Torque Converter Question

[ctrlraven]

Now I have a DR tune and have been told my torque converter locks up in 3rd with Dennis's tune and I've heard some other ppl's tunes it locks up at 55mph in 4th. I'm still a newb when it comes to automatic trans because I'm so use to manual vehicles and working on them. I have the just idea of the torque converters purpose but all the 3000-3500rpm stall talk and lock up the torque converter in this gear and that speed has really confused me, can someone explain the purpose of a high stall converter and what the beneifits of the torque converter locking up at above oem speeds will do?

Thanks,
Chris

Sry for seeing like a newb but I always want to understand how things work and what will they do for me before I start moding things I am unsure of.

[MENINBLK]

Chris,

There are 2 ways to connect a transmission to an engine.
The objective of accomplishing this is to do so without stalling your engine
every time you bring the vehicle to a stop.

The original way was a manual transmission with a Clutch.
This is a clutch disc that is sandwiched between the flywheel and a pressure plate.
The clutch disc is connected to the input shaft of the transmission.
As the pressure plate exerts a force toward the flywheel, it pushes
on the clutch plate and eventually locks it against the flywheel.
This allows the engine to turn the input shaft of the transmission.

Then came the automatic transmission.
The Torque Converter works just like a clutch sandwiched between the flywheel and the pressure plate,
except in this setup, all three of these parts are sealed inside the converter housing,
they all have vanes on them like a fan, and instead of applying pressure directly on each other
the fan blades stir automatic transmission oil, which fills the converter.
This works much in the same way you stir a cup of coffee,
except instead of your hand stirring the spoon that stirs the coffee,
the engine stirs the cup (Torque Converter) and the coffee stirs the Stator,
which in a Torque Converter is almost like a clutch plate,
but it has vanes like a fan and only works submerged in transmission oil.

Now here is how we determine stall speed....
We can determine the overall SIZE of a Torque Converter.
We can also determine the PITCH of the vanes inside the Torque Converter.
The combination of the two will determine how much of the rotating energy is transferred
through the spinning transmission oil directly on to the stator.
There is a speed at which you can spin the Torque Converter, and hold the stator still,
until the Torque Converter will not spin any faster.
This is called the STALL SPEED.
Engine size and power also play a part in determining this number.

Low stall speeds are good for around town driving.
High stall speeds are good for launching fast, because the engine can quickly accelerate
to a point where its Torque and Horsepower are higher, and transfer these directly
to the transmission, and ultimately move the vehicle.

This is as simple as I can put it. I hope you understand this.

Now MODERN Torque Converters can also lockup like a Clutch Disc does,
because there is a section of the Torque Converter that works very similar to a Pressure Plate,
and it uses the transmission oil pressure to apply the pressure plate to the stator
so that it can lock it to the Torque Converter, and they spin at the same speed.

Locking the Torque Converter at low speeds (55 mph) has greater gas mileage benefits.
Locking the Torque Converter at higher speeds (65 mph) has greater driveability benefits.
You can choose what you prefer according to your driving style.

I hope this helps a lot.....

[ctrlraven]

Wow, thank you for putting the time into leaving such an information filled post. That def helps me understand things a whole lot better. Thanks Pete! :up:

[sdacbob]

That's about the best description in plain terms of how a torque converter works I ever heard.

[ckadiddle]

Thanks, Pete. I had a vague idea of how things worked, but that makes it more clear for me. Nice explanation.

[Marauderjack]

You have heard the cautions about kicking the car into passing gear with the TC locked (as in stock form or DR's programming).....This puts a BIG strain on the TC since it stays locked when you kick down to 3rd (or even 2nd with the stock tune)!!! Very rough on the OD clutch!!:argue: :help:

The programs with the TC lockup happening only in 4th gear protect against this since the TC will automatically disengage before the downshift......I have tested it time and time again with my SCT and Diablo tunes and it always works as described!!:beer: :bows:

Hope this helps!!;)

Marauderjack:burnout:

[MM03MOK]

Very cool, Pete. Thanks! I agree with Chris. Very helpful in grasping the concept, which has eluded me.

