I keep reading about the Torque Management and how it is holding back the engine.

Can someone please explain how the TQ works with the A4? Is it there to protect the transmission or for Traction Control?

Also, how much hp can the A4 handle stock?

 

Transmission.

Torque is what transmissions are rated for. The A4 in the C6 is rated to 400 lb.-ft. input torque.

 

The 4L60 transmission used in the C5 is rated at 360 lbs-ft engine torque.
The 4L65 transmission used in the C6 is rated at 380 lbs-ft engine torque.
The 6L80 tranmission used in the 2006 Cadillac STS-V is rated at 430 lbs-ft engine torque. There will be 4 variants of the 6L80 with the highest rated at 520 lbs-ft engine torque. The 4L65 will be replaced by the 6L80 transmission in the C6 in the upcoming future.

 

Have a good friend running an ATI Procharger on a 2000 A4 C5. Everything is stock but bolt-ons. He has had no problems whatsoever with his stock internals or transmission.


Dyno TQ numbers on his car: 520/545rwtq


Alot of other people I have heard running 100-150 shots on stock A4 Transmissions and have had no problems either.


But play with fire and you may get burned.

When it comes to mods, you have to realize that whatever you add might cause problems down the road.


Cheers
G

 

Incorrect. The 4L65-E used in otherr applications is rated to 380. The 4L65-E in the C6 and the GTO has been improved to handle 400 lb.-ft. of torque. If the A4 hadn't been upgraded to handle 400, they'd have downgraded the LS2's maximum torque output on the A4 just as they did with the C5. This was covered when the C6 was introduced. Here's an article referencing it:

http://www.superchevy-web.com/tech/0311sc_4l65e/

 

The transmissions are the same, in a truck or in a car. They just say the transmission can handle closer to 400 lbs-ft in a lighter car because the lower mass of the car can accelerate faster with less stress on the transmission's componets. They still have to use torque management to keep the engine's torque within the transmissions limits.

 

It doesn't matter what the car's mass is -- the torque
seen at the transmission input is independent of that,
being a function of the engine's output. The torque
seen at the transmission output is a function of input
torque and gear selection. The only place mass enters
the equation is when acceleration is discussed.

As far as your assertion on using torque mgmt to
limit torque on A4 equipped cars because the tranny
cannot handle rated engine output, can you provide
a source for this? I find this almost impossible to
believe.

Pat

 

The torque the components in the transmission see *is* a function of the vehicle mass under acceleration, which is the only time full engine torque will be applied in a Corvette. If the Corvette were a tractor pulling a stump, then vehicle mass wouldn't be important (except in as so far as it affects traction). But the Corvette is a light passenger car with no towing rating.

Remember that engine torque is only a *potential* until it is loaded to deliver an actual torque. Then F=MA is the fundamental equation, where F is the reaction force to the torque delivered to the ground by the wheel, M is the mass of the car, and A is the acceleration produced by the force.

Let me use an illustration to make what I'm saying a bit clearer. Suppose you have a torque wrench. You put it on a loose nut and pull as hard as you can. Say the wrench is set to "click" at 150 ft-lb. Is it going to click? No. Now run the nut down snug, and repeat the process. Now the wrench will "click". The wrench didn't actually see 150 ft-lb in the first case because there wasn't enough load. It didn't matter that you were pulling as hard as you could. In the second case it did, because there was enough load to resist the full pull. Now with our cars, the load is MA, and the torque actually seen by the transmission can be no greater than that (as scaled by the wheel diameter and diff ratio), no matter how much *potential* the engine has to produce torque.

Now as to torque management, we know that the TCM signals the ECU to retard spark at shift points in order to reduce engine output power during clutch pack engagement. So that torque management function definitely exists.

