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Thread: Downshift time for multiple gear downshift 8L90E

  1. #1
    Tuning Addict WS6FirebirdTA00's Avatar
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    Downshift time for multiple gear downshift 8L90E

    I wanted to get some feedback, had issues searching and finding results.

    The only thing I could see was a few posts where people did not mess with multiple gear downshifts. For example, 8-6 or 8-4.

    I want to get rid of the horrible lag in downshifting, but wanted to see what was working for other/if there were any issues going much faster in multiple gear downshifts on the 8L90E.

    My thought was to go down about 10% and see how that does and then work areas of concern.

    Based on the table RPM axis, I also assume that is based on the current gear RPM - not the oncoming gear expected RPM?

    Also, what is the torque ratio? Current gear vs. oncoming gear predicted?

    Thanks.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  2. #2
    Tuning Addict WS6FirebirdTA00's Avatar
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    Anyone mess with these?
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  3. #3
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    My GM Transmission book that I bought from the Tunning school says don't mess with any multiple upshifts or downshifts so I didn't...personally I checked/modified each value by hand as opposed to using smoothing etc...I basically mimic'd my tow/haul mode aka pattern A but not as extreme...for example if pattern A said shift up @ 14mph I made mine 12mph etc...also important to make sure your downshifts are not too close to any upshifts...also made note of the fact that TPS 87.5 is really WOT so all values from 87.5-100 should be same value...mine shift's like a dream now & MPG actually went up considerably...I believe that is bc I am shifting in the meat of the power band & also bc DOD runs in 4 cyl mode more now than before the changes...I had noticed it ran in DOD mode more when using tow/haul/pattern A but the RPMs were too high for good gas mileage so I modified my normal shift mode. I might be comparing apples & oranges with tuning my 2018 GMC Sierra 1500 6.2L v8 but its the same tranny so hoping it helps!
    Last edited by douginnow; 06-11-2019 at 11:40 PM.

  4. #4
    Tuning Addict WS6FirebirdTA00's Avatar
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    Thanks, I was wondering more about times rather than speed. I have my speeds where I like them, but the long downshift delays are annoying. I wanted some feedback on what others have has success with before taking a risk that could adversely affect the trans reliability. I also have DoD disabled and saw my fuel economy increase with everything else I did in the tune.
    Last edited by WS6FirebirdTA00; 06-12-2019 at 04:06 AM.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  5. #5
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    The book advised me to change "all" my up/down shift times to 0.35s...however some of my OEM shift times especially 4-5, 5-6, 6-7, 7-8 were already lower than that (as low as 0.22s) so I took a different approach...any OEM shift time that was already below 0.5s I didn't change & any OEM shift time that was above 0.5s I lowered to 0.5s....a few OEM 1-2 & 2-3 shift times near the upper rev limit that were above 1s (some as high as 1.5s) I dropped to 0.75s but for the most part 0.5s was max. So in summary something to try would be: flash back to OEM shift times, then lower any OEM shift time that was above 0.5s down to 0.5s & any OEM value that is already below 0.5s leave it alone...food for thought! I can post my up/down shift files when I get a chance if it helps.

  6. #6
    Tuning Addict WS6FirebirdTA00's Avatar
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    Yes I have my tables all set up for the sign gear shifts just fine.

    The pain is if I am cruising in 8th and punch it, it goes something like 8-6, 6-4, 4-2. I have not touched those shift times as I don’t know if I can use a lower value safely/reliably. I started to tinker to get the 0.7/0.8 second areas down closer to a half second, just wanted some feedback on those specific table before loading.

    My single gear downshift time, upshift times and up/down speeds are where I want them. It is only the multiple gear downshift.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  7. #7
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    From 8th all the way down to 2nd gear? ...wow! I don't let mine shift into 8th until 50mph at 0% TPS so it can't down shift that far...my 2-3 upshift maxes out at 27mph (& max speeds are similar or just slightly lower than Table A)...maybe post your up/down shift & multi gear shift tables/tune for observation...sorry I couldn't be more help! Amazing that you're getting better MPG with DOD disabled...I have seen a few others say the same but most have said they dropped 2-3 mpg.
    Last edited by douginnow; 06-12-2019 at 05:01 PM.

  8. #8
    Tuning Addict WS6FirebirdTA00's Avatar
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    There is a small window it will go to 2nd. I shift to 8th right at 50 mph as well.

    The downshift is 2-3 mph lower than that at 0%, which may get into the window of the top of 2nd.

