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Torque Converter Fun

Discussion in 'Early CJ5 and CJ6 Tech' started by cjsammyowner, Oct 2, 2017.

  1. Oct 2, 2017
    cjsammyowner

    cjsammyowner Member

    Paxtonia, Pa
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    Jan 4, 2009
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    Hi all. Been awhile since I've worked on this Jeep of mine. I have a question about 225 buick and th350 torque converters. I have a stock chevy 350 v8 converter, an aftermarket 12" converter but have no idea which stall speed, and a th400 converter from a cucv with the 6.2 diesel, which I believe has a 1250 stall speed. The 225 is factory stock. So my question is which stall speed in a torque converter works best with a stock engine, th350 and 3.73 gears. Thank you.
     
  2. Oct 2, 2017
    Dauntless1971

    Dauntless1971 Member

    Bend, OR
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    Oct 22, 2004
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    The smaller the torque converter is the higher the stall speed will be.
     
  3. Oct 2, 2017
    cjsammyowner

    cjsammyowner Member

    Paxtonia, Pa
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    I do understand the size of the converter is a tell tale sign of the stall speed, however I have no clue what stall speed matches the power/torque of the dauntless 225.
     
  4. Oct 2, 2017
    Dauntless1971

    Dauntless1971 Member

    Bend, OR
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    Oct 22, 2004
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    New ones are not to expensive. I have always had issues installing used ones unless they were never left out of the transmission after removing. I think you would be better off to run the 350 one. If the 400 converter is 1400 rpm stall stock with the 6.2 you can expect to have an even lower stall behind the 225.
     
  5. Oct 2, 2017
    Twin2

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    Virginia Beach, VA
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    when I had the auto in jeep . I ran a 1200 rpm stall . just because it idles at around 875 rpm . and it was recommended by shop that put shaft kit in transmission . buy new
     
  6. Oct 3, 2017
    Dauntless1971

    Dauntless1971 Member

    Bend, OR
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    Oct 22, 2004
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    The 400 converter may also be a larger bolt pattern. I think the stock converters for the 225/231 had a stall more like 1700-1900. And the 400 thm would of been like you say closer to 1200-1400. For off road use I bet you would do better with a lower speed as Ron said he once did. Just did not say how it worked for him.
     
  7. Oct 3, 2017
    Twin2

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    Virginia Beach, VA
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    It ran just fine . like any other automatic . unless foot was on brake . it would creep . I did a tub repair and shortly after painting jeep green again . it just didn't feel like . the jeep I had bought many years earlier . the only reason I went through all the trouble to install it . was I had blown up four T14's . well the son took out the last one . learning to drive . as we all know the T14 is weak . the auto made jeep alot quicker off the line to say 45mph . daughter drove it a few times to learn how to drive too . auto . she was shocked to find out I put a stick back in it :rolleyes: but she doesn't drive it anymore anyway
    I only have one picture of auto in frame . like any conversion it takes alot of thinking to make it work , cross member/shifters/driveshafts/oil cooler
    jeep floor 6.jpg
     
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  8. Oct 4, 2017
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    You might look into Chevy Vega/Pontiac Astre tranny parts also. They used the same torque converter. flex plate and TH350 bolt pattern as the Chevy/Buick v8s did. I do not remember the stall speed, because it has been quite a few years since I owned and drove one. I do remember they were interchangable.
     
  9. Oct 5, 2017
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    The Vega converter (for the few years a TH350 was available in a Vega) is a fairly high stall. Back in the day, the Vega converter was the hot setup in Chevelles and Cameros because there were not so many aftermarket choices available. If I recall, it was around a 2300/2400 rpm stall speed.
    -Donny
     
  10. Oct 5, 2017
    timgr

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    Medford Mass USA
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    How is the stall speed relevant to trail driving? I have an idea what it does on the street, but say you are two-footing it through the rocks - what effect would the stall speed have? I'd think high-stall would give you more torque multiplication at low speeds, and two-footing would be made more effective.

    I asked an SX4 owner about this, and he said that with an automatic, he would often stall the car on the trail, even when two-footing. This suggests to me that the SX4 has a low stall convertor, which would help with economy but make power less available at low speed.

    I'd think the first constraint would be to look at your cruising RPM on the highway. You would not want the stall speed any higher than that. Stall speed changes with engine torque, so if you hop up the engine or use a convertor from another application, actual stall speed will be different from stated stall speed. Then I'd consider whether I wanted the exciting feel of high stall around town, or better economy. I'm just speculating based on what I understand - plese feel free to correct and expand.
     
    Last edited: Oct 5, 2017
  11. Oct 5, 2017
    Dauntless1971

    Dauntless1971 Member

    Bend, OR
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    This was out there in the web. I have found lots of charts for street drag racing not so much for off road use.

    Two commonly asked questions about torque converters and off road driving are:
    1. What kind of torque converter should I get for off road driving and why? And,
    2. What is the significance of the "stall" speed.
    For off road driving, you want low stall. Exactly what number depends on what kind of engine torque you've got. If you've got a torquey engine, you can get a tight converter. If you're rock crawling, you probably have a torque monster engine already. If you're not rock crawling, it doesn't' matter a whole lot other than what you prefer.

    Something with a stall speed of around 1600-1800 would probably be the best bet.


    OEM converters are usually low stall, and probably good for most applications. You can determine your convertors stall speed by pressing hard on the brakes and with the transmission in drive, push on the gas and note the highest rpm achieved.
    High speed stall convertors are used by drag racers since they allow the engine to climb higher up into its power band before fully coupling with the drive train. It is very much like revving up your motor and dumping the clutch.

    Disadvantages of a high speed stall converter for off road driving are:
    Greatly increased transmission heat. The slipping at low rpms will create gobs of heat.

    Worse gas mileage since driving below the stall speed is much like driving around in low gear.

    More difficult to moderate speed.

    A lower stall is easier to moderate since it starts to engage without having to get your rpms up very high. If you have to get the rpms to up over 2000 before you start moving that's a bit of pedal you're applying. Once you start to move at this rpm, you may run into objects, break axles or other bad things could happen.
    For street and highway driving, you want your converter's stall speed to be lower than your cruise RPM. Significantly more heat is generated below the stall speed than above it, so if you have a 2500 stall converter, and you cruise at 2000 RPM, you'll generate too much heat, which breaks down the transmission fluid, and that ruins transmissions.

    A high stall converter will slip more at highway speeds than a low stall converter, but probably not much.

    When your engine accelerates, and your RPM is below the stall speed, the fins on the engine side of the torque converter are moving significantly faster than the fins on the transmission side. This allows the converter to "slip," much like a clutch, but it also creates turbulence in the fluid, which is what generates the heat. The rotating fins on the engine side cause the fluid to rotate, which in turn puts force on the transmission side fins causing the transmission to turn. Imagine spinning your hand in a bucket of water. At first there is turbulence, but eventually the water is moving close to the same speed as your hand. If there is something at the bottom of the bucket, it begins to spin as well.

    A car with a high stall converter is really not much fun, except for racing. At low RPM, your engine feels a little mushy. The engine tends to wind up to the stall speed before anything happens, and then it stays at that RPM until your car catches up to the engine speed. If any shifts occur during that time, you barely even feel them (of course this can be good if you've installed a shift kit).

    I would consider 2000 RPM and below reasonable for the street, 3000 and above unreasonable, a the rest depends on the vehicle.
     
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