2016 8 spd auto

Transmission to Rear-end

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In-Tech
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2016 8 spd auto

Post by In-Tech » Wed Aug 22, 2018 1:05 am

Hello,
I thought I would post this for people interested in the newer transmissions as far as the control side. Back in the early 90's the 4L60e/4L80e were fairly easy to tune and adjust. It used to be I wouldn't charge extra to do a "tune up" to the trans parameters while doing the engine tune. Of course as newer controllers came out they had more "power/adjustability" so I had to add an extra charge if they wanted the trans tuned beyond a gear/tire change.

Now the 8spd stuff has almost the same size file(~4mb) as the direct injected engine file. :shock: My plan is to rent a uhaul pickup( :lol: ) and strap it to the dyno for a few days and attempt to figure out some things out so I can also figure out what to charge. :?

Anyways, enjoy. :wink:
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Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: 2016 8 spd auto

Post by Brian P » Wed Aug 22, 2018 12:32 pm

Yup. The newer transmissions are more efficient, but there's a lot more going on in there to make them work.

4 megabytes of memory is cheap. I'm surprised the configuration file is not more than that.

ZF builds lots of those transmissions but it's up to the auto manufacturer using them to set up the calibration, also, which means they're not going to all be the same between different manufacturers using what is nominally the same transmission. The Chrysler transmission is the ZF transmission built under license; it's similar but not exactly the same. The GM 8-speed is an entirely different unit.

That GM 8-speed may not be in production vehicles for all that long. The co-developed GM/Ford 10-speed should be replacing it.

The logic isn't like what it was in the old days, either. It's more than just higher road speed influencing the transmission to upshift and more throttle influencing it to downshift. My (Chrysler) van downshifts when going down a steep hill, even at zero requested throttle, to give engine braking (whether you want it or not - there are times when I wish I could disable this). After slowing down with shut throttle it picks various combinations of which gear to engage and torque converter locked or unlocked depending on what speed you get back on the throttle and how quickly you press the accelerator. It all works, it seldom feels like it was caught in the wrong gear ... and this is the hoary old 6-speed automatic. But that's gotta be complicated.

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Re: 2016 8 spd auto

Post by In-Tech » Wed Aug 22, 2018 1:57 pm

Brian P wrote:
Wed Aug 22, 2018 12:32 pm
4 megabytes of memory is cheap. I'm surprised the configuration file is not more than that.
It's quite large if you have to disassemble and trace :lol: The 1991-1993 454 4L80E file was only 256K and that was the engine AND trans. :wink:

I agree, the new decel stuff is pretty cool.
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: 2016 8 spd auto

Post by Brian P » Wed Aug 22, 2018 2:47 pm

Oh, no doubt. What's in that memory was probably also created using a compiler from a higher-level language, which adds a bunch of bloat, which for your purposes doesn't do anything but still has to be traced if you have to figure out how it works. No one cares about how much memory something uses any more. It's too cheap to worry about.

I just checked the file size of a quotation that I just wrote up for a client. No photos or anything fancy. It's a two-page document. It's 305K.

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Re: 2016 8 spd auto

Post by peejay » Thu Aug 23, 2018 7:14 pm

Brian P wrote:
Wed Aug 22, 2018 12:32 pm
4 megabytes of memory is cheap. I'm surprised the configuration file is not more than that.
The implication is that there is a lot of processing power required to process all of the different tables and maps that would require 4 megs.

I know on some older generation stuff (not GM) there were six or seven different MODES with their own shift strategies. If you were attentive you could notice the trans going from one mode to the next, and learn to exploit it. Like if you knew that hitting the accelerator rapidly would trigger a shift to a mode that would hold the trans in gear longer without upshifting, you could stab the throttle a couple times while entering a corner so that it wouldn't upshift in the middle of it. As an example that I used to exploit all the time.

Another thing that works a lot of times for better fuel economy is to turn cruise control on. You don't need to be USING it. Merely having it on will put the engine and transmission controllers into a different mode that usually gets better economy.
Last edited by peejay on Thu Aug 23, 2018 7:17 pm, edited 1 time in total.

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Re: 2016 8 spd auto

Post by peejay » Thu Aug 23, 2018 7:16 pm

Brian P wrote:
Wed Aug 22, 2018 2:47 pm
Oh, no doubt. What's in that memory was probably also created using a compiler from a higher-level language, which adds a bunch of bloat, which for your purposes doesn't do anything but still has to be traced if you have to figure out how it works. No one cares about how much memory something uses any more. It's too cheap to worry about.

I just checked the file size of a quotation that I just wrote up for a client. No photos or anything fancy. It's a two-page document. It's 305K.
As someone who got online in the 1990s when a lot of services still charged per-megabyte, that just plain HURTS!

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Re: 2016 8 spd auto

Post by Brian P » Thu Aug 23, 2018 10:45 pm

Yeah I've had to squeeze programs down to the bare minimum, first so that they would fit within 32K of memory, second so that they would not take a million years to complete. Those days are gone.

On attentive drivers exploiting shift strategies ... I do that, too. With the Chrysler van, the thing to do is to have the trip computer set to display instantaneous fuel consumption. Normally when you coast down a hill, it will do the auto-downshift thing to avoid speeding up. If you WANT to use the downhill to speed up, keep your foot on the accelerator just a bit so that the fuel consumption display shows just above minimum (it won't display below 2.0 litres per 100 km), then the computer realizes that you want to speed up and it stays in the higher gear and lets the van accelerate. And, when coming up to a stop, when it drops through 70 km/h while coasting, it does an auto-downshift to 5th gear to give the driver some engine braking. If you don't want that, you feather the accelerator pedal just a smidge while it's dropping through 70 km/h, and it will stay in 6th and let you coast longer.