The TCM *may* also look at line pressure at times other than shift points, and request the ECU to limit engine output. But we don't see that on the dyno, and the only in-car recording I've seen showing that only lasted a couple of frames (50 milliseconds) at one (non-shift) point during a 0-100 MPH run. I don't know what triggered it, but it did show up on the recording trace. (The recording trace actually monitors the ECU, and we can only suppose that it was the TCM which requested that output power reduction.)

The folks who wrote the TCM firmware know, and the folks trying to reverse engineer the TCM firmware will find out, but right now all we have (publicly) are the black box responses we can monitor to try to figure out what is going on with respect to this illusive "torque management" that people talk about.

 

First let me say thank you for an engaging post which
discusses the issue and calmly reasons about them.

I might be dense or I might just be mistaken but I
respectfully don't agree.

In both cases you mention, it seems to me the torque
is being applied. In the case of the car, the full torque
of the engine (assuming sufficient traction) is applied
to the rear wheels. The F=MA relation is pertinent
because the F and M values determine the A.
Consider two examples: car A with mass 2000kg and
car B with mass 4000kg. In each case, the torque
applied to the rear wheels (all else being equal) is the
same. The difference the mass makes is in how hard
the car accelerates. The same torque is applied to the
rear wheels so the same transmission will experience
the same load in each case. Changing the M only
changes the A, not the F. The F is constant. There is
no feedback from the car's mass to the
engine/transmission. They have no way to "know" the
mass in order to alter the torque they apply.

In the case of the nut, the reason the torque wrench
doesn't "click" is merely because your arm, unlike an
engine, can't apply full torque instantly. You gradually
build up the torque over a short period of time but
during that time, the very low M of the nut results in
the nut turning (accelerating) and this turning results
in your arm reducing it's torque application because
you can't easily keep pressure on the torque wrench for more than a half turn or so.

So at the risk of inflaming, I stand by my point that
the transmission sees the same torque regardless of
whether it's in a truck or a car.

Don't get me wrong -- I wasn't claiming TM didn't
exist. I can easily believe it's used for the reasons you
state. I can also believe it's used for emission reasons
as well. I was just expressing disbelief that it was used
to limit engine output in general so as to avoid blowing
up a transmission.

Pat

 

Right from the GM Media Archives:

"...the “L65” is strengthened and revised to accommodate the LS2’s 400 lb.-ft. of torque."

In the C5, the A4 also had torque management which resulted in lower peak torque for A4-equipped engines. Thus the 15 lb.-ft. difference in published torque numbers (360 for the A4 and 375 for the M6.)

The C6 also has torque management, but the A4 engine's published torque is 400 lb.-ft. So either they're lying, or the transmission really is upgraded to handle it (as has been stated by two sources--one of which being GM.) The torque management in the C6 probably pertains more to shifts than to the torque peak.

As for vehicles' weights, the peak input torque seen by the transmission has little to do with it. If the driven tires have full grip, then it doesn't matter what the car's weight is. WOT on an LS2 will result in 400 lb.-ft. of input torque whether you're in a light vehicle or a heavy one. No more, no less. The difference will be seen in acceleration.

 

This may not be answering your questions, but just as an FYI, we dyno tested a bone stock C6 with an A4 and another MN6 and the difference were as follows:

A4:

332 rwhp and 339 rwtq

MN6:

351 rwhp and 361 rwtq

Shawn

 

"They just say the transmission can handle closer to 400 lbs-ft in a lighter car because the lower mass of the car can accelerate faster with less stress on the transmission's componets. " It does seem likely that a heavy dump truck would need a stronger transmission than a light car with both having the same amount of torque output.

Pretty soon the forum will need a resident physicist to guide us on these issues. And throw in a computer science corvette lover.
It's amazing what the internet and The Corvetteforum must be doing to the convolutions in our brain! Andy

 

Thanks for all the feedback,

The reason I bring this up, is somewhere down the road I would like to add a Power-Adder to the car and am considering the Magnasson (?) S/C.

What would I need to upgrade in the A4 and Driveline to deal with a 150hp increase? Will it destroy the transmission?