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Fuel economy detroit diesel 8v92

Discussion in 'Engines' started by aircar, Aug 10, 2011.

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  1. aircar, Aug 10, 2011
    #1
    aircar

    aircar New Member

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    Location:
    Lewisville, Texas
    Am considering buying a Hatteras 58 with DD 8v92T's. If I want to operate the boat at hull speed, what can be done to increase fuel economy?
  2. Capt J, Aug 11, 2011
    #2
    Capt J

    Capt J Senior Member

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    Hull speed is very fuel efficient to start with, however you can put smaller injectors, but you'll have to take pitch out of your props, lose cruise speed, and have to have the rack adjusted.

    At 1000 rpms you'll burn 10-12gph (both engines)
    At 800 rpms You'll burn around 7-8GPH (both engines)
    At cruise 1900-1950rpms......around 60gph.....
  3. Capt Ralph, Aug 11, 2011
    #3
    Capt Ralph

    Capt Ralph Senior Member

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    Save your 92s

    There is lot of reading out there you need to do before changing injectors and props. To help you along on this, May I save you some time; DO NOT change the injectors or props.
    Slowing down will save fuel. However keep in mind, The 92's are big, hold a lot of coolant, move allot of sea water thru them. They were built and designed for H P. At a fast idle, they will not come up to proper temperature and fuel burns in the cylinders may not be complete.

    We run our 12v71TIs at fast idles around 10 knots. Every couple of hours, I'll lean on one (14-1500 rpm) for about 10 minutes. It stinks for a few seconds but the temp comes up, exhaust clears and I know the rings, pistons and cylinders are clear of unburned fuel and slobber, Then I idle that one back down and lean on the other for a few minutes. Doing one at a time puts a nice load on them and temp comes up in just a few minutes. Boat may speed up a knot or two and the pilot keeps the course straight.

    We can not afford to pour diesel into our motors but during our two week vacations we cover some latitude. We have to run for 10, 15 and once 20 hours this way on legs from Jacksonville FL to the Bahamas and back. Engine oil stays clean.

    One night we timed the current / wind wrong at Ponce Inlet (south of Daytona FL). It was real nice to have all 1300 H P on line when we needed it.

    Slow down. Care for your engines. DON'T de-tune.


    An old phrase I remember;
    L S D; Low Speed Displacement.
  4. Capt J, Aug 11, 2011
    #4
    Capt J

    Capt J Senior Member

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    I did the entire Great Loop with a set of 12v71' TI's in a 75' Hatteras MY. We ran at 1000 rpm's and then I ran the engines at a high cruise speed 2000 rpms (slowly brought them up 1400 for a few mins, 1800 for a few mins, then 2000) for around 30 mins to clear them out. Everything was fine. The engines would maintain 170 degrees or better at 1000 rpm, not so much at 800 rpms.......Some days we ran slower than 1000 rpms and more like 700-800 due to our wake and such on the rivers heading south. We averaged slightly less than 1.5 GPM including generator over the entire trip. I did run at cruise a couple of those days as well.
  5. Capt Ralph, Aug 11, 2011
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    92s are cool, 71s Rule.
  6. Paul S, Feb 13, 2016
    #6
    Paul S

    Paul S New Member

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    Looking for a new Detroit Diesel 8V92T
    Can someone suggest a good place to look for one at a great price ?
  7. RT46, Feb 13, 2016
    #7
    RT46

    RT46 Senior Member

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    I didn't think you could use the words "fuel Economy and Detroit Diesel" in the same sentence
  8. Capt Ralph, Feb 13, 2016
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    Sad to say; there are no more NEW 92s. Where are you at? What are you really looking for?
    There are shops that rebuild. There are shops that sell rebuildable cores and/or running take outs.
    Your looking for what, really?
  9. Bamboo, Feb 13, 2016
    #9
    Bamboo

    Bamboo Senior Member

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    Those who have repowered from a DD to a CAT in 65 Donzi's with similar HP have the same cruise speed and fuel burn at top end and cruise- but the DD burn less at hull speed.
  10. Capt J, Feb 14, 2016
    #10
    Capt J

    Capt J Senior Member

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    I've usually seen boats repowered pick up 3-4 knots by going to new 4 cycle engines versus the old D.D. 2 cycle engines at cruise and top speed with the same HP rating. A 6 cylinder C18 acert, puts out the same HP as most 12 cylinder 92s. The weight savings are usually 3-4000 lbs lost on 12 cylinders. At 1000 rpms or under, the D.D. 2 strokes do use about half as much fuel as a 4 stroke with the same HP rating.
  11. Lepke, Feb 20, 2016
    #11
    Lepke

    Lepke Member

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    There's a guy in Tacoma that buys engines for resale or parts. He's always on ebay and one of the main DD sellers.
  12. Lepke, Feb 20, 2016
    #12
    Lepke

    Lepke Member

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    I run 671 naturals in an 83' wood yacht. I burn a little over 8 gallons/hour @ 10 knots. At 8 kts is noticeably cheaper to run, but never checked it. Speed is expensive. Take the rpms down if you want economy. Run at 80% or less HP.
  13. g collis, Feb 27, 2016
    #13
    g collis

    g collis Member

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    I always love the fuel economy questions. It's simple, lean on the go sticks and the fuel goes down fast. We just took our 55' hatt with 1271TI's over a 1000 miles. I tried to run around 10 knots. However in the ICW the water depth averages around 10' and I would have to run around 1300 to maintain my 10 knots. Once the water got deeper I could feel the bow go down and could pull her back to 1000rpms to achieve my 10 knots. When it was all said and done I was burning 10 gal an hour running both motors and the gen set at 10 knots, props are 32x30. At 1800rpm we are going 18 knots. Fuel burn was 58 gph. My boat seems to like 1800 rpm.