Torque Management based on calculated values in PCM needs "tuning"
This is just a quick note to alert Fanatics to an important potential shortcoming in the "torque management" fearure on our SSRs.
The torque management feature is a PCM function that reduces engine torque (and therefore power) during gear shifts, via spark retard and electronic throttle override, whenever the PCM "calculates" instananeously that the torque being produced exceeds certain conservative limits programmed in BY GM to protect the transmission and rear axle assembly.
There is also an unsubstantiated rumor that GM adjusted torque management to ratehr conservative levels on 05 SSRs, via a quiet reflash during other mechanical service, when it determined that its warranty experiences were a little too costly.
At any rate, the key point of this posting is that the PCM uses a CALCULATED value to estimate instantaneous engine torque output, which it calculates based on sensor inputs (air flow, manifold vacuum, etc).
In the course of the electronic logging and tuning that Lyndon Wester and I are doing in slowly and carefully tuning my newly installed supercharger setup, I am seeing lots of internal PCM data that I had never needed to pay attention to before. One of the fields I am seeing is this calculated power field. (Torque is simply = Power x 5252 / rpm, and that's how the PCM "calculates" torque from the sensor derived power number)
What has struck me is the obvious INcorrectness of that calculated power value. During datalogging, I am seeing values in excess of 800 hp!! This tells me that the alogorithm used to calculate this "power" value is either flawed or extremely conservative to protect the powertrain.
The significance is this: on a stock 03 / 04 SSR, torque management ("torque reduction" in GM speak) kicks in with a 7% reduction when calculated engine torque hits 280 ft lb, ad peaks at 40% reduction at a calculated 640 ft. lb., the highest torque value the PCM will recognize.
Now, stock SSRs do not make 640 ft lb even at peak engine torque, in REALITY, so would never hit that 40% reducton. BUT since the PCM calculates apparently wildly high torque values via its algorithms (I have seen over 800 ft lb in person in this value), it would seem that the PCM IS reducing torque during shifts beyond even what was intended.
I am filing this info away until I have to time to research and analyze it further, but there appears to be reason to do that analysis. IF I am correct (I might not be!), that would suggest that some "tuning" of the torwue management is a good idea.
Again, I would advise, as I have in the past many times already, against diabling the torque management altogether, as I suspect that that could be pretty hard on the drivetrain.
doesn't it reduce the torque at the shift point.....soooooo when the shift is made, torque mgmt comes in....and with the new converter you have installed, it might drive this number even higher because it can "shock" the system even more and drive the torque reduction the PCM calculates it needs even more.
The PCM is "unaware" that I have a high stall converter installed. We did not change any programming to accommodate the new converter.
Furthermore, there is only torque multiplication when (a) the engine speed exceeds the rpm required to match road speed AND (b) the engine rpm is BELOW 3000 rpm. Neither of these conditions is met during an upshift.
I have been told that the 6 speed also has torque management. I should have my HP Tuner software anyday, then I will be able to say yes or no for sure.
__________________ http://www.leftcoast32.com
'07 Black TrailBlazer SS "MP122HH" MagnaCharger
'05 SSR 6 Speed 427 "MP122HH" MagnaCharger Authorized MagnaCharger Dealer/Distributor
My SSR: Silver '05 6-speed, 4.10 gears, Flowmaster, Lakester Wheels, Ground Force springs
Quote:
Originally Posted by 2005SSR6Speed
I have been told that the 6 speed also has torque management. I should have my HP Tuner software anyday, then I will be able to say yes or no for sure.
Joe - yes it does. Very easy to remove. In HPtuners go into
Engine - Torque Management - ETC Limits, ECT TPS MAX - change all values to 100
Then go into Spark Retard VS Torque Reduction and change all values to 0
This will remove all TM in the 6 speed. The same changes can be done to the Auto - BUT - it will also disable the Traction Control. SO do not do it in the auto unless you know what can/will happen if you screw up. This is on the 05/06 - not sure how the 03/04 works.
Ross - Thanks, I hope my software gets here real soon, I ordered it after we last spoke. Keith said it would ship this week. We need to get together some time real soon so I can see how nice your SSR is doing.
__________________ http://www.leftcoast32.com
'07 Black TrailBlazer SS "MP122HH" MagnaCharger
'05 SSR 6 Speed 427 "MP122HH" MagnaCharger Authorized MagnaCharger Dealer/Distributor
Jim - Yes, on the 05/06 it does. The light will still come on but, the first time I found a "wet spot" it would smoke the tires. The tables that i changed are the end tables that control the total TM & TC that are allowed in the ls2. Ross
If true, and if I am understanding correctly, this was an ill-advised change in the way the PCM software functions, with safety implications.
Once 11.5 inch wide tires on a 5000 lb. rolling package let go, it is extermely difficult for a human to react quickly enough to prevent sustained movement off the intended direction of travel.
On the more sophisticated Corvette system, it is possible to disable traction control but still maintain electronic stability control.
This unwise software quirk (disabling of traction control automatically along with torque control) may be the result of the initially unplanned transplant of the LS2 powertrain from the Corvette into the SSR, without also transplanting the electronic stability system. I'm surprised that this got by the GM safety people, if as described.
what you are saying is that torque multiplication only takes place at the launch and not through some or most of the power band, and never at shift points?
Yes, The way a torque converter works is pretty straightforward:
A torque converter is (oversimplifying) two metal fans facing each other. One is connected to the crankshaft of the engine, and the other to the transmission input shaft. The converter can only multiply torque when the "engine fan" can turn at higher rpm than the "transmission fan". It does this by converting the extra rpm at engine torque into slower rpm at higher torque.
