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Thread: Detroit Diesels

  1. #1

    Detroit Diesels

    Have been researching some older Hatteras (1979 - 1990). I know the DD 6-71's are great motors. Can anyone give me insight on 6V 92 TA, 8V 71 TI, 8V 92. If maintained properly which ones should I be looking at? Thanks!

  2. #2

    Re: Detroit Diesels

    IMO, Always lean to the 71s.
    The 71s dry cylinder liners are more forgiving.
    The 92s offer a lil more horse power for near the same sized package but have wet cylinder liners. These liners are not as forgiving as the 71s. The 92s liner O rings keep coolant in its place but can be a problem issue. When they do fail, it requires a near complete engine tear down to repair.

    Lots of common bolt on parts are interchangeable between all the 71s since the 1940s, Some hang on parts are interchangeable from the 71s to the 92s.
    Both use the same oil, coolant, most filters.

    IMO, the 71s run a lil cleaner at extended low speed operation.

    If you want to go fast more than slow, the 92s may offer a lil more performance for those that can afford to pour the fuel in.
    But like a car, performance is not cheap and shorter lived engines.

    At no extra charge, the model numbers can be confusing so here is a primer to help you understand the model numbers;

    The series number (52, 71, 92, 149) references the cubic inch per cylinder.
    So say a 271 engine is 142 CI engine.
    If a V is not in the model number, it is an in line engine. With the V, it is a V block like the V8 in some cars.

    All 2 stroke Detroits must have a blower (super charger) to run. Not for performance but to blow air thru the engine and clear the cylinders. These engines are called Naturals (N).
    T for turbo charged. Compressed air into the engine at higher RPM raises the compression ratio and makes more HP. (T).
    For turbo inter cooled. The turbos fresh compressed air is cooled between the turbo charger and the super charger. Cool air helps the engine make a few more ponies (TI).
    TA for turbo after cooling. This cools the fresh compressed air after the super charger. Ensures that air is pretty cool rite before it is blown into the cylinders.
    Blower bypass; Sometimes the turbos deliver so much air flow, the gear driven supper chargers slow the air down. If we free spin the blower rotors, more turbo air pressure to the lungs (B).

    Many TAs seem to automatically have bypass blowers.
    Some real race horses come with TI and TA.

    Examples;
    671 or 671N, Natural in line 6 cylinder, 71 series.
    671 TIB, in line 6 cylinder turbo charges, inter cooled air, Bypass blower.
    6V92 TIA, V 6, 92 series, inter cooled AND after cooled. Bypass is assumed with the TA option.

    But wait, There's more.
    The same model number can be tuned with different horse power levels. By changing the turbos and fuel injectors, So a 12V71TI can be tuned from 650 HP to near 800 HP.

    Using an old Caterpillar guide, instead of engine hours, imagine the amount of fuel the engines consumes between overhauls.
    With your foot in it making lots of horse power, you consume more fuel (VS a clock) than going slower and not making horse power.
    The less HP you ask of the engine, the less fuel it consumes, the longer it will last VS a hour timer.
    So a 160HP 671(N) could last up to 8000 hours, a 485HP 671TIB making lots of HP may need a rebuild in 3 - 4000 hours.
    You will never get all the records when purchasing a boat, just lip. This is why a thorough engine survey by an ole grey haired and real Detroit tech in so important. They can examine a few places and tell you if there is any life left in the engines.

    Keep us up at what your looking for.
    As You can see thru this forum, some folks know the boat listed and can offer extra thoughts.
    Last edited by Captain Ralph; 07-31-2022 at 04:07 PM.

  3. #3

    Re: Detroit Diesels

    I have to ad;
    Many members here have 92 series engines.
    They are well maintained and their owners love them.
    That extra effort to properly take care of their 92s has paid off for them.
    So, I did not mean to bad mouth the 92s, I just like the 71s better.

  4. #4

    Re: Detroit Diesels

    I will add a recommendation regardless of 71 or 92 is to closely evaluate/service turbo's, intercoolers (or after), exhaust manifolds, injectors, heat exchangers, and water pump housing. Even if engine passes survey with flying colors make sure all these items are in perfect condition. Otherwise issues will arise. I know the hard way.

    Establish a new baseline including oil samples on whatever you buy. DD 2 strokes get a bad rap from lack of maintenance. The only "true" myth is that yes, the due burn a bit more fuel but nothing crazy. Other than that take care as required per your configuration. Love them. Only way to stop them is to cut off fuel or air. They run better hurt than some do healthy. Means a lot when the sky turns black.
    1966 34c
    1982 46 HP

  5. #5

    Re: Detroit Diesels

    I sure would like information on how to service exhaust manifolds, injectors, heat exchangers, and water pump housing. I don't have turbos or after coolers, etc. on my 471N's, but haven't gotten into the servicing of these parts yet.

    Is this in a online guide by chance?

  6. #6

    Re: Detroit Diesels

    Quote Originally Posted by zigzag930 View Post
    I sure would like information on how to service exhaust manifolds, injectors, heat exchangers, and water pump housing. I don't have turbos or after coolers, etc. on my 471N's, but haven't gotten into the servicing of these parts yet.

    Is this in a online guide by chance?
    Manuals on e-bay.
    Hard copy or CD

  7. #7

    Re: Detroit Diesels

    Thanks for a very succinct summary of the DD lineup.
    Jim Grove, Fanfare 1966 50MY Hull #22 (Delivered Jan. 7, 1966)

    "LIFE IS JUST ONE DAMNED THING AFTER ANOTHER." Frank Ward O'Malley, Journalist, Playwright 1875-1932

  8. #8

    Re: Detroit Diesels

    I do have the owners manual and service manuals. They do cover a variety of installations, including industrial, generator, etc - so no specific to marine.

    Looking at the 471N's on my 58LRC I don't believe I have air cleaners or water cooled manifolds. I do have a "silencer" on the blower. Does this have a replaceable element int it? I didn't think so.

    As far as exhaust manifold maintenance again - I don't see that these are water cooled. Is there some sort of maintenance on them?

    Don't see the answer to either of these Q's in the owners manuals

    Thanks

  9. #9

    Re: Detroit Diesels

    I have the same boat. My 471Ns have water cooled exhaust manifolds. I'd be surprised if yours were different. Look under the manifolds. You should see a coolant drain cock..

  10. #10

    Re: Detroit Diesels

    Very good info!

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