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Thread: Locking Converter Early?

  1. #1
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    Default Locking Converter Early?

    Well I have done all I could with DFCO and picked up 1 mpg consistently on the highway. Im now thinking of locking up the converter in second third and forth. Can you please provide pros and cons of doing this. Will the converter clutch wear faster - will there be any harm in doing this - Please advise.

    Thanks
    2002 GMC Sierra ECSB
    Turbonetics T7675 6lbs boost, 42lb injectors, Single 4 inch exhaust with Hi-Flow Cats, 6.0 swap, Comp Cam LS9 Cam, EFIlive Tune, E-fans, Snow Performance Meth Kit, soon to add KB Boost a Pump,

  2. #2
    Lifetime Member Mr. P.'s Avatar
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    What converter is in the truck now?

    Mr. P.
    2003 Silverado SS, with Novi-1500 "CAI mod"
    EFILive V 7.5 COS-3 (OLSD, for now!)

  3. #3
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    I currently have mine locking in third and obviously fourth. I like the fact that it locks in third now, being that it isn't in OD the truck is still really responsive. The pro is better mileage and lower rpms (stock 6.0 converter with 4.10s is too big imo, and mine is stock). I haven't had the time to figure out why it sometimes stays locked during the upshift while other times it unlocks (which is very annoying - rpms jump to stall speed during the upshift).
    It will wear the clutch faster - how much I am not sure. Another con is if you are like me, the stupid PWM valve is worn in the tranny. The easy fix for me was to increase the minimum tables, but when in third gear on very rear occasion, I can feel my truck "buck" a little when going downhill b/c of this.
    But overall I like it locking in third as to not. With that said however, with 4.10 gears and the speed limits of where I travel, it hasn't made enough sense to lock second - so I have no feedback for you there.

  4. #4
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    I've been thinking about doing this for a while. Wondering how low i can go. 3600 stall with headers and duals is kinda ridiculous sounding when i'm only going 20-30 mph.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by spy2520 View Post
    I've been thinking about doing this for a while. Wondering how low i can go. 3600 stall with headers and duals is kinda ridiculous sounding when i'm only going 20-30 mph.
    Depends on your cam... more duration/overlap needs lockup minimum speed to be higher to avoid surging/chugging...

    you have to see how low you can go and check engine behaviour.

  6. #6
    Lifetime Member swingtan's Avatar
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    Also....

    Locking the converter results in reduced slippage loss in the converter, which can help economy. However, it also,

    • removes the "torque multiplication" that the converter provides.
    • lowers the engine RPM, reducing manifold vacuum and pushing the ECM closer to PE mode.


    So while it can help, it can also hinder economy by loading up the motor too much. Sometimes, running a lower gear but locking the converter is better than running a higher gear without locking the converter.

    The 6 speed boxes in Aus. lock up in second and I've tried locking up in 1st which seems to be fine for light throttle. If you are going for every last bit of economy, you could also look at the pressures, but need to ensure you don't introduce any slippage when reducing the pressures.

  7. #7
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    cam is 236/238 .601/.605 on 113 lsa. economy would be nice but i just don't want to sound so ferocious when i'm cruising or on my way to work.

  8. #8
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    Is it even possible to have the converter lock in 3rd and remain locked as it shifts to 4th? I've been experimenting with having it lock in 3rd around 20-22 mph, then when it shifts to 4th a few mph later it unlocks and then locks up again. I've been playing with D0902, D0903, as well as D1001-1006. Making sure not to overlap apply/release curves. This is on a 99 LS1 pcm with 2002 OS.

  9. #9
    Joe (Moderator) joecar's Avatar
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    For durability of single plate TCC, it's best to allow it to unlock during shifts.

  10. #10
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    This is only for extremely light driving, like <12% TPS. You think it affects durability that much? If so, any suggestions on minimizing the time that it is unlocked? I'm thinking maybe lower the apply speeds, but disable locking during upshifts or something like that.

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