    Either way, from 6/7/8 down to low gear can be painfully slow.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  9. #9
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    Could you post up your tables for comparison? Doing the same for my 2016 Sierra 5.5 8spd.

    5.3/
    2016 Sierra Denali 5.3L - All stock but the air filter & GMPP Borla exhaust

  10. #10
    Tuning Addict WS6FirebirdTA00's Avatar
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    Sure will, just don?t have my PC on me at this moment.

    Here it is
    Attached Files Attached Files
    Last edited by WS6FirebirdTA00; 06-28-2019 at 11:36 AM.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  11. #11
    Tuning Addict WS6FirebirdTA00's Avatar
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    Added the file
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  12. #12
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    I've had my 2016 Sierra self tuned on all of the shift time tables for years now with zero issues. I staggered the tune on mine. The lower throttle input areas I left stock, once you get into the throttle I reduced the times by 20% (multiplied by .80) and then as I near the WOT point of the table I went with .60-.70. This way the truck drives near stock at really light throttle, once i get into it the shift times get quicker and then once I go WOT it really firms up the shifts.

    Doing so I have never messed with the pressure tables and the way it sits it will bark the tires on the 1-2, 2-3, and the 3-4 shifts.

  13. #13
    Tuning Addict WS6FirebirdTA00's Avatar
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    Can you share your tables?

    Also, what is the torque ratio? Not sure if it is current vs. desired or what. Any insight would be great.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  14. #14
    From the small information we have on PIDs for logging the 8L90, I have not been able to tell what the transmission does at WOT downshifts. Yes we have the tables there that skip one gear, 8-6, 6-4, 4-2, etc but im not sure what the transmission is actually doing since we only have commanded gear which dosent tell much and only the off-going PID.

    However if you look at a ZO6 TCM tune you will see it has considerably faster shift times, you can paste these shift times in, but when I did it for my Camaro it started binding up especially on the WOT to 3rd gear downshift that it would trigger stabilitrac on.

    Yes the downshifts are horribly slow, but GM sure likes to advertise how fast there upshift is. But I think Doug is right, about the only option we have is to just not let it upshift so early at part throttle and that way it dosent have to go up through as many gear when you go WOT.

    I also wonder if we can full flash the 8L90 TCM, it would be interesting to see if we could full flash the ZO6 TCM tune with the faster shift times, as far as I know there shouldn't be anything different in the ZO6 8L90 as opposed to the camaro and truck 8L90?

    I also wonder if there are aftermarket companies working on shift kits as well? I wish I had better schematics of the 8L90 to figure out what's going on, it seems like its a slow clutch volume having to fill up that's making the WOT downshifts take forever, and I would think its because they optimized it for fuel economy, so maybe it has something to do with the 2 stage pump or something? I'm not an expert in transmissions so just a guess?

    The 8L90 dosent do too bad at WOT downshifts to 3rd on the highway and even WOT downshifts to 1st, but the WOT downshifts to 2nd from 8th or 7th are painfully slow. There is also some times if you roll into the throttle instead of going WOT instantly, it can take 3-4 seconds before you get into 2nd gear, and by that time you've almost at redline by the time you get into second.

    I know its not really a solution but (and this is something we need control over in HP tuners badly, along with launch control settings), is WOT blip the throttle to get it into performance mode, then it will hold higher gears and should downshift faster since it dosent have to sequentially start from 8th to 7th to 6th to 5th ect. (I'm still not convinced it skips gears at downshifts)

    Hopefully someone with good hydraulic knowledge of the 8L90 will chime in.
    Last edited by cmitchell17a; 07-01-2019 at 09:56 PM.

  15. #15
    Tuning Addict WS6FirebirdTA00's Avatar
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    When you say binding up, what exactly was it doing?

    I don't want to change any upshift and ride at higher RPMs. I have been slowly tweaking the downshift. I compared to a 2016 8 speed truck and some of the tables were considerably lower. I moved towards them, but did not do a direct copy. I mainly lowered the higher RPMs and blended to the lower regions. Down low I may be 5-10% faster, at high RPMs some areas may be 20-30% faster. Some areas were as high as 2 seconds.

    I never see multiple gear upshifts, even though we have the tables. I notice on downshifts it seems to jump 2 gears, not sure I have ever seen 8-2. I have seen something like 8-6 and 6-3 or something like that, just trying to follow the commanded gear in the log. What I did made quite a bit of difference. Enough to be happy it is faster, but not so fast I feel I am risking anything.

    I need to find a Z06 or Camaro tune with the TCM file in it. The ones I downloaded did not have that.

