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Thread: LFX auto for Autocross & HPDE

  1. #1
    Tuner in Training
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    Feb 2018
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    LFX auto for Autocross & HPDE

    I haven't driven an automatic, except in a luxury car, for quite some time now but I believe that if I transplant an automatic transmission with the LFX into my Lotus 7 like car it will be quite adequate for Autocross, HPDE and the occasional NASA 1 hour race now that the transmissions don't do that hard jerk when downshifting that upsets the backend. They feel more like a good manual downshift.

    I think the auto would be simpler to find and I'm thinking it might even be (a little) less expensive.

    I have no idea which transmission is used in the Camaro, CTS, etc. only that it is either a 6 speed or an 8 speed. I can't believe that in this day & age an automatic in a performance vehicle wouldn't hold up to that little bit of abuse. It's not as if I'm going to use the car in the 25 hours of Thunderhill or 24 hours of Le Mans.

    What do you guys say? And what changes to the software would you recommend?

    I have a CTS with the auto and I found out that when you are in manual mode it will still downshift when you're going slow enough rather than stay in the gear as I'd like. Can that be tuned out? I'd like it to stay in the same gear unless I came to a complete halt as does the BMW trans.

    Can it be made to shift a little sooner after you move the lever? I found the one time I tried to drive the CTS a little hard to see what the transmission would do that there was quite a lag there. Can that be reduced? It would make sense it could be adjusted on the upshifts but maybe the soft downshift would still require the time. Downshifting wasn't much of an issue.

    Are there any upgrades any of you would suggest or are there better models than others I should search for before I buy a trans?

    I have decided that I am not going to buy the software. I don't want to take the time to learn the software which will take time away from my build. I'd rather pay someone else to do this.

    I am in the Fort Worth area so is there anyone you might suggest in that area who could do the trans tuning?

    David B.
    "mobilito ergo sum"
    I drive, therefore I am.

  2. #2
    Tuner in Training
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    May 2018
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    I have just completed an LFX/6L50 transplant into a Miata and have tried an Autocross.

    Here are some particulars. Paddles ar inop at present. The reason for this is that the paddle shifter in the Camaro worked through the BCM and I was attempting a hardwire replacement. Appears to be a software issue.

    This means the only modes available are Drive and Sport. Without paddles, it is impossible to manually control gear selection. While shifting performance is quick, double downshifts occurred during the run. Downshifts and upshifts occur when you would stay in the same gear with a manual transmission. The ability to manually control gear selection is highly desirable and I would say essential to be competitive.

    Hardwired paddles are supposed to be available with these ATs but reports to the various forums indicate spotty results.

  3. #3
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    Boy you got this to me just in time. I've been watching Copart for a CTS but most of them are auto and I'd just about decided I'd let the right car decide the transmission I was going to use.

    i'm with you and recognize the need to be able to manually select the gears. I assumed it was as easy as transplanting the paddles.

    How much wider is the Automatic than the manual trans?
    "mobilito ergo sum"
    I drive, therefore I am.

  4. #4
    Tuner in Training
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    Jul 2012
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    If you can get it to fit (crossmember, driveshaft, yoke, converter etc.),
    get a good calibration setup on the trans,
    and get some of the oem take paddle shifters to work on your steering column like us g8 and SS guys do;
    Then go ahead and find a 6l80e and 6l90 (might be hard) and do it. That trans can be setup for super quick and responsive shifts with the right setup, whether or not you use the paddles.

  5. #5
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    djwarner, do you have any leads on what module or software that might be necessary for the full manual operation?

    thewrx, I am currently looking for a complete car on Copart so I can get anything I need off of it. After autocrossing my CTS there's no way a non manual shift option would be acceptable for anything other than street use.

    I haven't heard the 6l90 moniker, what car does that come in?
    "mobilito ergo sum"
    I drive, therefore I am.

  6. #6
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    The 6L90, 6L80, 6L50 and 6L45 are a family of GM ATs that supposedly have the same electronics and hydraulics and only vary in the torque capacity of the gears. The 6L80 and 6L90 are found on the 2010-201? Camaros with V8 engines (higher torque means bigger gears that means bigger housings).

    Again these transmissions have been produced for more than 10 years and I imagine there has been some mechanical and electronic changes over that time. There are three forms of manual shifting - hardwired paddles, paddles through GMLAN, and mechanical input through the shift lever. I have not resolved my issues as yet though my research indicates promise. So I won't tell you what to do. I have heard of 6L80 with similar problems.

    I would not try to include the BCM as part of a work around as it gets very finicky about security and demands to hear form all kinds of other control modules that are not installed.

  7. #7
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    I know this is a bit old, but.. I am currently trying to configure the LFX 6 speed auto to run through Miata paddles and floor shit. I just finished a GM crate engine/ 6L80e swap where I successfully used all the Miata controls, i.e. floor shifter and stock steering wheel paddles to operate everything as GM intended without a bcm. Drive on the shifter gives full automatic control. The next position down, sport if you will, is still fully automatic but more aggressive. When you are in sport mode ,any time you touch an up or down paddle it goes into tap up/tap down mode. You have full manual control over the gears (to a point, it won't let you over rev going up or down) and it auto matches the downshifts. I'm going to try the same methodology for the 6l50e and see if that will do the trick. DJwarner, i sent you a couple pm's. Thanks.

  8. #8
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    A Paddle shifter setup that works

    The 6L50 is in the same family as the 6L80/90, however, the software for the 6L50 does not use the hardwire input. Paddles have to be input through the GMLAN. Needless to say the GM BCM is less documented than the E39 and I know of no one using it in a swap.

    I did find a third party who has created a BCM simulator that has successfully implemented the paddle functions. It was designed for the E38 ECU but we have gotten it to work with the E39. It also interfaces with the cruise control on the E38, but we are still troubleshooting why it won't work with the E39. It appears that the E39 is a hybrid with some Gen IV and some Gen V interfaces.

    www.oecontrols.com

  9. #9
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    I just found this article that explains a lot about the E39 theory of operation. It explains while some have had problems setting the rev limiter and why tuners are seeing differences in accelerator pedal input and throttle body position. It also points the way to a new tuning strategy.

    https://www.hptuners.com/help/vcm_ed...vanced_e78.htm