Cruise control ... the route to the race track that I usually go to (bike in tow, van full of stuff) has lots of rural secondary roads, and the objective for mileage is to keep it in 6th with the torque converter locked. There's a few hills where I know just how many "accel" taps are needed going down the hill followed by "decel" taps going up the next hill so that it stays in that gear. The fuel consumption display is the trick ... when it starts getting near 15 L/100 km in 6th, it's nearing full load and will want a downshift; the right sequence of "decel" taps keeps it just below that threshold.

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Re: 2016 8 spd auto

Post by bigblockmopar » Fri Aug 24, 2018 4:14 pm

Interesting stuff. Thanks for sharing that report.

Looking in the file and some of the first tables, I'm wondering how the Torque-value is "measured"/known to base shift-points on?

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Re: 2016 8 spd auto

Post by peejay » Fri Aug 24, 2018 7:21 pm

Engine controllers are often/usually torque based now. The accelerator pedal is the "torque demand" input. The engine's torque output is a known factor.

In GM controllers from 20 years ago, they had tables for engine friction torque vs. calculated oil temperature, engine torque vs. A/C system high side pressure, etc. That's for little 512k controllers running relatively crude drive by wire, with no variable cam timing involved.

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Re: 2016 8 spd auto

Post by In-Tech » Sat Aug 25, 2018 5:27 am

peejay wrote:
Thu Aug 23, 2018 7:16 pm
Brian P wrote:
Wed Aug 22, 2018 2:47 pm
I just checked the file size of a quotation that I just wrote up for a client. No photos or anything fancy. It's a two-page document. It's 305K.
As someone who got online in the 1990s when a lot of services still charged per-megabyte, that just plain HURTS!
Yeah, 305k for a 2 page document with no pics? What kind of editor are you using? :shock:

Shoot, even that calibration file(no code, just lookup values and tables) I posted is only 171K(folks, remember to turn word wrap off if using a "cheap editor" like notepad, so the larger tables don't get all garbled) and it's still roughly 85 pages long depending on your screen size. :wink:

Anyway, I'm glad some of you took notice. There is a lot going on in the new stuff and truly I am not looking forward to messing with it. Shoot, if it's anything like what happened with the 6 speed stuff, there will be new updates all the time. There has always been good stuff to learn when a new update comes to solve issues that customers have complained about. Comparing can be a daunting task, it does aid in the learning process though.

I'll admit it, there have been times where I have just thrown in the latest update and my customer will call back and tell me WOW, I don't know what you just did 'lil kid but that transmission works soooo much better. :mrgreen:
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: 2016 8 spd auto

Post by Brian P » Sat Sep 01, 2018 8:12 pm

Compare the normal upshift speed to the TCC apply speed.

Let's pick moderate acceleration at 25% throttle in the "normal" tables.

The torque converter doesn't lock in 1st gear. That's typical. (Driveability)
At 9.0 mph it upshifts to 2nd.
At 10.3 mph TCC lockup. It's left unlocked just enough to cushion the shift.
At 16.2 mph upshift to 3rd. Presumably this also momentarily releases TCC lockup.
At 16.8 mph TCC lockup. Again, just enough to cushion the shift.
At 24.9 mph upshift to 4th. This happens beyond the TCC lockup speed in 4th, so it stays locked. Same is true for all following upshifts - they're all beyond the TCC lockup speed so the torque converter stays locked through the shift.

Spot checking other throttle positions suggests a similar pattern although obviously at different speeds. Same sequence.

This is a far cry from the old days where it only locked above a certain road speed (40 - 45 mph or so), or only in top gear and only at light load ...

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Re: 2016 8 spd auto

Post by In-Tech » Wed Sep 05, 2018 10:46 pm

Hi Brian,
Here is a calibration details file for a 2010 Vette 6 speed auto, if you don't have one already. I never liked how the trans shifted but still never touched the trans program over the years when doing engine tuning for Fast intake, 102mm TB, long tubes, etc. We just installed a supercharger and it was doing some funky stuff on the dyno and on the street, even more than usual. I am going to get the latest trans update and see how it acts. Hard to believe it has a 6 speed AND 2.56:1 rear gears. Lot's and lot's of crap going on in the trans when driving around town.

Owner has never complained about the constant shifting lock/unlock thing but I think it might be time for me to play with the program a little. :wink:
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Re: 2016 8 spd auto

Post by MadBill » Fri Sep 07, 2018 12:50 am

The 6 speed in my 2014 Impala was truly terrible when new. Clunky, ill-timed shifts, dithering uncertainty, etc. Fortunately I procrastinated on getting it repaired long enough to realize it was steadily improving, but it took probably 1,000 miles to complete its learning curve. Started out as a 4 and wound up as a 8.5* out of 10. #-o *What I dislike most is the "calibrated by lawyers" first/reverse shift delay, presumably to protect the tranny at the expense of not being able to rock your way out of a snowdrift. "Hey, it saves on warranty and besides, that's what AAA is for!"

Not the best situation for selling the customer via a test drive in a zero mile demo...
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Re: 2016 8 spd auto

Post by In-Tech » Fri Sep 07, 2018 4:06 am

Yeah Bill, the delays and the torque management stuff can be pretty crazy in this newer stuff. The adaptive learning works quite well but can be a bit slow in the early stuff. This is where an update really shines, the less it has to "adapt" the better.
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl

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