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Commanded shift rpm's, car shifts earlier than set

This is a discussion on Commanded shift rpm's, car shifts earlier than set within the Computer & Tuning forums, part of the LSx Technical Help Section category; HPtuners tune. My car makes peak HP at 6700, so I'd like to have car shift at or near that ...

  1. #1
    TunedByFrost supporter rel3rd's Avatar
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    Question Commanded shift rpm's, car shifts earlier than set

    HPtuners tune.

    My car makes peak HP at 6700, so I'd like to have car shift at or near that same rpm. 2>3 shift is fine. The problem is, 1>2 shift happens sooner than commanded to.

    During a quick driving log the other day,
    With 1>2 shift commanded at 6800, it shifted at 6530rpm's
    With 2>3 shift commanded at 6600, it shifted real close to right on the money (maybe 6700)

    Why would 1>2 shift occur at 6530 rpm's if programmed to shift at 6800?
    I have MPH wot settings set 10-15mph lower than the actual speed it is shifting at, so I'm solely dependent on rpm's for shifts...or so I thought.

    How can I extend that 1>2 shift to 6700? Is there a setting I am overlooking?

    I guess as an option I could log another few 1>2 shifts and extend the MPH higher to try and force a later shift, but since it isn't hitting both the wot MPH and RPM now, it shouldn't be shifting, unless I am missing something?

    Unfortunately, I viewed the datalog to get my numbers, but forgot to save it.
    2002 Silverado Z71 ECSB HPTuners tuned by yours truly
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    Veteran 0rion's Avatar
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    both the rpm and mph flags have to be met before a shift will happen. It's always been my understanding that you don't want those 2 too far apart or it can cause it to hunt for shift points. This is from the old ls1edit days and it's been something I've just done ever since. I try to keep the mph close to what it should be and I've never had any issues.

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    TunedbyFrost.com Tuner Frost's Avatar
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    I had always heard what Orion had mentioned, but later reading seems to favor the MPH met THEN RPMs met to shift, and my playing around has shown the same. I have zero'd the MPH table before to test shifting by RPM and the car ran the same. I typically don't turn on autos quite as hard as m6s (depends on the setup really). But in any case, it's not unusual on an internally modded engine to have to really fudge the RPM number and log to get it where you want it. Tuned an AFR headed 402 recently and had to command 7375 to get shifts at 6700 from 1-2. The 2-3 seems to follow more closely to commanded for whatever reason. Remember also when we move commanded shift times to under a half second (I usually use .250) that adaption is disabled, so we don't have to worry about it learning over time and drifting around. Once you get it right, it will stay and continue to be repeatable.

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    Veteran 0rion's Avatar
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    Quote Originally Posted by Frost View Post
    I had always heard what Orion had mentioned, but later reading seems to favor the MPH met THEN RPMs met to shift, and my playing around has shown the same. I have zero'd the MPH table before to test shifting by RPM and the car ran the same. I typically don't turn on autos quite as hard as m6s (depends on the setup really). But in any case, it's not unusual on an internally modded engine to have to really fudge the RPM number and log to get it where you want it. Tuned an AFR headed 402 recently and had to command 7375 to get shifts at 6700 from 1-2. The 2-3 seems to follow more closely to commanded for whatever reason. Remember also when we move commanded shift times to under a half second (I usually use .250) that adaption is disabled, so we don't have to worry about it learning over time and drifting around. Once you get it right, it will stay and continue to be repeatable.
    I used to swear by that saying that you didn't want them to far apart but like you said, seems lately people aren't doing it that way and I don't really read about this problem that much. I just kept doing it the old way. I also keep my shift times at .250. I've also wondered how much convertor slip effects that 1-2 shift vs the 2-3 and 3-4. I noticed after my stall that I would bang the 1-2 limiter but not the 2-3 or 3-4. I kinda wondered if the rate of the rpm climb added to the short shift times is more prone to effect that 1-2 shift and let it slip past the shift point.

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by 0rion View Post
    I used to swear by that saying that you didn't want them to far apart but like you said, seems lately people aren't doing it that way and I don't really read about this problem that much. ...
    It could be different in some of the years as well. The one I mentioned with the MPH zero'd was an 01 with a stock 01 OS. Things back in the 98 PCM are so much different, it may be more important to get the MPH and RPM lined up, so I can't discount it. I usually tune to favor them lined up as well, always being careful to keep MPH beneath the RPM point since having the MPH set higher than the RPM can keep it from shifting at WOT.

  6. #6
    TunedByFrost supporter rel3rd's Avatar
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    FWIW, I finally got some full traction 1/4 mile datalogs today at a private track rental. For whatever reason, it seems the first few runs short-shifted themselves? I did make some corrections after scrutinizing the datalogs. Runs 4 through 20 were right where I commanded them to be, even though MPH settings are set artificially low.

