Upshift Torque Reduction in LS1 Edit: what is it?
Does the PCM reduce timing during upshift?
Why? Is it a way to drive smoother or does it reduce the engine / transmission stress?
If it’s torque: how does the PCM knows how much timing will reduce so much torque?

I ask because I installed a Vortech tune: near other changes they put the Upshift Torque Reduction for 3rd and 4th gear to about 2%. The stock program reduces the torque of 30%.

Is it to increase the performance? Is this a typical setting if using a SC? Who else is messing with the Upshift Torque Reduction?

I know, maybe this is the wrong forum for my question: I’m asking about “tuning” a “transmission” for a “supercharged” engine… but I had to pick up a forum for this!

Thanks - Stefano

 

This is what most people refer to as TM (torque
management) although there are other aspects to
TM as well.

There are a couple of layers to it. First layer is the
upshift torque reduction vs torque by gear table. This
commands a percantage of torque to be pulled back.
Its only purpose is to let GM get away with a weaker
transmission than they should have put behind this
series of motors, for at least the duration of the factory
warranty. The torque index is the Delivered
Torque - Trans PID. This is a calculated PID that takes
the Delivered Torque - Engine (also a calculation) and
lays the (believed) torque converter multiplication on
top of that, based on slip and engine RPM. Of course
this is an utter hoax once you hang an aftermarket
converter on there, but anyway....

The second layer is a mapping of percent torque reduction
to actual spark retard applied. This is another prediction
and in my view it is quite bogus. The spark should pull
100 lb-ft, say, during a shift but your timing just slams
on down to -10 degrees. Thanks, Dad.

I have tried a bunch of TM fiddling trying to reach a good
compromise between trans protection and solid acceleration.
Where I have ended up is a reprofiling of the Upshift Torque
Reduction table (including adding TM to the 3-4, which is
naked from the factory), a reduction in the amount of
torque pulled in the spark retard vs torque reduction table,
and also setting the Max KR vs RPM (misnomer, it is actually
the "minimum spark advance under spark retard conditions"
table, or should be called that) to keep the TM from putting
spark underwater.

Upshot is, going this way means TM has limited authority,
it can cut torque only as far as 15 degrees WOT advance
lets it (which is still a substantial, but not total bang-your-
face-on-the-steering-wheel, torque cut).

As to why the supercharger people would mess TM around,
probably because nobody wants to spend all that dough
on a supercharger and still have the car die in the middle
of every shift. I would say just check their work, and maybe
apply a -little- bit of protection since the transmission's life
just got a lot more difficult.

 

Thanks, that was clear.
I'll probably go with the most conservative TM. My goal is not to beat the record but just to have a fast, reliable and long lasting daily drive. I was right happy with the stock transmission tune and now it really shifts too hard.
Maybe I'm getting old

Stefano

 

even though I know as much about tuning as I do about the composition of the moon....that had to be the most indepth, well thought-out and direct answer to any highly technical question I have seen on the forum. to jimmyblue.

Fry

 

True! Sometimes I'd like to have a "BS filter" when I look for serious informations in the forum (all forums!).

Jimmiblue is THE MAN!

Thanks again

Stefano

 

OK, Upshift Torque Reduction is back as stock.
Maybe the car is a little less wild now, but much more agreeable to drive!

Thanks again - Stefano