    How long did you drive on the Z06 tables. I just wonder if the clutch fill preset values are different, allowing the Z06 to fill faster. I had some issues in the past on some shift flare between gears. I thought it was my changes, but it turns out as I drove it, it went away. The learning in these TCMs is what confuses me and makes me go back and forth if a change was good or bad. The more it learns, the fewer those little issues are.

    After my changes I tried to do some downshift figuring if it was too fast it would band a gear or hang up in between. I am interested to see other issues to know what to look out for. I did some coasting stops to see how it would downshift to make sure it would not be clunky. All seems well there from what I can tell so far. The multiple gear downshifts are tricky to get the high RPM areas. That is my only concern if I went too low there. I honestly don't think though that going from 2.0 seconds to 1.4 seconds would be terrible. Some tables are low and some are high, so it would be interesting to understand more about what/why they are like that. Like you said, understanding more about these internal can help understand why GM may have implemented what they did or help us identify other things we need to do it right. If we had more tables like the 6 speeds I think it would be obvious. I did request to support if clutch fill/adaptive tables could be added to the 8 speed. I am not sure they are there to add like the 6 speed had.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  16. #16
    Here is my TCM tune:
    17 Camaro Modified TCM Tune.hpt

    Went I pasted the shift times from a ZO6 directly into my tables it would start tieing up the shifts and you could feel it, i'm not sure if a clutch was coming on to fast or what but I'm sure that's probably what it was. There is just some other tables we don't have access to that need to be adjusted for the faster ZO6 times, or either there are actual mechanical differences in the 8L90 that make it shift faster in the corvette but I don't think that's the case.


    I drove it a good while, maybe 2 weeks and it never did get better, if I remember right I think it was only binding up on the WOT downshift to third, I think the other gears were acceptable, although they probably didn't feel as good as they are stock. But it was hard enough shift into third it would trigger traction control light on (i'm assuming because of the torque reversal, which makes you wonder how the whole drivetrain can be going 70+mph and completely stop or reverse direction and it not break something)

  17. #17
    Tuning Addict WS6FirebirdTA00's Avatar
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    Thanks for the info.

    Question on the RPM in the downshift table - is that the RPM before or after the downshift? Any idea?

    Take a look at a 2016 truck 8 speed tune. Some of their values were much lower than mine. Most of the areas I dropped a lot were higher RPM and low torque ratio. I may revisit based on your comments.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  18. #18
    I've wondered the exact same thing, my guess is that it could be a projected RPM based on calculated gear ratio and ring gear ratio, to control the reason why it short shifts on the 1-2 and the 2-1 downshift is limited. I guess because the transmission can't shift before it hits the rev limiter. I wouldn't think GM would program that based on the vss signal though so who knows?

  19. #19
    Tuning Addict WS6FirebirdTA00's Avatar
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    I only wondered if it was current RPM since there was a lot more definition at the bottom end. Projected RPM could be higher, but I don't see a case where projected RPM would be 1000 or anything low to need that kind of definition. That being said, it may need it for lower speed closed throttle downshift. Who knows.

    Still trying to figure out the torque ratio. The only thing that makes sense is the desired torque %.

    I am trying to go through with 20% reduction up top, leaving the high torque ratio areas within 10% and then the low RPM area down 10%. Then I just blend in between and try not to mess with the times closer to 0.300 or less.

    I assume the longer times on multiple gear downshifts give everything time to play catch-up (like RPM and line pressures). Then even longer at low torque ratio for the off or light throttle downshifts so it does not jerk. Just assumptions though. I went a bit faster and the downshifts coasting felt OK. I am less concerned about the upper right area as I am the lower and left area. I could be wrong, but the excessive times at low torque ratio and high RPM is nuts. Most areas are 1.2 seconds or longer.
    Sulski Performance Tuning
    2000 WS6 M6 - LS6 (long block, refreshed top end), 10.8:1 CR, 90 mm ported FAST, Exo-Skel, 227/232 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
    2018 Sierra SLT 5.3L A8 - Airaid intake tube, GM Borla catback, L86 Intake/Ported TB

  20. #20
    I can't find anything on EFI Live or HP Tuners supporting full OS flashing for the T87A with a quick search, but I think this is our ticket. We need to be able to full flash the ZO6 calibration that way we can get the ZO6 parameters flashed in that are hidden and not mapped in the 8L90 calibrations. I also can't find any mechanical differences between the corvette and camaro/truck 8L90 besides the obvious corvette one is a transaxle and slip yoke/non slip yoke.