Correct Stall Speed?
 

I was perusing the FSM for my '90 SR5 4x4 pickup and read the section about the converter stall speed. It says that it should be 2,850 RPM. (3vze-A340H trans) and my truck stalls @2,300. This is an all stock truck in excellent running condition.
What do you guys' trucks stall at?
Thanx,
Bud

Man, i thought we were gonna talk airplanes......

2850 sound high to me... i thought it was 2300-2500 to me

Just out of curioisity, how does one check the stall speed?
(of a vehicle that is)

a 2800rpm stall sounds VERY high for a 3.0......but if that's the case, that's why most poepel think the 3.0 is slow! The TC doesnt get efficient until 3krpm!

You put the vehicle in "D", hold the brake tight and and quickly, but not too abruptly, mash the pedal to the floor for just a few seconds and record the RPM's.
That is the best way to do it.
The wheels should be chocked as well but remember, these 3.slows aren't going to bust the wheels loose anyway :(
FYI..I used this for the stall speed referencehttp://personal.utulsa.edu/~nathan-b...35mechanic.pdf

Thats what i have done in the past... but very few rigs will break the tires loose, out 325hp big block burb wont even do it in 2wd low... You also dont have to go full throttle.. just apply gas until the rpms dont climb anymore.

Wanna bet? :D

http://vids.myspace.com/index.cfm?fu...eoid=908314682

3vze with the slush-o-matic! Truth be told the rear tires were wet the front weren't AND i only have drums on the back end. On today's vehicles doing this is extremely hard without a line lock due to having rear disc brakes which are uber strong compared to drums...

Gotta love wet pavement :)

Yea I am completely lost in this thread. The only way I know how to check stall speed in pull the yoke back and wait till the stall alarm goes off and you feel all funny inside.


Is this an AUTO trans thing only??

si! All automatic transmission have torque converters (TC) which are a viscous couplers that have a stall speed where it "engages." (no mechanical engagement) All TC's tend to lock up at about 40-48mph and provide no driveline slippage....(this is the mechanical engagement)

But having a high stall speed allows the engine to flash into the bottom of its power band (ideally) when the TC "engages." LS1's (GM's gen III smallblock) typically has a stock stall of 1200rpm. Most people put a 3000-3500rpm stall in it so it hits its power band from right off the line.

This is just like revving your motor to the bottom of its power band with your manual and then quickly slipping the clutch. Pending the amount of power applied and the rate of slip you either launch HARD or spin the tires.

What determines the "stall speed" is the amount the fins inside the TC are bent. I am good friends with the owner of the ONLY torque Converter repair shop in Kansas. Apparently, it takes a great deal of experience to know just how much to bend the fins. Hiriden

Both are kinda, sorta right ;)

There are two "turbine" disks in the TC that look similar to the turbine blades in a jet engine. One of the disks is basically attached to the input end of the TC and the other disk is basically attached to the other end of the TC (this is a simplified explanation).
As mentioned, fluid flows over one, causing it to spin which causes the fluid to rotate causing the other side to spin (viscous coupling).
Now, stall speed.
Fluid can only flow so fast (much) through any given size opening, the larger the opening the faster (and more volume) the fluid can flow through it.
Make sense so far?
Anyway, when you have the tranny in gear and the brakes on hard, you're preventing one side of the TC turbine disk from spinning. The fins in the disk create openings that the fluid flows through, right?
Now, by preventing the disk from turning we are measuring how fast (much) fluid can be moved through the holes. The larger the "hole" (that is the more openings in between the turbine blades and/or the larger the openings), the faster (and more) the fluid can flow.
That's simply what the stall speed measures. The amount of fluid flowing through the fixed turbine disk. Once the disk that's spinning moves as much fluid as can flow through the "hole" in the other disk (which isn't moving) that spinning disk won't be able to spin any faster. That's the "stall speed".

The A340's in our applications (in the 3.0) have a 2800'ish stall speed.
Generally you want to stall speed to be around the start of some sort of power band for the engine.
The TC also has a lockup clutch, which is very similar to a regular clutch and has basically the same frictions as the clutches in the auto tranny itself.
When the LU clutch is applied it effectively locks both the turbine disk together such that there is no longer any viscous coupling action.
BTW the two ""turbine disk" are called the stator and the turbine.

The computer in the 4Runners have a pretty sophisticated lockup program.
It will lockup the TC in both 3rd and 4th gears, so the "high" stall speed doesn't present any real problems, efficiency wise.

You can get a TC made for just about any stall speed that you could want.
The main difference that you'ld notice is the diameter of the TC itself between high and low stall speeds.

The "high" stall speed of the TC's in our 4Runners really makes rockcrawling type wheel much easier. The TC provides an almost infinitly variable "crawl ratio".


I owned a transmission shop for several years ;)


BTW, the people who drag race usually have a TC with a stall speed that's right into the power band of the engine. That also have a valve body in the tranny that has a transmission brake. This is basically a fluid circuit that clamps the low drum band to the low drum.
You drive up the the lights (tree), apply the transbrake (with a switch) and floor it. The engine will reve up to the stall speed of the TC, set to be right into the power band of the particular engine. When the lights go green you simply flip the transbrake switch off and you launch.



:)
Fred

wow, very detailed Fred, great work! At any rate, changing the angle of the fins to allow more, or less fluid to pass through at a greater or more inhibited rate is what changes the amount of stall any particular TC has. :-)

But it's more than just changing the fin angles usually.
Look at two TC's for the same tranny, one low stall and one high stall and you'll see that they are different diameters.



:)
Fred

the bigger converter will ahve hte higher stall speed?

so, 2300 is NOT correct for this application. I guess I wil be putting in a TC at a later date.
Thanx:)

No, actually higher stall converters are smaller.




:)
Fred

If you're happy with what you have, I wouldn't worry about it.
Is the tranny acting fine ?


:)
Fred

Tranny shifts flawlessly. Lockup runs about 400 RPM less than the "usual" R's. Freeway speed @ 70 MPH is around 2600 RPM under lockup so I guess alls well. I was just concerned that the 2800 RPM number is so much higher than the 2300 I am getting. One caveat, however, is that less slippage=cooler trans temps so I guess it's a tradeoff, eh?
Besides, no matter what you do to the 3VZE won't really bump up the H.P. or the performance anyway.
Next stop..the 3.4 :)