

    Persistant New Member

    I've had the boat for about 7 years and was told when I bought it that the motor had 170 hrs on a fresh rebuild. Everything looked new such as manifolds, mufflers etc and was quiet tidy. I ran the boat on and off for 3 years and then made a career change which didn't allow for much fun time. One winter the heat exchanger froze, and then more sitting, carb deteriorated, I then decided to get a new one. Now I have more time and decided to get it back into the water and found that upon rotating the motor by hand it came up hard on a stuck valve. Short version…pulled motor, drained 2 gallons of water from oil pan, pulled heads, scored and pitted cylinders, 0.30 pistons already…..time to re power or rebuilt present motor. I have been told it is not a good idea to go over 0.30 in a marine engine, I would like to have the boat plane to be more versatile as I want to be able to go for a 4 hour fishing trip rather than spending the day every time. My marine mechanic buddy suggested the GM 8.1 but also suggested seeing if I could find someone that had already done this with success by either setting it up with the existing shaft drive or modifying the setup for a stern drive.
     
  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The 8.1 had not had much success on marine uses. VolvoPenta was the first to marinize them, and I troubleshot the first that failed. The upper ring would rip the top edge of the piston off. They specified new pistons, and it helped but they were still failing with hard use. The pistons are really short to minimize friction and weight. In cars/pickups they never get run at 5000 RPM for hours. I like the power/weight ratio of the engine, but durability is not the best.
     
  7. Persistant
    Joined: Mar 2015
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    Location: Vancouver Island

    Persistant New Member

    That's too bad. I had heard they had great torque for that kind of application.
     

  8. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 109, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Before installing more HP than stock it would be wise to look at the installed shaft and prop to see if it can handle the bigger HP and weather a larger diameter shaft and prop will be required.

    Cheaper to scrap the boat and find a running boat that goes the speed you noe want.
     
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