Raspy

Lockup means no fluid coupling. It's a clutch engaged with hydraulic pressure. No slipping unless it is overpowered by the torque from the engine.

Wetspirit

Raspy

[QUOTE=RowJ;1500577]This might help.....
Let’s start with a TRUE FULL STALL SPEED. If the transmission were in drive, the brakes were held down (so the vehicle will not move) and the throttle was held "wide open" the torque converter will "stall" the engine at a certain rpm. When "stalled" the engine will not be able to spin any faster unless the vehicle is allowed to move. This is a TRUE STALL SPEED.
Do not test for True Stall Speed... it can damage shafts and overheat your Tq Converter!

The next stall speed is generally called BREAK AWAY STALL SPEED. If a truck is stopped on a hill and held in position using light throttle we are almost at the "break away" stall speed.
The Break Away Stall Speed is the RPM required to start the truck moving.

The last stall speed is generally referred to as the FLASH STALL SPEED. The flash stall speed takes effect under hard acceleration. If, from a standing start, you were to "floor" the throttle the engine would start to accelerate quickly and then pause at an rpm as it starts to pull the truck. If the engine went from idle to 1500 rpm in 1.5 seconds when floored and then took another 2 or 3 seconds to get from 1500 to 1700 rpm, this would mean the "flash stall" speed was at 1500 rpm.




Nice explanation!

Wetspirit

AlpineRAM

The point in stall speed is also that for example for maximum acceleration from standstill it would be perfect to get the flash stall just at peak horsepower- power is the capability to do a job quickly. But with the example above it would snap your neck from the line but it would fall on it's face from there on.
The point is that with the CTD you have masses of low end grunt and the stock TC is only starting to pull right when you are above max torque rpm. With a lower stall TC you lose a little startin acceleration but get into the powerband after some meters. Over all the lower stall TC will give you better acceleration. The downside with a turbocharged diesel is that at low engine rpm it's difficult to get the turbo to spool quickly, so the factory TC allows you to rev your engine a bit more to get the turbo to spool quicker and reduce emissions. But since everybody and his dog on this board who is concerned about a TC has either plugged in some electronic gizmo that allows for more low boost fuel or has turned some adjusters, ground some plates etc on the mechanical pumps to do exactly the same the factory TC will not match the new torque curve.
Any stall speed is the point where the input torque from the engine will be the same as the load generated by the TC (at full stall for an output shaft speed of the TC of zero) - so if you change the torque you change the stall speed. If you look at a torque curve you will also see that the curve starts to fall after peak torque- so for the stock TC you are usually above the peak torque. If you take a 12V with just a governor spring kit the stall point rises drastically, simply because now there is much more torque from the engine at the old stall speed. (The engine has already started to defuel at the stall speed stock, but with the GSK it doesn't) eg with the 98 12V the peakl torque of 420 ft-lbs is at 1500 but at the stall speed of 2200 you're at roughly 360 ft-lbs. With the GSK you will still have 420 at 2200, so the capability to generate 360 ft-lbs of braking power (as seen from the engine) will not stop the engine reving further.
A very interesting point is the map that shows the torque multipliation at certain rpm differences for a given TC- Some TCs with milled stators would give you a lower stall point than stock but their benefit isn't too great- they would stall at peak torque but only multiply it by 1.3 instead of the stocker at roughly 1.8 at 2200- so with the milled stator we have 420*1.3= 456 ft-lbs going into the tranny whereas with the stocker we have 360*1.8=648 ft-lbs. But why do people like tose milled stators? simply because with the stocker you will pull good for the first couple of meters but with the vehicle accelerating you get to rpms where the engine hp starts to fall rapidly before the tranny does upshift- with the milled stator you get into the powerband after you start moving so you get quicker acceleration.

So now I've added some more confusion to the topic

AlpineRAM

HOV

At least I understood that last sentance!

AlpineRAM

I just wanted to show that there is no such thing as a fixed stall speed- if you change the engine parameters you change the stall speed.
And I also wanted to show that there is soo much more to it than stall speed. The TC has to be matched to the engine, gearing, shift pattern and the usage of the vehicle.

AlpineRAM

XLR8R

Great explanations, guys!

Alpine - that's why I don't like the stock converters behind the CTD; with plenty of off-idle torque, that much multiplication through the converter isn't needed IMO... I'd rather have a tighter TC - better acceleration, less heat and mileage gains to boot.

I prefer a converter design that incorporates a stator with blade shapes/angles to promote high torque multiplication, yet manufactured with very tight tolerances for the turbine and stator so slip is minimized before lockup is engaged... guess I want the best of both worlds!

No wonder I prefer a manual tranny - fewer mental gymnastics...

BTW - the HPCR torque curve is pretty flat - 90% of rated torque from 1600 - 2900 RPM; that's why I think there's even more reason to choose a converter wisely for a 3rd gen.

AlpineRAM

XLR8R - I think that with the HPCR in stock form it's easyer to choose a TC.
I'm running a DTT TC and really like what it does- I've tried several different other brands that just touted "low stall" and whatever kind of cover for towing etc. They needed more go pedal to get rolling and lugged the engine for a long period while accelerating.
With mine I've got very high torque multiplication and a lower stall speed (especially flash stall) than the stock TC with the stock engine. (And AFAIK the smarty + Mach3s do add a tiny bit of torque )
I understand your point of less mental gymnastics with a manual- but try to teach an idiot to shift correctly and especially always chose the right gear. Now you're in the realm of powertrain programming

AlpineRAM

XLR8R

In the old days it seems standard transmissions abounded, and we learned early (usually 1st) to drive with them... nowadays, slushboxes are apparently de rigueur (they've come a long way, baby! )