[SergntMac]

Good explanation, well done. Bravo!

Both Lidio and DR sell SCT tuning, and that much of it comes from SCT itself.

I have used both, and the chief difference between a Dennis tune and a Lidio tune, is torque converter behavior, under WOT and at normal cruise.

Lidio will tell you he prefers to leave the torque converter unlocked until late in the game, above 60 MPH, which provides maximum torque conversion values until that speed is achieved.

Reinhart doesn't figit with the SCT base tuning, which locks the the converter after the 2>3 upshift, regrdless of speed. This minimizes fluid temps because until the converter locks, it's dependent on tranny fluid to multiply and deliver torque. It will unlock when your right toe commands it, and in principle, both settings are good. It's a matter of preferrence by the driver.

I prefer the lock-up to come on after the 2>3 shift, and I have my OD set to come on lower than most expect, 40 MPH. The reason for this, is the manner in which I drive my car. Locked and OD on as soon as possible is the way the factory set it up, and it's most economical in city driving.

In WOT driving, such as the drag strip, just shut off the OD, and you're ready, because the tranny will shift just after maximum power has been exhausted in gear. On my Marauder, this is 6200 RPM, and my tranny will hold it's gear to 6200 RPM, then shift. The engine will see 6500 RPM during the shift, but not for long. This is the rationale for a faster, tighter shift reaction that's also a component of the SCT tuning (and Diablo too, I suppose).

To get the maximum benefit from a custom tune, you really need to get a dyno tune. You need to know where your maximum power is delivered, and where it falls off, and adjust the shifting to match that. If you're off, you can "dog" the gear by delaying the shift too long and waste time (and efficiency). Tuning your shifting for peak power delivers maximum power in the WOT 1320/on ramp romps.

Hope this helps, just my .02C

[SergntMac]

You have heard the cautions about kicking the car into passing gear with the TC locked (as in stock form or DR's programming).....This puts a BIG strain on the TC since it stays locked when you kick down to 3rd (or even 2nd with the stock tune)!!! Very rough on the OD clutch!!:argue: :help:

The programs with the TC lockup happening only in 4th gear protect against this since the TC will automatically disengage before the downshift......I have tested it time and time again with my SCT and Diablo tunes and it always works as described!!:beer: :bows:

Hope this helps!!;)

Marauderjack:burnout: If you mean downshifting from OD into 3 or 2, I agree. This will (eventually) wear the OD band and you'll need to rebuild the tranny. This supports the advice to shut off the OD manually before kicking it.

If you really mean torque converter lock-up, I disagree. The torque converter unlocks before the down shift, and without any damage to anything. That's the way it's supposed to work, custom tuning from anyone just tweaks the behavior for efficiency.

If we're speaking of cruising at highway speeds, every time you let off the accelerator, the TC unlocks, and this was why Lidio's tuning didn't agree with my driving habits. I cruise at the speed he set for the lock-up, and it became bothersome to me. Zack readjusted it to lock-up at a lower speed, and it's quite a pleasant drive at 70 MPH.

Truth be known, there's not a lot of deep secrets in the tuning to make one tuner better than the other while selling off the shelf programming. The secrets come on when you get the car on a dyno.

[Marauderjack]

Agreed Mac.....

I have my TC lock at 50 MPH in 4th only......I tried higher speeds but didn't like the in and out stuff either!!:argue:

My interpretation of "OD" is when the TC locks and the engine turns slower than the drive shaft (4th with TC locked?).....With the TC unlocked in 4th I don't think that ever happens so OD and TC lockup in 4th are synonymous...aren't they??:confused:

When I had an older SCT tune the TC would lock in 3rd and when kicking down to pass from 4th gear it would not unlock causing a BIG BOG with my N/A configuration!!:mad: This may not actually be the case but it is how I pictured it and it is 1000% better with the new tuning!!:bows:

Marauderjack:D