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Thread: locking converter in 3rd worth any ET???

  1. #1

    locking converter in 3rd worth any ET???

    is locking the converter in 3rd worth anything in the 1/4???
    my converter is built for WOT locks....

    i dont really care about mph, on ET drops.
    04 Carbon Metalic GMC SIERRA ECSB- 5.3L, 3.73 locker, loaded
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  2. #2
    Senior Tuner
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    Depending on the (in)efficiency of the converter you
    could see 10-30HP from it, but you might benefit more
    from torque multiplication and higher RPM, than lower
    RPM and efficiency. You'd have to try it both ways and
    see what the timeslip says. And of course the timeslip
    for most of us ends before 3rd gear does; you might like
    top end locked for events greater than 1/4MPH for other
    reasons, like heat.

  3. #3
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    YEs its worth it. I lock em about half way through third. Even better when the juice is added. Try some killer MPH's. I gained 10mph with 100 shot.

    Rick

  4. #4
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    For that matter you might also gain by locking 2nd, since
    that takes you almost to half track.

    Where to put the lockup point, I guess is the interesting
    question. You'd want it to be where the locked RPM is
    above your shift extension RPM, for sure (presuming you
    had that where you wanted, on purpose). Something like
    75% of your upshift MPH, maybe?

  5. #5
    Quote Originally Posted by jimmyblue
    For that matter you might also gain by locking 2nd, since
    that takes you almost to half track.

    Where to put the lockup point, I guess is the interesting
    question. You'd want it to be where the locked RPM is
    above your shift extension RPM, for sure (presuming you
    had that where you wanted, on purpose). Something like
    75% of your upshift MPH, maybe?
    shift ext. is about 5300 as I shift at 6300. mph after shift ext is 85 or 90 mph. I dont remember which one. that is going into 3rd.
    what do you mean 75% of my upshift mph??
    04 Carbon Metalic GMC SIERRA ECSB- 5.3L, 3.73 locker, loaded
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  6. #6
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    Well, obviously locking right at upshift MPH would be no
    help at all, and locking at the beginning of gear would
    probably lose you some helpful torque multiplication.
    If you'd upshift 2-3 at 80MPH and enter 2nd at 40MPH,
    75% of 80 would be about 60MPH in your TCC lock MPH
    table. But this is just a notion, for discussion.

  7. #7
    Quote Originally Posted by jimmyblue
    Well, obviously locking right at upshift MPH would be no
    help at all, and locking at the beginning of gear would
    probably lose you some helpful torque multiplication.
    If you'd upshift 2-3 at 80MPH and enter 2nd at 40MPH,
    75% of 80 would be about 60MPH in your TCC lock MPH
    table. But this is just a notion, for discussion.
    60 MPH would be between the 2-3 shift... I dont need the trq multiplication on the 2-3 like I do on the 1-2 upshift??

    wow, this stuff is confusing
    04 Carbon Metalic GMC SIERRA ECSB- 5.3L, 3.73 locker, loaded
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  8. #8
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    Quote Originally Posted by jimmyblue
    Well, obviously locking right at upshift MPH would be no
    help at all, and locking at the beginning of gear would
    probably lose you some helpful torque multiplication.
    If you'd upshift 2-3 at 80MPH and enter 2nd at 40MPH,
    75% of 80 would be about 60MPH in your TCC lock MPH
    table. But this is just a notion, for discussion.
    Total newbie here, so apologies in advance for any stupid questions. You said obviously that locking right at upshift would be no help at all...why is this so? I have been thinking about doing just that, to get a little "bump" in the 2-3 shift. Currently, the 2-3 shift at WOT is pretty weak, and the car nose dives ('04 Vette coupe, H/C).

    I feel kinda stuck between options here because I was thinking I could either:

    - Drop to another gear, 3:42s or 3:73s to try and get a better 2-3 transition. The problem with this idea is that I fear complete loss of traction in 1st and 2nd, as they are already pretty slippery with my 3:15s.

    _OR_

    - Keep the 3:15s for 1st and 2nd traction, and do something about 3rd gear. It just seems like the 2-3 shift robs me of momentum, which is why I am considering the lockup just shortly after the 2-3 shift, or during the 2-3 shift.

    greg

  9. #9
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    Locking right before upshift might let you stay in gear
    through the traps but with 3.15s you're talking, what,
    130+ MPH for the 3-4? Congratulations, if that's your
    problem

    What we're talking about is, improving the delivered
    HP to move the mass, by changing from high slip to
    hard coupled across the mid-high RPM band all down
    the track (or some portion).

    Now, a well designed converter should deliver you
    an efficiency loss that is more than offset by being
    at a higher RPM, higher torque position in the power
    band. For example, if your converter is 100% efficient
    locked up, and you have a flat torque band at 350
    lb-ft and you're at 4000RPM in the moment, you
    deliver 350lb-ft*4000RPM/5252 = 266HP.

    Now let the converter unlock, and slide you up to
    5300RPM but at an 85% delivered efficiency. You
    get 300HP out the back, a bonus of 34HP. So you
    are better off unlocked (presuming your torque is
    indeed flat, which in an airflow limited machine is
    not to be taken on faith; you have to go by the
    results, in acceleration of mass).

    At some point in the powerband the converter will
    start costing, rather than improving, the delivered
    power. I guess this is where you'd like to flip it to
    locked. I think you want to see acceleration vs
    MPH, rather than acceleration vs RPM, to decide.

  10. #10
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    And that is why its most important to match a converter to power band of the engine.