I got it so HOT , it runs better than ever

Discussion in '6.9L IH & 7.3L IDI Diesels' started by mexicanjoe, Dec 2, 2018.

  1. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Either your speedo is wrong or you have 4.55s, I’m at 83 mph in fourth at the same rpm, and 106 in 5th in at the same rpm
     
  2. Grady J

    Grady J Registered User

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    How hot do they need to get for this to happen?
     
  3. Danielle

    Danielle I'm kind of not allowed any more trucks! Supporting Member

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    My truck lives on side roads. So when I drove it to the rally, it was the first time I had had it on the highway and it had never run better than when we got to the rally and back! When I tow on the highway I drive so grandmotherly that it doesn't count haha
     
  4. nelstomlinson

    nelstomlinson Full Access Member

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    On the big Cats at work, we try to get the EGT up close to 1,000F for a half an hour. That's measured at the end of the manifold, not right at the head.
     
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  5. Cubey

    Cubey Full Access Member

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    My 87s speedometer is off about 3-5mph with the stock 3.55 and stock 235s (250HD).

    I had a 91 Corolla that was about the same in being off. Pretty sure a 78 Dodge van I had was the same too.

    I guess they all used the same parameters to calibrate mechanical speedometers.
     
  6. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    Well what the deuce... maybe YOU have airplane gears! ;)

    I'll jack up one side and figure it out for sure then. If I do have abnormally short gearing maybe that's why reverse with a trailer(especially up hill)doesnt bug me in the ZF like it seems to bug others.

    And the speedo works good, I've checked it with a GPS.
     
  7. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    That's for cleaning deposits? Or DEF system? Is this driving or stationary?
     
  8. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    I’ve got 3.55 and 33” tires, but the old shop truck had stock sized tires and a 4.10 rear and would bury the speedo in fourth when the clutch wasn’t slipping
     
  9. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Back in the mid 90's, a friend and I had an impromptu race down the highway. He was in his 1989 F250, Ex cab, 4x4, ZF5, 235/85R16 tires. We ran down the highway as fast as we could go. I pulled out and went around him at about 105. My 75 F150, 4x2, C6, powered by a 1971 429 had more top end so I won that race. His truck would run 2100 RPMs at 60 in 5th so I am fairly certain that it had 4.10s in it.
     
  10. austin92

    austin92 Full Access Member

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    I don’t have a tach but I know I can run 80 in 4th. 245/75r16’s and 3.73’s


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  11. austin92

    austin92 Full Access Member

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    [​IMG]

    This is rpms for a zf5, 235/85r16s, and 4.56’s.

    Look familiar josh_bear?


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  12. The_Josh_Bear

    The_Josh_Bear Full Access Member

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    Why, yes it does!
     
  13. austin92

    austin92 Full Access Member

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    You sir have 4.56 gears lol


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