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Detroit 4-71

Discussion in 'Engines' started by Oceanus Est, Jan 31, 2017.

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  1. Oceanus Est, Jan 31, 2017
    #1
    Oceanus Est

    Oceanus Est New Member

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    I find little mention of Detroit 4-71 in this section. Are these that rarely used in civilian marine applications? In particular, I'm researching a claim of making 300 HP with one of these 2 stroke, 284 cuin motors. Seems very high! Can anyone share applicable experience?
  2. SeaEric, Jan 31, 2017
    #2
    SeaEric

    SeaEric YF Historian

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    It takes turbo and intercooler to get the 4-71 to 300 HP. AKA "4-71ti"
  3. Capt J, Jan 31, 2017
    #3
    Capt J

    Capt J Senior Member

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    In all honesty, theres nothing wrong with the 4-71, you just don't and never have come across many in the real world....6-71's you see TONS of, 4-71's not so much.
  4. RT46, Feb 1, 2017
    #4
    RT46

    RT46 Senior Member

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    I agree, they are kind of rare in marine environment.
    4-71s are common in some older land generators and heavy equipment.
    An extremely reliable and bullet proof engine.
    I bit loud, but makes a distinctive sound.
  5. Lepke, Feb 1, 2017
    #5
    Lepke

    Lepke Member

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    Actually many 471s were built in WWII to run generators in ships. Many steamships had one driving an emergency generator. Minesweepers like the Calypso had 2. Gray Marine made 1, 2, 3, 4 cylinders in 71 models. The 171 has a compression release and was hand started. A 271 will run a 20kw generator. There were many 3 and 471s in smaller commercial boats.
    A 671ti can make 450+hp so a 471ti should be able to do 300hp. For about 2500 hours. Maybe less.
    You can't just add a turbo and intercooler to a natural 471. The compression ratio, fuel and water pumps are different. The ti has a 4 valve head, too. If you need 300 hp, you'd be better off with an 8v71 natural. While the engines will produce max hp, running like that creates excessive exhaust gas temperatures that wear away the cylinder components. Turbo engines run at near full power only get half as many hours between overhaul, maybe less. Turbo engines burn much more fuel, too.
    Just because the coolant isn't overheating doesn't mean the EGTs aren't too hot.
  6. PacBlue, Feb 2, 2017
    #6
    PacBlue

    PacBlue Senior Member

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    Noisy like you wouldn't believe.
    A new (back then, circa 1980's) 48 Chris-Craft Double Cabin Cockpit Motoryacht (based on the old 42' Uniflite Double Cabin design) had them fresh from the factory, you could hear that boat before you ever saw it, will never forget the unbearable loud exhaust note as we passed alongside her in the harbor! Almost as bad as a 38' Blackfin with 6V-92TA's and straight exhaust pipes, no mufflers.
  7. Capt J, Feb 2, 2017
    #7
    Capt J

    Capt J Senior Member

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    That reminds me, I ran a 1979 41' Viking SF once with 6-71 Naturals, this boat was unbearably noisy on the flybridge and in the cockpit at 9 knots and below. You had to literally yell to someone sitting next to you. Horrible.....noisiest boat I ever ran.
  8. Oceanus Est, Feb 2, 2017
    #8
    Oceanus Est

    Oceanus Est New Member

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    I've heard the noise comment before. The boat I was considering had a control station _only_ on the FB. I think we know why.
  9. Oceanus Est, Feb 3, 2017
    #9
    Oceanus Est

    Oceanus Est New Member

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    Eric, my original question wasn't clear. I understood that the 4-71TI is spec'd at 300HP. I meant that it seems high with respect to reliability/life for that size engine. Lepke (thanks) has shared the conventional wisdom on huffed up DDs including 2500 hours between O/H. I think there are not enough 4-71TIs out on the pleasure marine market to expect to hear a first hand account.

    Considering I want to run at displacement speeds with just enough extra "authority" to manage coastal currents, I should look for a differently powered boat.
    Last edited: Feb 3, 2017
  10. baltimore bob, Feb 3, 2017
    #10
    baltimore bob

    baltimore bob Member

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    300 is stretching the rubber band real tight for a 4 71. You can get decent time between overhauls simply by not running them on the pins. The noise can be addressed, I worked on a couple classic charter yachts with 6 71s and managed to muffle the exhausts to a level where some people found it hard to believe.
  11. Capt Ralph, Feb 3, 2017
    #11
    Capt Ralph

    Capt Ralph Senior Member

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    I found a Carri Craft cat house boat years ago with 4-71Ns in her. My father almost bought her.
    I thought it was a cool set up.
  12. Capt J, Feb 3, 2017
    #12
    Capt J

    Capt J Senior Member

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    They'd be fine to run at 1000 rpms for 6 hours, then run them at cruise for 30 minutes to blow them out..... no reason they shouldn't have the same life cycle as a 6-71 TI, I would expect 3500 hours out of them.....5000 if you run them easy.....a 4-71 can't be that costly to rebuild either. DD TI's are a lot quieter than Naturals.......at least half as much noise.
  13. captholli, Feb 3, 2017
    #13
    captholli

    captholli Senior Member

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    If I remember correctly the late '70s Hatteras LRC 58 & 65 had 471 naturals standard and Hatteras offered the 671 as part of their upgrade package. I would look at a LRC cruisers blog or forum for info.