Beginner G8 GT trans tuning

[bluessv]

I'm wondering if your "Base Power Downshift" time of 0.2002 is too low when you take into account the "Shift Time Inertia Adder" for that particular downshift.

You'll notice the majority of the Downshift (Normal) tables in the Inertia Adder add to the Base Time (0.2002) or at worst they are zeroed out. Except the 6-5 downshift actually has all negative figured thus taking even more time off your 0.2002 Base Time. As a result, you may be asking too quick a shift time for that particular shift only.

Perhaps try adjusting the "Base Power Downshift" time for the 6-5 shift back to stock and see how that feels. If there is no difference at least you've ruled out that your asking to quick a shift.

[SoCal]

Good find, bluessv.

Allmachtige, you may have already noticed this. The stock 2009.5 tune has Tip-In CT Downshift set to NONE. It would be hard to believe GM would leave in anything that was too abrupt feeling. (exception to the rule : the stock tune trying to throw you onto the dash at heavy throttle shifts when TQM completely neuters the engine. ) They made a bunch of other changes, too. So maybe one of those lets them get away with NONE. I don't see an obvious answer. "Inertia Factor Profile : Power Downshift : 6-5" doesn't sound like it should be related. But it is drastically different from 2009. I don't understand what "Axis Xref" means. If you are operating in the 0.800 or 0.900 rows, the numbers are much smaller. I think that means things would feel softer. ???

[Allmachtige]

I'm wondering if your "Base Power Downshift" time of 0.2002 is too low when you take into account the "Shift Time Inertia Adder" for that particular downshift.

You'll notice the majority of the Downshift (Normal) tables in the Inertia Adder add to the Base Time (0.2002) or at worst they are zeroed out. Except the 6-5 downshift actually has all negative figured thus taking even more time off your 0.2002 Base Time. As a result, you may be asking too quick a shift time for that particular shift only.

Perhaps try adjusting the "Base Power Downshift" time for the 6-5 shift back to stock and see how that feels. If there is no difference at least you've ruled out that your asking to quick a shift.

Ahhh good find!

I'm going to try zeroing out the 6-5 Shift Time Inertia Adder table because this feeling is not under "power" downshift conditions, just normal driving.

I'll let you know.

[bluessv]

The TCM has a number of downshift tables to work with (CT, Min Power, Power). Does anyone know what driving conditions determine when the TCM will use Min Power table instead of Power?

I'm guessing the TCM doesn't use the Power Downshift table only when at WOT because if you're cruising in 6th and tromp it the box doesn't make a 6-5 shift....it usually makes a 6-4 or 6-3....and if you're lucky in Sports mode a 6-2!!!

Anyway...so does anyone know when the various tables are used??

[LSX378]

The TCM has a number of downshift tables to work with (CT, Min Power, Power). Does anyone know what driving conditions determine when the TCM will use Min Power table instead of Power?

I'm guessing the TCM doesn't use the Power Downshift table only when at WOT because if you're cruising in 6th and tromp it the box doesn't make a 6-5 shift....it usually makes a 6-4 or 6-3....and if you're lucky in Sports mode a 6-2!!!

Anyway...so does anyone know when the various tables are used??

Some great work here guys!

Chris etc may chime in on this, but it is likely that the TCM interpolates between "base" and "min" on power downshift, dependant on torque and/or throttle position between closed and the WOT entry/exit point. Though of course could be incorrect on that .

[Allmachtige]

The TCM has a number of downshift tables to work with (CT, Min Power, Power). Does anyone know what driving conditions determine when the TCM will use Min Power table instead of Power?

I'm guessing the TCM doesn't use the Power Downshift table only when at WOT because if you're cruising in 6th and tromp it the box doesn't make a 6-5 shift....it usually makes a 6-4 or 6-3....and if you're lucky in Sports mode a 6-2!!!

Anyway...so does anyone know when the various tables are used??

Good points. I was thinking about this today.

I basically just use your TCM settings in Sport mode but never really questioned why you raised the Min Power Downshift table to .2002 from .14xx.

Er, at least I think its your tune.

[bluessv]

Yeah...it's not my tune cause I've never played around with the Min Power Downshift tables. I learned recently thought that most of the time when the base table (Min Power Downshift) is increased to 0.2002 it's because other tables that also apply to the shift that usually add to the shift time have been zeroed out, eg. the Inertia Adderand Torque Adder tables. When this happens the stock time of 0.1492 is too quick for the trans.

That's what led me to look at the times logged in the Inertia Adder tables for the 6-5 shift and found that they were in fact negative numbers and were therefore taking time off the base reference tables. And that's why I thought you may have been getting a harsh shift because, unaware to you, you were making the shift time too quick.

I found with a lot of the downshifts, the Torque Factor Adder tables play a big part in the shift time. Unlike the upshift Torque Adder tables which don't add much, if anything, to the shift time unless you're very low revs/torque.

[Allmachtige]

I'll need to look deeper into my tune because I don't recall zeroing out much of anything, so I think I could bump my Min Power Downshift back down to .1492.

Those negative numbers in the 6-5 shift were stock.

[Allmachtige]

I looked everywhere and can't see anything else that would prevent me from setting my Min Power Downshift to .1492.

Also what Torque Factor Adders are you referring to? I thought that was only for upshift TQM in the TQM tab.

[bluessv]

I believe your issue may be that the harsh feeling your getting is when the TCM is actually commanding a "Base Power Downshift" as it is this table which has been significantly reduced from stock.

I don't think it when the TCM is using the "Min Power Downshift" table as I agree with what you're saying in reference to the zeroing out of tables. Perhaps just try the "Base Power Downshift" table for the 6-5 shift as stock and see if you get a noticable difference??