    Yes, I said runs 4 through TWENTY, LMAO
    Last edited by rel3rd; 03-21-2008 at 08:03 PM.

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    Veteran 0rion's Avatar
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    was the car bogging at all maybe changing the load or was everything cold on those first runs? Probably not it but a possibility maybe?

    20 runs? Damn, your car hates you.

  8. #8
    TunedByFrost supporter rel3rd's Avatar
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    Quote Originally Posted by 0rion View Post
    was the car bogging at all maybe changing the load or was everything cold on those first runs? Probably not it but a possibility maybe?

    20 runs? Damn, your car hates you.
    No bogging. Car pulls the driver's side front wheel 2-3 inches every time.
    Car was surely cold the first run or two since I trailered it due to distance away from home, combined with stock rear.

    My car is deadly consistent.
    20 passes with ET's all within a tenth, MPH's within 1, Sixty foots within 3/100ths, and it didn't seem to matter whether I launched from IDLE, 1300rpm, 1500rpm or 2500rpm...or anywhere in between. It did spin hard on two passes when I tightened up adjustments on the rear shocks too much, but came right back in line when I re-adjusted them back to where they were. It also doesn't seem to make any difference whether I make four passes back to back, or let it cool down for an hour...Three different times I made 4 passes within minutes, round robin style.

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    TunedbyFrost.com Tuner Frost's Avatar
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    what ET and MPH? Awesome car, you should run some brackets Bob. Glad you got it figured out.

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    TunedByFrost supporter rel3rd's Avatar
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    Quote Originally Posted by Frost View Post
    what ET and MPH? Awesome car, you should run some brackets Bob. Glad you got it figured out.
    11.70@115 was best of the day.
    11.67@115 was best ever, but that was in 38* weather, and today was much warmer, so I can't complain.

    Sixty foots were pretty much all 1.60-1.61 with one 1.58 in the mix.

    Actually Frost, that is why I was trying to get this shift RPM thing dialed in...so I can race in the RAM Racing All Motor Index class. They have a 12.0 bracket and with some race day shift setting changes I should be able to dial in pretty quickly. I'm already quite sure she's more than capable of keeping up with all the round robin, back to back runs, hahaha...

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    TunedByFrost supporter rel3rd's Avatar
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    I posted up the info from all of my runs yesterday...damn my two fingers are hurtin...lol.

    Made a few passes @ MIR...lol.

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    The 1-2 shift happens so quickly that when you log the RPM's the actual shift RPM's are not real accurate-- even though your logger says that the shift is happening earlier--in reality it may be shfting exactly where you set it--To command a shift you must hit both the MPH and the RPM shift points--Make sure also that your shift at WOT MPH is commanded at least at a point that is 800 RPM less than the shift at RPM ponit--Example---If your WOT shift point is 6700--then set the MPH shift point when the RPM's are at 5900
    The more HP you have beyond stock--then the higher this split should be--On my 390 RWHP C5 --I have the split set at 1000

  13. #13
    TunedByFrost supporter rel3rd's Avatar
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    Here's a video from that day.



    The 1>2 shifts aren't happening all that quickly IMHO, but I understand what you are saying. I have my MPH settings for 1>2 and 2>3 shifts set much lower than 800rpm's, so that MPH has nothing to do with upshifts.

    I have HPtuners set at 6800 and 6750 respectively and according to datalogs, it shifts at 6770-ish and 6730-ish every time now.

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    It may not have anything to do with your particular problem--but at WOT you have to hit 2 parameters in order to command a shift--1st you must hit the MPH parameter and 2nd the RPM parameter--Most trucks and SUV's will shift with a 500 RPM split between them but a camaro or a corvette takes much more--usually around 800--

  15. #15
    TunedByFrost supporter rel3rd's Avatar
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    Evidently, you are reading right through what I have done.

    The "problem" I was having in original starting thread has been corrected. I wasn't able to get accurate datalogs on the street, due to traction. Once at the track with sticky tires and controlled WOT runs, I was able to datalog and adjust shift rpms only, which took care of issues.

    My MPH settings are set at 35mph for 1>2 and 69mph for 2>3 shifts

    According to datalogs, at WOT, at 35mph and at 69mph, I am at roughly 5500 rpm's, which is 1200-1300+ rpm's lower than my actual/commanded shift rpm's.

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    Sorry---I understand what you are saying now---THKS for clearing it up for me--

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    My God that car launches fast! Whatcha' got done? besides sticky tires

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    TunedByFrost supporter rel3rd's Avatar
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    Quote Originally Posted by TedsB4Csled View Post
    My God that car launches fast! Whatcha' got done? besides sticky tires
    "Baby" 226 cam and a 3600 PI Vigilante converter are the only things added to a basic bolt-on car w/longtubes. It weighs 3755# with me in it...

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