Torque Truncation vs Torque Reduction

In the Torque Management tab under the Trans window of the 6R80 there are some switches for Torque Truncation and Torque Reduction. I know some tunes have these on, some off, some have the Torque Reduction tables maxed out with various switch states. I am wondering what happens when each individual thing is turned off: Torque Truncation, Torque Reduction Master Enabled, and Torque Reduction Shift Enabled.

The way I understand it is that turning the Torque Reduction switches off is the same as raising the Torque Reduction table values way up, but why is there a master enabled and shift enabled? Torque Truncation is a mystery to me, although I know in the engine torque management tab there are some tables that reference Torque Truncation and Trans Shift. So I assume there is some correlation there, just not quite sure what.

Attachment 53336

Thanks for any clarity on this.

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Im going to guess truncation is torque allowed into the transmission(engine torque) limiting. Torque reduction is torque allowed during a shift(y-axis is torque converter torque)(table populated with Out put shaft torque values).

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Originally Posted by murfie

Im going to guess truncation is torque allowed into the transmission(engine torque) limiting. Torque reduction is torque allowed during a shift(y-axis is torque converter torque)(table populated with Out put shaft torque values).

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by definition, truncation is to "cut short" so I think I agree with what you are saying, truncation is not even allowing the power to exist, where reduction is pulling back the power that already does exist.

The Torque Truncation works like the torque truncation controls in the MT82 Manual transmission. It is a torque value that if exceeded, the PCM will either close the throttle or run leaner AFR (near stoich at WOT) to limit torque output.

You can either raise the torque values to something like 1000 ft-lbs in the TCC truncation table or just disable the switch. Both will prevent the PCM from truncating torque.

The Torque Reduction switch, when disabled, will force the PCM to move forward with shifting into the commanded gear WITHOUT reducing torque by the values in the tables below.

This is not recommended for street use as it will likely reduce transmission life. Some people disable it for track use to reduce acceleration loss during a shift event.

It will shift much harder when disabled.

Yes, I left reduction enabled because it appears to just disable TM completely for shifts, which screwed up the GM transmissions so I knew better.

Still would like to know more about Rate Limiting though, I have it disabled.