It's sort of like the gearbox: if you will accept slower output rpm than input rpm, you get more torque. That's why you have 1st gear to accelerate, and 4th gear to cruise.
Another way of looking at it is this:
Torque =force applied in a circular path at a specified radius
and
Horsepower = Torque x rpm / 5252
(that's a well known formula you can re-derive if you like mathematics )
The engine torque fed into the converter is at engine rpm, so
torque being transmitted = Force x radius
and Power = Force x radius x engine rpm / 5252
If you "convert" this by making the engine-driven fan drive the transmssion fan at say half the engine rpm, then since energy (power) is conserved, your equation becomes:
Power into tranny = NewForce x radius x half engine rpm / 5252
Since power has not changed between the two scenarios:
Force x radius x engine rpm / 5252 = NewForce x radius x half engine rpm / 5252
or
Force = NewForce x half
or
NewForce = Force x 2
The flaw in this simplified scenario is that the torque converter is not 100% efficient at converting the power to higher force at lower rpm. It converts a meaningful percentage into HEAT. This is why when you drive an automatic transmissin vehicle aggressively, you heat up the transmission a LOT. This heating up degrades the transmisssion fluid and ultimately can cause the tranny to fail.
High stall torque converters achieve vastly better accleration than low stall (stock) converters via THREE simultaneous effects:
1. The force multiplication described above (which a stock converter also offers)
2. MORE force multiplication than a stock converter, because the higher stall speed enables a much higher RATIO of rpm between the engine side of the converter and the tranny side of the converter, and thus proportionately more multiplication
3. The high stall converter also enables the engine to achieve much higher rpm right away (3000 rpm or more), where it makes more horsepower, and thus has more power and torque to begin with to "multiply". (check out how little power and torque your mighty LS2 engine makes at 1000 or 1500 rpm).
The bottom line is up to a half second quicker to 60 mph, and thus to 1/4 mile (depends on exact stall speed, driver weight, weight of vehicle, etc).
Can you get any multiplication during shifts? Only if the engine speed is momentarily faster than the new gear being selected during an upshift. This happens only if the tranny can shift quicker than the engine can lose rpm. Your 4L60-E tranny (03 / 04 SSR models) or 4L65-E tranny (05 / 06 SSR models) is not a "quick shifter" as delivered from the factory. In fact, it's kind of an underachiever.
A good aftermaret rebuild (like I got) fixes that. I now have more torque multiplication than I want during shifts (breaks the tires loose on EVERY WOT shift), because the tranny IS beating the engine to its new rpm. Becasue I value both my SSR's skin and my own skin, I am taking steps to moderate that via torque management during shifts. It's taking some time, but I am enjoying the process.
I make sure that all testing in this scientific endeavor is done on DRY, STRAIGHT, and LEVEL roads.
if a ssR has insane power (like yours), making it hard to get traction, would a high stall converter (like yours) exasperate the problem?
also do you have a verdict on the rear end gearing?
thanks for all the information
if a ssR has insane power (like yours), making it hard to get traction, would a high stall converter (like yours) exasperate the problem?
also do you have a verdict on the rear end gearing?
thanks for all the information
Yes, a high stall converter does make the traction situation worse, BUT that is only when you really hit the gas hard. I spend the VAST majority of my time driving rather gently, and appreciate the way the high stall converter eases the load on the engine at moderate throttle. What I mean by this, is that my engine is never called on now to produce a lot of torque at low engine rpm (which is hard on an engine in a heavy vehicle), as the converter allows it "wind up a bit". Remember, this is a daily driver, not a vehicle optimized for dragracing.
I am leaning right now toward keeping the 4.56 gearing, as I have realized by doing tire research that the stock Goodyear RS-As on our SSRs are rather low traction tires in the grand scheme of things. A set of Goodrich KDW2 tires would be unattractive to me because of their high weight and significantly larger diameter, but a set of Goodrich KDW (no "2" on the end) look good: 4 lb. lighter each than the KDW2, virtually same diameter as the Goodyear RS-A, and way more traction than the Goodyears.
I have to admit that I need to do SOMETHING, as even moderate throttle now activates the traction control WAY too often.
The diameter and weight are very diffferent, Joe, as I described above. Unless Tire Rack messed up.
Note also that the KDWs are NOT available in a suitable load rating for the FRONT of the SSR. The only sizes close are WAY low on weight capacity. We need a different solution for the front tires.
Time for a teaser on my supercvharged engine too, Joe, as you were the one who got me going on it:
I stated-"what you are saying is that torque multiplication only takes place at the launch and not through some or most of the power band, and never at shift points?"
You said "Yes"
Then at the end of your statement you say - A good aftermaret rebuild (like I got) fixes that. I now have more torque multiplication than I want during shifts (breaks the tires loose on EVERY WOT shift), because the tranny IS beating the engine to its new rpm. Becasue I value both my SSR's skin and my own skin, I am taking steps to moderate that via torque management during shifts. It's taking some time, but I am enjoying the process.
Sooo, are you sure or what???
Enjoy, and by the way, you can make a stock 4l60e shift much firmer and way faster than the way it arrives from the factory. The shops I have talked with about weakness in the tranny was when down shifting at WOT. Mine will mostlikely fall out on the ground tomorrow, but we will see.
Now that you have all of the extra power, any plans on upgrading the breaks.
This is just a quick note to alert Fanatics to an important potential shortcoming in the "torque management" fearure on our SSRs.
The torque management feature is a PCM function that reduces engine torque (and therefore power) during gear shifts, via spark retard and electronic throttle override, whenever the PCM "calculates" instananeously that t
