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Fuel economy detroit diesel 8v92

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

  1. aircar

    aircar New Member

    Joined:
    Aug 12, 2008
    Messages:
    11
    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

    Capt J Senior Member

    Joined:
    Jul 11, 2005
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    6,142
    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. rcrapps

    rcrapps Senior Member

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    Sep 8, 2004
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    2,031
    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

    Capt J Senior Member

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    Jul 11, 2005
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    6,142
    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. rcrapps

    rcrapps Senior Member

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    92s are cool, 71s Rule.

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