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Detroit 3-71 max kw?

Discussion in 'Generators/Gensets' started by Bergz22, Sep 16, 2020.

  1. Bergz22

    Bergz22 Well-Known Member

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    What is the largest kw rating a Detroit 3-71 NA will run?
     
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  2. Delmer

    Delmer Senior Member

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    Are you planning to buy a generator end to attach to your engine? or looking for general info? Are you looking for standby, or prime rating?

    That would be a poor choice for a generator engine these days, but I'd guess you'd get 50KW out of one, don't know if anyone would have built that package though, the engines being so cheap and the generators being expensive, I'd think they'd mostly be derated more like 30-40KW (a 371 won't make 3600 RPM, and won't make peak hp at 1,800RPM)
     
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  3. Bergz22

    Bergz22 Well-Known Member

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    I’m looking to convert a 1800 rpm to a 1200 rpm. The crew complains about the noise. It will be continuous duty.
     
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  4. John C.

    John C. Senior Member

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    I take it you are going to install the engine on a 6 pole generator then?

    I can find the engine rated at 113 horsepower at 2,100 RPM. Drop the turns to 1,200 and you will likely only have half the HP and next to nothing on torque.
     
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  5. Delmer

    Delmer Senior Member

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    replace the engine not the generator end.
     
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  6. old-iron-habit

    old-iron-habit Senior Member

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    You will not even get half the HP at 1200 RPM and very little torque. The 3-71 makes nearly all its power from 1550 to 1800 RPM.
     
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  7. Bergz22

    Bergz22 Well-Known Member

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    I would like to replace both, but the company doesn’t want to spend the money.
     
  8. Vetech63

    Vetech63 Senior Member

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    You better replace the engine then. Running that engine at 1200 RPM wont have enough torque curve to run a generator.
     
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  9. spark

    spark Member

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    3-71 1200 RPM 30kw 1800 RPM 50kw These sets were used on towboats for many years. Finding a 1200 rpm generator very difficult Most were Delco but not made anymore.
     
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  10. crane operator

    crane operator Senior Member

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    If you have room in the cabinet, a 4bt cummins would have better torque at the rpm's that you are wanting to run. Will the generator perform correctly with the lower rpm's?

    I agree with everyone else, the low rpms will not be suitable to a 3-71. They need the rpms.
     
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  11. Birken Vogt

    Birken Vogt Charter Member

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    As spark noted they were run at 1200 RPM for generators all the time in the olden days. But you need to find a 6 pole 30 kw generator end to do it. I suspect the governor and many of the engine parts such as camshaft were different for a 1200 RPM spec engine instead of 1800 RPM as well. The last 1200 RPM Detroit I saw was rotting in some guy's yard under a ratty tarp, and he passed away and I suspect it has become Chinese razor blades by now.
     
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  12. Bergz22

    Bergz22 Well-Known Member

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    Some other towboats I worked on had 1200 rpm Detroit’s. But were 30 kw.

    Thanks for all the info. I’ll just leave it as is. Just trying to figure out a solution for the crew. I wish I was able to spend the money on a new gen set.
     
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  13. Welder Dave

    Welder Dave Senior Member

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    Ear plugs are cheap.
     
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  14. Bergz22

    Bergz22 Well-Known Member

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    I agree. But telling 7 guys to wear ear plugs when they sleep doesn’t always go over so well.
     
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  15. mitch504

    mitch504 Senior Member

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    I have a friend who is in the boat salvage business, he is 88 yrs old and has some good running generators just like what he learned on, some 5 yrs old, and everything in between!

    I'll ask if he has any 1200 rpm stuff.
     
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  16. Bergz22

    Bergz22 Well-Known Member

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    That would be great. I would also be interested in a 4bt generator engine and cat 65-75 kw ends.
     
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  17. MarshallPowerGen

    MarshallPowerGen Well-Known Member

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    Is the set in an enclosure or open? There's really only so much you can do sound-wise with a Detroit.

    4bt is a good option, so is the Iveco 445, Deere 4045, etc. 50kw is what's primarily used on cell towers, and that means there's a lot of options out there (Mitsubishi, Hino, Perkins).
     
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  18. Bergz22

    Bergz22 Well-Known Member

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    It’s open, in the engine room right below the bunk rooms. The other gen is a 4045. They run it to death.

    Problem is for the foreseeable future there is no new equipment allowed.
     
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