Shift Quality

[907DAVE]

What is the preferred method to firming or softening shift feel?

Is it by changing slip time, torque reduction, or TV pressure?

What are the negative affects of each?

I like the torque reduction feel for light driving, but dont like the "burn time" that comes along with it, what is best for my tranny?

[cleatus12r]

The easiest way to get a more firm but yet comfortable shift is to change the target slip time by reducing the values (it's time) by about .25-1 ms. The TV pressure is a baseline that gives the shifts a "head start" so to speak in the adaptive strategy. The PCM can compensate up to about 20 PSI in most cases to achieve the desired slip time. That's the easiest way.

Bill and I have differing thoughts on the torque reduction during the shifts. I won't get in on his side of the coin, but I prefer to use the stock reduction or even a little lower values in the low APP ranges simply because I think it's better for the transmission. Bill doesn't believe that's true and it may not be but he can explain to you his thinking on the deal and you can make a choice for yourself.


Negative effects? I can't give you any as a slightly quicker shift is always better for the friction elements inside the transmission. A "mule kick" in the seat during a shift is obviously not good. As long as you can get a quick shift, minimize burn time, and keep it comfortable, it's a good shift.

I can show you a couple of my shift parameters if you'd like to try them.

[907DAVE]

That would be awesome.

[cleatus12r]

Oh, and I forgot to mention that the OBS and E99 guys are SOL on the adaptive stuff.

I was kind of curious as to the TV pressure offsets and TV pressure slopes in the parameters menu. I tend to leave those alone but I assume they actually dictate the solid state line pressure in each gear. They do make the shifts harder when changed. I don't know though. I was actually trying to save that question for the tuning class......

But if you know, or Bill freely divulges the information, I won't argue with it.

[cleatus12r]

I will be right back. I'm busy making some screenshots...............

Give me about a half an hour.

[cleatus12r]

Ok here they are, in no particular order.............

Bill, I am not saying that these tunes are perfect so if there is something amiss, then please feel free to offer suggestions. These do work very well for me and the way I drive though.

[907DAVE]

Thanks Cody, gonna have to study and compare these. I did not know anything about the "torque table" but will have to look at that, and I was wondering what that was for.

[907DAVE]

I wasn't thinking straight about the torque reduction map. I had it in my head that it was part of the shifting strategy, when it was really just a map for how much power was "taken away" during a shift. I think I will have to agree with your way of looking at it Cody, if less power is being sent through the tranny while shifting, the less wear/stress there should be(at least I think that's what you meant). I would like to hear why you two disagree with each other on this.

Why not go beyond stock and increase the reduction even more for a heavy tow program?

(on edit, that exactly what it looks like you did)

I would assume the issue would be with keeping the turbo "lit" under heavy load and with such a great reduction it might be easy to get under the turbo, but the tranny would be pretty happy, but I am just assuming and we all know what that makes out of you and me.


Think I am going to have to start from scratch on this one.

Thanks Cody

[Power Hungry]

On the power reduction, many folks complain about the "dive" when the truck shifts and prefer to have the torque reduction removed. On some performance programs, we eliminate the torque reduction, but on tow programs we don't... for obvious reasons.

As for the Shift Slope and Offset, here's how it works:

The PCM calculates a specific amount of torque output based on the calculated torque table. Let's say this is 372 Ft./Lbs for a given Throttle Position and Exhaust Backpressure.

You multiply the torque by the slope for that particular gear to generate a Line Pressure PSI value. Using your towing (1st program) example above and assmuing 2nd gear...

372 * 0.1719 = 64 (63.9468) PSI

Then you add the offset...

64 PSI + 0 PSI = 64 PSI

64 PSI is what the PCM will set the EPC regulator to for main line pressure in that particular gear.

Make sense now?

[cleatus12r]

OH MAN does it ever make sense now!

Which is why adjusting the torque table map makes such a difference in pressure all by itself.

Thank you Bill.



I hope you had a good evening and that you and Corey as well as the kids have a great start to 2010!