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Clarification on the DD 6-71 n, 6-71 ti, and others

Discussion in 'Engines' started by ShearPleasure, May 1, 2022.

  1. Looking at DC MY 42-53 ft. I know the 6-71s are good reliable engines along with the 3208 cats but I am finding a few different 6-71s. Does anyone have a quick explanation on what is the best, more reliable 6-71s. Even saw a 8v 71 ti. What are your thoughts on this engine? Thanks!
  2. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    11,023
    Location:
    Satsuma, FL
    The straight 6-71 offers the strongest crank shaft. A block bearing between each rod throw. These bearings are rather massive.
    Still, life span does shorten notably after 450Hp.
    DDC did release a 485HP version. Others pulled over 500HP out of them. Life spans are shorter past 75hp per lung IMO.
    The V blocks are shorter (for/aft), but with more lungs. 2 rods between every block bearing.
    You could be amazed, the most reliable HP from a 8V71 is still 450HP.
    It is just in a shorter and maybe lower package.
    More displacement-- more torque-- better reduction,, I feel the 450HP, 8V71TI could have been DDCs most solid engine.
    In the V blocks, After 60HP per lung shortens it's life span IMO.
    Typical factory TI engine life could exceed 4000 hours.
    Well maintained naturals can last your life time.

    From 6V71 to 12V71, reliable HP up to 750 is available.
    12V71TAB could turn more that 900HP+ but now your MTTR is 2000 hours.

    Keep your foot out of it and fast idle around with most of us, and your engine life (and MPG) increases quickly. At fast idles, your still moving and only making 100 to 150HP.
    It just when you make HP your causing greater wear on your engine. It's just not the gas pump bell ringing away.

    Years ago, not mentioned lately, Cat use fuel consumed to measure the time between overhauls. I like this measure better but for the recreational user, hours seems to be easier.

    When the designers got bored, they just started bolting blocks together end to end for even more power (24V71TAB)
    Combining separate engines together in-line or star patterned into a common clutch/gearbox was also done.

    If you are new to Detroits, Remember, these are 1938 designs. Most parts from then to now are still interchangeable.
    For what they were back then, They were considered light weight engines.

    The Horse Power of the engine is generated from different tunes starting from the natural engine (required blower only) to engines including many different turbo chargers, air coolers, cam shaft timing adjustments and injector sizes.

    MTU now owns the Detroit Diesel lines and keep committing to support these ole dinosaurs. There are just sooo many of these still out there, it would be like shooting your self in the foot to stop supporting them. But sadly, the cost of new parts keep going up.

    I still prefer any Detroit 71 series over any 3208.

    You may find 53 and 92 series DDC engines. I do try to steer people away from these if a 71 series boat is also available.
    With wet liners, they are a lil more complicated and expensive to maintain. I also feel not as forgiving as the 71.

    Hope this was helpful,
    rc
    JWY likes this.
  3. Thanks Capt Ralph. Very good information, and good stuff!
  4. YachtForums

    YachtForums Administrator

    Joined:
    Dec 22, 2002
    Messages:
    20,057
    Location:
    South Florida
    Great post Ralph.

    This thread has been moved to the engine forum for better indexing.