VikingTrad3r

Hi guys.

My understanding of what a "stall speed" is, is that rpm where the clutch in the tc will lock up. or, be at 1:1 ratio to the input shaft of the trans. Forgive me if my terminology is off, learning this as i go, but from what i have read and watched, this is what it means. Is this correct?

If there is a tcc solenoid and the locking is controlled by the ecm then why is there even a stall speed rating?

Like, shouldn't the tcc just tell it when to lockup? So then what relevance does the "stall speed" designed into the torque converter even have?

Could somebody help me understand that?



The reason I am asking is because my TC on my 85, which was replaced by a previous owner back in 2009, always locked up into 1:1 way way too early. OEM stall speed on the 85 was 2056rpm.

I am looking to replace it with an OEM one and I went to rock auto, and the only one they sell for the 85 says it is 1400stall speed. That got me to thinking, if a previous owner did some transmission work on this car and they put a 1400 stall speed on this car, would that cause it to lockup much earlier than a 2056 rpm stall speed that the car was designed for in 1985?

Thanks for the help in understanding this stuff.
Part of me thinks if the ecm controls the lockup, then who cares what the stall speed is. I just don't have clarity on how it works.

VikingTrad3r

so the ecm will "allow lockup" via tcc solenoid whenever it sees fit, but the stall speed rpm of the hardware, the torque converter, would prevent lockup before the stall speed even if the ecm "allowed it" earlier? is that right?

VikingTrad3r

thanks bow tie. aaa hhaaa.

so, when u say "moves from idle", you mean like put the AT in any gear, and from a stand still if you let your foot off the gas and it moves forward then its a low stall speed?

im starting to get it a bit. a higher stall speed should mean that, from a stand still, the rom of the engine would rev up to 2000 (on a 2000 stall speed tc for example) before moving forward? and it has to do with the pitch of the fan/turbine blades inside the tc.

but if my cars all creep forward from just taking foot off the gas wouldnt that mean they all have really really low stall speeds?

jsmn4vu

Hold the brake while stopped and in gear; gently add power and RPMs will increase easily up to a point at which further increase takes a disproportionate amount of throttle. That will be the approximate T/C stall speed.

Tom400CFI

Stall speed is the speed where the engine can't rev any higher, while the car is stopped. So in a "stall test" you would plant your foot on the brake, floor the throttle. The RPM the engine peaks at, is your stall speed. This test would be hard to perform in a decent running C4; it would likely spin the tires before reaching it's stall speed. In a **** box? Easy test to perform.

SECOND PARAGRAPH

FIRST PARAGRAPH

Tom400CFI

Yeah...that's not accurate. In that case, it the "stall speed" of a converter would be ALL RPM, because the converter transmits power at all RPM...and consequently, will "move the car" at any RPM...even idle. At what RPM, does the converter NOT transfer power to the trans? None. If the thing is rotating, it's "transmitting power". Banks F'ed up on their verbage on that poorly written page. Read the page that I provided from the converter MAKER...not the converter re-seller.

Set your vehicle up so the tires can't turn. Put in gear, floor the throttle. The max speed the engine achieves; THAT is your stall speed.


.

jsmn4vu

The Banks Power article isn't as accurate as it could be, because it doesn't make it clear that the torque converter will transfer power well below stall speed. Try this one, instead:
https://en.wikipedia.org/wiki/Torque...ational_phases

Kevova

Stall speed is maximum rpm engine reach without car moving. Set parking brake, place foot firmly on brake pedal, then depress accelerator pedal until max rpm is reached - that is the stall speed. Trans fluid is going to heat up quick so it is a 10-15 second thing then engine has to idle allowing ATF to cool down. In some cases if car creeps ABS/TCS can engage causing brakes to release leading to a"Big Eyed Moment" Stall speed is controlled by the design of the fins internal to the torque converter.

Since the early 80's TCC is controlled electrically by a computer with MPH and engine load inputs. Most torque converters have a single surface hydraulic clutch and piston assembly on the flywheel side of housing. Solenoids that control them can be on /off or ""Pulse Width Modulated" (digital for lack of a better word). Solenoid directs fluid to TCC piston within converter housing to contact turbine eliminating slippage common to all hydraulic couplings.

Christi@n

Stall speed as far as i know is all that part before torqe converter reaches its full fluid coupling, In other word, since torque converter has about 10% of efficency lost, just as instance if impeller spins at 100 rpm turbine will spin at 90 rpm.
In this situation stator and fluid inside are rotating at same speed, could be 99 rpm, so this case converter is considered to be fluid coupled.

The different situation is before fluid coupling is reached, in this other case impeller spins at 100 rpm stator multiplies torque from 1.2 to 1.5 time the input shaft and turbine spins slowly then first case above, could be from 0 tp 85 rpm. This case we have a great heat dissipation.

