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Thread: 8HP70 Maximum Torque Generation at Launch

  1. #1

    8HP70 Maximum Torque Generation at Launch

    Has anyone tried to launch a car with the converter actually unlocked through all of 1st gear? Or launch in "slip" and max slip out to 200 rpms?

    In both Sport and Track mode, converter lockup happens at a pretty low rpm (1000-1500) in 1st.... with overlock occurring in Track mode. Most cars with a decent cam are idling at 800-850, so the converter locks essentially as soon as the throttle is pressed.

    To me, this nullifies any potential torque multiplication from the converter since output shaft speed is almost immediately forced to 1:1 with engine rpm.

    Or....perhaps raise lockup above the converter flash?

    I understand why Dodge locks it up (longevity)...but my understanding is the greater the difference between output shaft speed and engine rpm, the greater the torque multiplication effect.... at least up to a point.

    Ideally we could then lock it up after the 60'.

    I'm also going to play around with lockup at peak rpm in higher gears (4-5 shift). In Track mode, with Overlock, recovery rpm is 5500 rpm off a 7k shift. It seems that a little slip on the shift would increase the recovery rpm.

    I do know Dodge uses a different slip time strategy with 8HP70 for the 1320 cars. They actually dramatically increase upshift slip times to around 400ms in Max mode. I had read they learned the Demon was actually faster with longer slip versus less and they carried this data over to the 1320.

  2. #2
    Just turn off the clutch in at least 1st-3rd and see how you like it. its an easy switch back and forth.

    On a NA car it makes sense to get the RPMs up and also take advantage of the TC torque multiplication.

    I think Boosted cars its a bit different story. They're usually traction limited already and can't make use of the higher stall RPM, so their clutch comes on early. I think the Demon 8HP90 stall is around 1800, where a the HP70 is closer to 2000

    Quote Originally Posted by kenandjenn4551 View Post
    In both Sport and Track mode, converter lockup happens at a pretty low rpm (1000-1500) in 1st....
    Remember that rpm is Output shaft speed not engine RPM. So 1100rpm OSS in first gear is ~5200 engine rpm
    Last edited by duster360; 04-23-2021 at 02:42 PM.

  3. #3
    Advanced Tuner
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    Are you logging lockup?

    I tried it with it unlocked completely in 1st and 2nd a year or two ago.
    If in doubt, multiply everything by 1.1.