Guide to Shift Scheduling - Part 2

[breal5825]

In my last thread, I got where I needed to be to log all the parameters so I could attempt to do my own shift scheduling. Here's what I've discovered. In regular, everyday driving, the Shift ID that my car is in 95% of the time is Shift ID 5. When I go into the VCM Editor, does that mean that if I want to modify the shifting pattern, I need to go into Transmission Shift Pattern 5?

Basically what's happening is, I have a Stage 1 package on my 392. There's a lot of stuff tacked on to the car now but at its core, it's ported heads and a cam. The engine is now making 600hp. While driving down city streets at less than 60mph in standard driving mode (not Sport Mode), the car is trying to shift up too high. You know how if you shift a manual transmission up to high and you're going to slow, the car jerks a bit but once you downshift you're rpms pickup but now the car is smooth? That's what I want to achieve.

In short, I'd like to modify the shift pattern so that when I'm slowing down or just gliding along at like 10% throttle, anytime the car hits 1,250 rpms, downshift. If I have 0% throttle and/or I'm applying the break, I'm OK letting it drop to like 1,100 rpms before it downshifts, like it's basically doing now. Am I on the right track?

[spoolboy]

If the shift ID is 5, you're using table 5. That would be the one to modify. Be aware that there is probably a different table for "spontaneous downshift" around 81(?) or so and your shift table may move around based on agression or which drive mode you're in (sport, eco, etc)

[breal5825]

And... adding on to the original post, if indeed VCM Scanner Shift ID 5 = Transmission Shift Pattern 5 in the VCM Editor, could I just raise all the downshift values by like 125rpm? Honestly, if the car would downshift 125rpms sooner everytime, that would be exactly where I want to be. Thoughts?

[breal5825]

If the shift ID is 5, you're using table 5. That would be the one to modify. Be aware that there is probably a different table for "spontaneous downshift" around 81(?) or so and your shift table may move around based on agression or which drive mode you're in (sport, eco, etc)

And I'm OK with that. When I really have my foot into it and/or I'm in Sport Mode, the thing shifts exactly how I want it to. The only time I want it to downshift sooner is in regular driving mode while moseying around city streets at like 10%. Ya know, those times when you're in traffic and you can't really get on it. The last log I took had Shift ID at 5 almost exclusively when I was doing my test drive. OK so, maybe my theory of raising all the downshift values up by like 125 rpms is the way to go. Would anyone see any danger in that?

[spoolboy]

The upshifts and downshifts are sort-of inter-related, in that they overlap.
You won't hurt anything by trying what you're asking, but be aware that those tables are in output shaft RPM not engine rpm. 125rpm is not the same in each gear.

It's possible you'll have a histeresis problem where the trans shuffles between 2 gears if you only change part of the map. But probably not.

[breal5825]

The upshifts and downshifts are sort-of inter-related, in that they overlap.
You won't hurt anything by trying what you're asking, but be aware that those tables are in output shaft RPM not engine rpm. 125rpm is not the same in each gear.

It's possible you'll have a histeresis problem where the trans shuffles between 2 gears if you only change part of the map. But probably not.

Oh!! It's output shaft RPM... Duh. I was trying to understand why the values are so low, like for 9.8% throttle, the 1->2 shift point is 255. I'm like, the car is NEVER at 255 rpms. It would have stalled long before it reached that point. Now this chart makes sense.

So knowing that 6th gear is the 1:1 gear ratio in the 8HP70 transmission, when I look at the 9.8% throttle row, I see the 6->5 shift point is 900. If I want my car to downshift at 1,250 rpms, I need to increase that shift point by 1.3888889% to get to 1,250 rpms. I say that percentage because that's the amount I would need to increase all values by on that table to get my desired behavior. Sound like pretty solid logic? Am I missing anything?

The only values I might leave alone on this table would be the values at 50% throttle or higher because if I have the throttle down that hard or harder, the table is fine just the way it is. This increase I would only want to apply to the car at low speeds.