The Torque Factor Adder tables I'm refering to are the one directly under the Upshift Torque Adder tables. These too add time to the overall shift, but my original suggestion referred to the Inertia Factor Adder table for the 6-5 downshift which has all negative figures. As a result, if you change the "Base Power Downshift" from 0.2998 (stock) to 0.2002 it might be just enough to be asking too much when you consider the negative figures?? Just a suggestion, not a gaurentee fix.....yet??

[bluessv]

By the way........

This afternoon, for the first time, I "zeroed" out all the "Desired Output Torque" tables and gave it a run. These tables are right down the bottom left hand side of the "Shift Properties" tab and have tables relating to upshift Normal, Special and Downshift.

I first read about these tables from the good guys at the Tuning School but never played with them as I didn't really understand them. I took a punt and "zeroed" them out as recommended and the improvement was out of sight....especially for the 1-2 and 2-3 upshifts.

I'm the type of guy that likes tunes with more TM than the average guy on this forum and I'm also a fan of "Discrete Shift Torque".....all of which are personal preferences.

The "Desired Output Torque" tables are used to control shift feel, along with other segments of the tune, and allow GM to make the shift feel the way they want it to. Again, info from the Tuning School.

If there are any guys out there that are still runing tunes which haven't touch these tables from stock, then I recommend you "zero" all the "Desired Output Torque" tables relating to Normal, Special and Downshift. I believe it feels great so hopefully you'll love the shift feel too.

AND REMEMBER....DON'T TOUCH THE MULTIPLIER TABLES DIRECTLY NEXT TO THE RELEVANT SHIFTS.....LEAVE THEM ALL AS STOCK WHICH SHOULD BE "1"

Let me know what you think if anyone makes these changes

[8850]

How are your shifts with the tables zeroed out? Softer or more firm? Are you indicating WOT shifts or part throttle?

My 1-2 special has multiples of zero and one factory settings. Should these be changed to 1?

[bluessv]

I was talking about part throttle shifts and the shifts feel more firm. But only slightly. For the most part it appears to take away that "slushy" feeling that the 6L80 is famous for when it is calibrated anywhere near stock.

I have been advised to leave all the "Multi" tables alone. What ever they are as stock, usually "1", just leave it. The tables just to the left of those which are applicable to specific shifts (Normal, Special and Downshift) should all be "zeroed". Some of the tables will already be "zeroed" from stock but there are several tables, mainly relating to 1-2, 2-3, 3-4 and 4-5 upshifts that have calibrations in them. They are the ones that should be "zeroed".

Of course it's a matter of trial and error, and personal preference too.

I haven't confirmed this yet, but it may not have as a big an impact with those of you who are running tunes with most of the stock TM removed. Just a theory though?

[04blackgmc]

ive really been debating on dropping the desired output torque tables to 0 alone with
shift time torque adder/shift time interia adder

and bumping the main tables up to .25 and seeing how it is but really havent got around with testing it.

i remember the tuning school saying to do this.

[Allmachtige]

ive really been debating on dropping the desired output torque tables to 0 alone with
shift time torque adder/shift time interia adder

and bumping the main tables up to .25 and seeing how it is but really havent got around with testing it.

i remember the tuning school saying to do this.

I did all this from the tuning guide awhile ago and hated it. It felt like I was driving a racecar on the street. I was pretty much getting looks from drivers in my car watching the front end lurch like a seizuring child.

I went back to your tune (shane's) with your slightly lowered Torque Adder, Shift Time Transition, etc etc tables.

I might try just zeroing out the Output Torque tables, but might bump the other tables back up to stock.

I've always wanted to ask you shane...why did you chose the numbers you did for Shift Time Transition, Shift Time Input Torque Adder, and what have you?

[04blackgmc]

I did all this from the tuning guide awhile ago and hated it. It felt like I was driving a racecar on the street. I was pretty much getting looks from drivers in my car watching the front end lurch like a seizuring child.

I went back to your tune (shane's) with your slightly lowered Torque Adder, Shift Time Transition, etc etc tables.

I might try just zeroing out the Output Torque tables, but might bump the other tables back up to stock.

I've always wanted to ask you shane...why did you chose the numbers you did for Shift Time Transition, Shift Time Input Torque Adder, and what have you?

When I get home I'll explain some of it but I'm typing from my iPod right now heh

[04blackgmc]

Ok...
with the inertia adder normal and special just worked off some percents and worked it where it looked good.

the torque adder tables worked 5% down not alot.

and the shift time transition tables worked off percents.

[Allmachtige]

Ok...
with the inertia adder normal and special just worked off some percents and worked it where it looked good.

the torque adder tables worked 5% down not alot.

and the shift time transition tables worked off percents.

I appreciate the homework you put into this.

Have you tried zero'ing out the Desired Output Torque tables with these settings?

[LSX378]

Nice looking rides those G8's! Do you get many looks in the traffic considering they are probably reasonably rare?

[04blackgmc]

Ok did some testing with some new stuff tonight trying to make normal very very close to stock and sport way different

Worked great!

Small problem though everyone once in awhile after a new flash when doing a dig or 1st gear punch the car has a weird feel let's say around 4k the car kinda drops off for a split second and then kicks back in(I know other people have had to experience this)

well I did do a pretty new calibration it did it a few times then threw the cel.

Codes were p0700 and p0716 the 700 just means the tranny comanded the cel. Now the 716 has to do with the speed sensor not matching up.

So I think it just freaked out like I said it has happened before but never threw the cel.

Did a few more digs after that no problems