conundrum ... repower engine choice for Uniflite 48 Convertible

Discussion in 'Diesel Engines' started by K_McIntosh, Mar 18, 2018.

  1. pacblue
    Joined: Apr 2018
    Posts: 22
    Likes: 1, Points: 3
    Location: Ann Arbor

    pacblue Junior Member

    Glad to hear you have found your boat.
    We had a 1978 42’ Uniflite SF with 6-71N’s for a number of years and know the 42’ hull well. It was about a 16 knot cruise with the 310hp Detroit’s if I recall. The Naturals were bulletproof and reliable, never had an issue with them.
    Enjoy your new toy!
  2. DPcaptain
    Joined: Oct 2020
    Posts: 1
    Likes: 0, Points: 1
    Location: Greece

    DPcaptain New Member

    I am starting a project on a 1980 Magnum 45’ with a pair of DDs’ 8V92Ti’s. The boat is located in Greece and has a cruising speed of about 23 knots (will check again soon). This boat will be doing daily cruises so the engines need to be reliable, clean, and economical to run/maintain. Currently the problem I see is that the boat is slow and the engines are thirsty, smokey and oily. The boats consumption if I remember correctly is about 250Lph (66Gph). Could you tell me what cruising rpm is most economical to run these engines at? Also where should they be topping out at? The current DD’s are in dear need of work that I will have to do regardless as I am not sure to manage to complete this research and project before the season starts (May 2021). I cant find any documents online on these engines, if you have anything it would be great. Also if you know where I can find replacement parts in Europe preferably.
    I am evaluating various options:
    Keep current engines if you believe they are up to the task but I am afraid they are too thirsty.
    Repower with new Man, Cat, MTU, Volvo...?
    Keep the propellers and shaft as is or change to surface drive? What speed and consumption would I gain?
    I would greatly appreciate your expertise and knowledge on this.

    Thanks in advanced,
  3. pacblue
    Joined: Apr 2018
    Posts: 22
    Likes: 1, Points: 3
    Location: Ann Arbor

    pacblue Junior Member

    The 8V-92TI’s should top out at 2350 rpm when properly loaded. Best cruise should be at 1950 rpm, anything more it cuts down on engine life.

    Your best choice is either the the MAN r6-800 or Volvo Penta D13 at 800 - 1000hp if you want the most top speed. Either one of these will cruise at a higher speed than the old Detroit’s.

  4. rangebowdrie
    Joined: Nov 2009
    Posts: 158
    Likes: 59, Points: 28, Legacy Rep: 10
    Location: Oregon

    rangebowdrie Senior Member

    I know that this is an older thread, and that this post does not pertain to the OP, that said;
    Having been the principal "caretaker" of a 1961 Chris Craft 55' motor yacht for ~12 years, I have nothing but praise for the original DD 8-71NA engines.
    They fire up before you can get your thumb off of the starter button. The owner says he usually runs them at anywhere from 1600>1800, and figures they will outlast the boat.
    AFAIK, their has never been any major work done on them, for seasonal pleasure boat use they are great engines.
    Given the choice, for higher speed/power, I think I would prefer a 12-71 over an 8-92,, the exhaust note is more pleasing:).
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