[spoolboy]

Here's an excel spreadsheet. You can change the data in orange areas and it will output in the white areas.

Then you can copy/paste into the shift schedules.

You have to allow more rpm "lead time" in lower gears for the trans to complete the shift.

oss.xlsx

[breal5825]

Here's an excel spreadsheet. You can change the data in orange areas and it will output in the white areas.

Then you can copy/paste into the shift schedules.

You have to allow more rpm "lead time" in lower gears for the trans to complete the shift.

oss.xlsx

Shift Tables Spreadsheet.xlsx
Spoolboy, my good sir... This spreadsheet has been an absolute God send. I've added a few rows and columns so I could visualize the separation between the output shaft speed on upshift and downshift so I wouldn't get into a situation where the car upshifts but, by the numbers, it should immediately downshift. That would be bad, obviously. By having the gear ratios figured into everything, I could enter in desired downshift RPMs and then enter when I would need the upshift to go, how many RPMs I would lose or gain depending on which way I was going, etc.

Also, your initial spreadsheet was missing the formulas in cells Z3 to AF14 but I was able to follow what was happening and I added them back in. Check out this spreadsheet I've created based on your original spreadsheet. I copied in the default table #5 and table #6 for reference and placed them on separate tabs. I also have a proposed table #5 tab added. This is the table I'm thinking of uploading into my PCM.

I've boxed in the changes I've made. As you can see, it's a little more aggressive in the lower gears but smooths out and in the upper bands, matches the default table #5 exactly and that's what I'm looking for. I want it to shift a little later at low speeds and downshift sooner when slowing down at low speeds. I think this will accomplish what I'm looking to do. Plus, if I have to get on it, it'll behave as it always has when driving in regular mode and if I ever want to get aggressive, like on the highway, I'll put it into Sport Mode.

Really appreciate your time with this and hey, do you do this for a living or are you a hobbyist like me?

[spoolboy]

Looks like you've got the right idea. You'll just have to try it and see how it works for you.

If you are not familiar with them, you may want to try the interpolate and smoothing functions.

[breal5825]

Looks like you've got the right idea. You'll just have to try it and see how it works for you.

If you are not familiar with them, you may want to try the interpolate and smoothing functions.

That's actually what I used to get to this point. I did the first two rows, upshift and downshift at and below 9.8% throttle, manually and then plugged those into the table in VCM Editor and smoothed out the columns from top to bottom for each row. I guess at this point I just have to bite the bullet and upload it into my PCM. I'm just worried to all hell that I missed something somewhere and there's going to be a situation I didn't anticipate and I'll end up damaging my car somehow. Between buying this car brand new in 2016 and then tacking the Stage 1 package on to it this past summer, I've put a lot of money into my baby and would be beside myself if I loaded this table and it somehow damages the transmission.

Is that even possible? I just wish I knew the risk of what's the worst that could happen. I will be saving a copy of the default table on my laptop so I can always go back to factory but again, if I damage something, that's not going to do me any good.

[spoolboy]

When you modify a car, anything can happen. These are risks you must accept when you choose to modify one.

That being said, compared to what you've already changed on the car, this is pretty low-risk.

[breal5825]

When you modify a car, anything can happen. These are risks you must accept when you choose to modify one.

That being said, compared to what you've already changed on the car, this is pretty low-risk.

OK. That's what I was thinking too. The worst thing that could happen is the car shifts back and forth between gears too frequently and I need to make some adjustments. Well, no guts no glory I suppose. I'm going to load that spreadsheet into my PCM and see if it starts shifting how I want it to. I'll post up with the results as soon as I have them.

[breal5825]

So shift tables have finally been loaded and the first test drive is done. I'm stupid happy with it. Log file is attached but yeah, I love the way it drives now, especially when slowing down, it's downshift so much sooner and that's awesome.

Brandon Test Drive, Standard Mode, New Shift Tables, 2019-11-01.hpl