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46 post with 6-71 450hp

Discussion in 'Post Yacht' started by BigChief, Jan 9, 2020.

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  1. BigChief

    BigChief New Member

    Joined:
    Sep 3, 2018
    Messages:
    8
    Location:
    CT
    Can anyone here with the 46 with the detroit 671s tell me how it runs and what you think of the boat with this setup?
  2. Soulstice

    Soulstice Member

    Joined:
    Apr 1, 2013
    Messages:
    65
    Location:
    Portsmouth, Ri
    Is it a Mark I or Mark II hull? I believe some changes were made to the 46’s hull design over the years
  3. B Dickinson

    B Dickinson New Member

    Joined:
    Apr 8, 2018
    Messages:
    22
    Location:
    Maryland
    Big Chief - I had a 1985 46 Post with 671TI @ 450HP each for sixteen years. This is the "old" hull, NOT the newer hull that started around 88. While this hull/engine combo was considered good when the boat was built, she was no speed demon! Detroit/JT recommended a 2250 cruise RPM which would yield about a 22-22.5 knot cruise speed. I never ran them that hard opting for a 2050-2100 cruise RPM yielding a 20.5-21 knot cruise speed at around 31 GPH total. Never had the dreaded "Post death roll" in this boat with a straight on following sea but things would definitely get nautical with a stern quartering sea. Sold the boat with around 1900 hours on her and low cylinder compressions on both engines came up just fine. Later versions of the same boat with the "new" hull came out with 671TIB (485 hp) and 692 (55o hp). New hull 671TIB boats were somewhat underpowered at recommended cruise RPM while the new hull 692 boats performed well at recommended cruise RPM at around 25 knots. Downside running the 692's at "recommended cruise" was major overhauls at around 1600 hours - to the dismay of one of my buddies who bought a brand new 46 in 88 with 692's and had to have them majored @ 1600 hours. For us our bucket list boat was the 50 Post which we now have. Generally, if you talk to most Post owners like us, they will tell you they are great boats and that they love them!!! Just my two cents! If you are looking for a Post, good luck with your search!
  4. boatpoor

    boatpoor Member

    Joined:
    May 4, 2016
    Messages:
    52
    Location:
    32407
    I never ran one of the older 46 hulls, but we have a 1993 with 6v92's that we've put several thousand miles on with no issues. We cruise around 1800 rpms at 20-22 kts burning about 38 gph with a clean bottom. We have 2700 hrs on the engines and still running strong which is somewhat unusual for these engines but we took 2'' of pitch out of the wheels right after we bought the boat which unloaded the engines considerably. The 671 is overall a much better engine but at 485 hp it won't last any longer than the 6v92 in my opinion.
  5. B Dickinson

    B Dickinson New Member

    Joined:
    Apr 8, 2018
    Messages:
    22
    Location:
    Maryland
    Totally agree with your 671TIB 485 assessment UNLESS they have had new cylinder kits which gives them the ability to run up more hours. While I am no expert and can only speak from the experiences that I have had, I would surely bet that your unloading your 692s and NOT running them at recommended cruise RPM (which I think was around 2200) is why you are enjoying such good service from them. Awesome!! Have another buddy who is running 692s in a 45 Viking. He, like you, does not run them hard and has had good service from them - getting close to 2000 hours.
  6. RT46

    RT46 Senior Member

    Joined:
    Feb 22, 2011
    Messages:
    1,018
    Location:
    Long Island, NY
    I have the 46 with TIBs
    I am very happy with the boat overall
  7. cleanslate

    cleanslate Senior Member

    Joined:
    May 29, 2018
    Messages:
    481
    Location:
    Cherry Hill, NJ
    Good read and always makes good sense; IMO and experience ALL marine engines from gas to diesel run better and much longer when not pushed hard or to factory ''specs''...remember the parts business is a BIG part of the engine makers. They want you to break things and help support their dealer network with repairs and sales. I run my 471TIs 1600rpm, if I'm in a hurry 2100 rpm. But I'm on the boat to relax and not hurry, so it's mostly 1600.
    My gas Crusader 350; 3200/3600 rpm...still a clean and mean 2001 engine no oil burn etc.