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crawl ratio vs stopping ability

Discussion in 'The Garage' started by BranndonC, Dec 11, 2004.

  1. BranndonC

    BranndonC 3/4 ton status

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    is 57 to low of a crawl ratio for a truck to be able to have the brakes actually stop it, i mean its an automatic, so double it and you have 114. the truck has 550 or so ft #'s of tq and disc brakes all around with a 1 ton master cylinder.
     
  2. sled_dog

    sled_dog 1 ton status

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    as usual I'll be the guy who asks what setup you are running to get 57:1 ratio. TH400 with 5.13s is 50.89 and 700R4 with 5.13s is 62.79. I have no experience with stopping this setup so I'd like to know as well. My plan is 700R4-doubler-5.13s so mine will be 62.79:1.
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    The 2x thing has been beat to death and is total hogwash. There is no additional torque applied to the wheels because the torque converter is slipping.

    At 57:1 your rig will crawl and stop just fine.

    You'll likely want more crawl ratio unless you have a super low stall converter.
     
  4. BranndonC

    BranndonC 3/4 ton status

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    the set up i'm thinking about can be seen here
    http://coloradok5.com/forums/showthread.php?t=123101
    its th400 with a 3:1 203 and a 2:1 205 and 4.10's
     
  5. Hossbaby50

    Hossbaby50 3/4 ton status

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    With a 36:1 crawl ratio with my 700R4/208/4.56's it can be hard to stop. I know that most of the guys here in AZ with doublers and 4.10's have a pretty hard time stopping sometimes.

    If my motor is turning 900+ RPM's it will overcome the brakes with only 36:1 crawl and a mild TPI350. I have a low stall converter in my truck. I do not have disc rears though.

    You will have a very hard time stopping with 50:1 crawl with a large torque motor if you have a decent idle RPM. My idle is 700RPM and my truck will stop but not well.

    You will want to run as low on the idle as you can and run a converter with a stall of a 1000 or a little higher.

    Harley
     
  6. ntsqd

    ntsqd 1/2 ton status

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    Perhaps you can explain why the FSM (that would be the Factory Service Manual) for my Grandad's GMC Motorcoach LISTS the torque multiplication ratio of the TH 425's Torque Converter as being 2.6:1?
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Instead of quoting from a book, why don't you just tell me how a slipping torque converter is multiplying power?
     
  8. sled_dog

    sled_dog 1 ton status

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    thats easy. for ever 2 revolutions of the crankshaft, the input shaft on the transmission rotates once. Sure sounds like reduction in my book.

    if you want to say that, the reduction doesn't "increase power"(bad term more like making use of whats there), then put a 2.73 R&P in your diffs and call it good.

    and you have nothing to back the idea that it doesn't work like that. Where as those who think it does have books(from GM) and plenty of info from respected transmission companies.
     
  9. sled_dog

    sled_dog 1 ton status

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    I just commented on Torque Multiplication to a buddy and he made a VERY good analogy. Tractor Pulling. Ever seen a tractor puller? They don't grip and grunt through a pull, they get wheelspeed and friction pull. The friction of them tearing away at the ground moves them forward. Not fast but it does it better than slow wheel speed. Think of 2 halves of a torque converter doing the same thing. Think of one as the tractor tire and one as the ground.
     
  10. 84k5

    84k5 1/2 ton status

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    For a basic fluid coupling you are correct...you can't multiply torque. You have the same situation as with a standard's clutch. However modern torque converters are not basic fluid couplers because of the stator in between the turbine and the pump. Torque is multiplied by accelerating the fluid in the torque converter. The exact flow process is a bit beyond my understanding(only taken one fluids class!); I can't even imagine analyzing that flow on paper. Anyways, the accelerated flow generates a larger force on the turbine output shaft, thus multiplying the input torque.

    It is somewhat counter intuitive to think of fluids multiplying torque, but you shouldn't claim something as truth when you really have no clue, as you clearly have not studied the subject at all. Did you think autos have half the first gear of standards for no reason???
     
  11. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Gears DO multiply torque, but there is an established mechanical fact as to why they do so.

    A slipping clutch, or torque converter, is actually losing power, which is dissipated by heat.

    Input torque + slippage = lesser output torque + heat
     
  12. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Sounds interesting, but also denies the law of phsyics as we know it. I would like to hear more about this, though.
     
  13. 84k5

    84k5 1/2 ton status

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    Please state the law it denies.
     
  14. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Energy cannot be created or destroyed, only change form from one to another.
     
    Last edited: Dec 11, 2004
  15. 84k5

    84k5 1/2 ton status

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    Why you're at it, please tell me why an auto has half the first gear of a standard.
     
  16. 84k5

    84k5 1/2 ton status

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    It is no different than multiplying power using gears. Don't deny what you do not understand.


    A good comparison to prove your point wrong is a garden hose. You put your thumb over the end and you accelerate the fluid. A pump that can only push fluid x ft/s through the hose has its 'power' increased in this way as the fluid can now travel several times faster than x.
     
    Last edited: Dec 11, 2004
  17. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The 2X factor of the torque convertor is only good until stall has been achieved. At that point your magically deep crawl ratio is replaced with something a little more real world.

    My crawl ratio is 58.45:1 at idle through redline unless I shift into the next gear. Branndons set-up might be 57:1 at idle, but by 1400 rpm or so it's half that.

    Rene
     
  18. sled_dog

    sled_dog 1 ton status

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    no Rene, his will be 57:1 before torque converter multiplication.
     
  19. 84_Chevy_K10

    84_Chevy_K10 Banned

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    False. When you place your finger over the end of a garden hose, you create resistance to flow that increases pressure. in order to move the same volume through the small hole, pressure must increase. No energy is disipated in any other form here, except in the swelling of the hose because of teh increase in pressure, which is minimal.

    A torque converter is totally different. It is disipating energy (read power) as heat before it stalls.

    An auto has half the 1st gear of a manual because the creeper gear is only there to get you rolling when you have a heavy load, without burning the clutch as much. An auto doesn't need to burn the clutch because it can slip the torque converter. Although no additional torque is provided to the wheels, it can raise engine RPM through slippage which increases the amount of torque that is immediately available to get the load moving. No matter how much the torque converter slips, it will never be able to get the load moving like a 6.55:1 creeper gear, but its sufficient.

    I am not anti-auto by any stretch of the imagination. In rock crawling, the autos are dominating. I personally prefer a manual, but I recognize that both can do the job. The burning of the torque converter does allow you to achieve a level of control similar to having increased crawl ratio, but it does not increase the amount of torque applied to the wheels in my opinion.

    A slipping clutch doesn't increase torque, either....but it allows you to travel slower just like that slipping TC.
     
  20. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    LOL, guess I read that too fast...:doah:

    Rene
     

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