From when you turn on engine to the converter fluid coupling situation, this is stall speed.

When converter clutch is engaged we have anymore a fluid coupling, but a soild coupling

Tom400CFI

The coupling of the converter is never a "solid coupling", except when the mechanical clutch is engaged (lock up). Fluid couling is simply a term used to describe a power transmission device that uses fluid to transfer power. A boat propeller in water is a "fluid coupler", of sorts. You don't need specific RPM, or RPM differentials to achieve "Fluid coupling".


While that is true (only b/c the input shaft is turning so slowly at that point), that is totally different than:
Guys, read the links I provided. Let's say the OP's converter stalls at 2200 RPM in his car; At WOT, in gear w/the wheels locked, his engine can spin the converter to 2200. He has a "2200 RPM stall converter". Now lets that that converter out of his car, and put it in a big block drag car and re-run the test. Is it going to stall at 2200 RPM b/c we have "fluid coupling" at some RPM or something? NO. The big block, with it's higher torque, will push that converter to a higher speed, before it's maxed out. Now all of the sudden, in a different car, our converter is a "2700 RPM stall converter". The stall speed isn't hard and fast, it's an estimate based on average engines it may be used on. You'll never know the actual stall speed of a converter, until you put it in YOUR car, lock the wheels, put it in gear, and floor it...see what the RPM. There is your stall speed.

VikingTrad3r

I think I am starting to get it.

so why wouldn't we want to have a tc with a higher stall speed?

is it because the engine would always be revving a bit higher? but at the same time we'd be in the "power band" a lot more of the time right?

jsmn4vu

You've got it, and that's the reason high stall speed TCs are used in performance applications. The tradeoff is fuel economy, which is why low performance cars typically use TCs with a low stall speed.

Tom400CFI

The primary reason why you don't want a converter w/a higher stall speed is the loss of efficiency. A "looser" converter (higher stall speed) will allow a greater RPM differential (crank RPM, vs. input shaft RPM) than a "tighter" one. How does that RPM differential, that "looseness" manifest itself? HEAT. All the slippage in any converter is turned into heat (why auto trans' need coolers). The more slippage we allow (which is what gets us our higher stall speed), the more heat we build in normal driving. That heat IS, inefficiency. We're turning HP into heat, rather than forward motion.

The lock up feature mitigates this issue by mechanically locking the input and output of the converter. But in all driving modes where the converter is unlocked, you're drive a boat with "too small a propeller", so to speak. Some people don't mind it, others find it irritating.

Another "problem is if you combine a high stall converter, with a low RPM motor. Then you're missing out on the low end tq that the engine can provide, but you're not able to exploit the high RPM potential of the drive system, b/c the engine won't go there. So, typically, tight converters are couple to "low end TORK MONSTERS" and loose converters are coupled to "high RPM screamers". Typically.

Tom400CFI

Totally depends on the weight of the vehicle, first and final gear ratios, etc. IOW, how easily (quickly) the input shaft accelerates away from stationary.


Basically. This guy can explain it better than either if us, though....

Christi@n

Cons are
Higher stall speed is higher "slip sensation" and a little bit more "lag" if i'm right,

Is these two works for you

Pro should be car is always close to the maximum torque N power, in high rpm stall converter, think car makes big whooaaaa before to move

Christi@n

Yes is just a term, but thinks it works well

Take a looks this video they explain very well how it works...i've understand a lot of that video, that don't speak american :english so well

Tom400CFI

Thanks for the vid...I'm already well aware of how a converter works, however. I actually cut a converter open, and gave a presentation pretty similar to the video, back when I was in automotive school.

Kevova

With TCC you could get away with high stall converters because of lock up. A minute ago a street car with 4:11 and 3-3500 stall converters could be daily drivers. No TCC or O/D turning 3k all day passing everything but a gas station. TCC may have cut RPM down to 2500. Only thing is heat. Powertrain cooling today is designed for TCC and may not be adequate to cool fluid. ATF now is 100% better than it was back then.

VikingTrad3r

Thanks Tom.



So then, for my 85 which had a 2000 rpm stall speed from factory, going with a 1400 rpm stall speed replacement would be allright? this is the only available option from rock auto. im sure i could get a 2000 from a local supplier but i am ordering a flywheel from rock because of the of the price and thought i'd get both from the same place.

sounds like the only thing the higher stall speed would give me is when the trans up shifts i would stay in the power band a bit better. i can imaging somewhere between the stock and the 1400 would be great.

then if you want to set your lock up to engage a bit earlier, then you could avoid driving around town slipping in the tc all day long during slow accellerations.

maybe that is what they did here with this car....maybe they installed a high stall TC, then lowered the lockup in the tune.

Christi@n

Was not for you that video Tom... was for VikingTrad3r.....