Please describe how a torque converter works, and how higher stall works

[DocMel]

Plz keep it simple for the simple mind:  How a tourque converter works, and also how a higher stall helps with bigger cams, with 323 rear end:

Ive got a slighter hotter cam in my stock 440.  Rears are 323's:    I need a higher stall converter as the stock one is really a pig at take off, but I first want to know the theory about how they work, and how to determine what stall I really need \\\Plz keep it simple for stupid...........

[Chryco Psycho]

basically ithas no mechanical link , it is just 1 fan blowing into a second fan but using hydraulic fluid instead of air , it is the size & design of the fan that slips until enough hydraulic pressure builds up to force the second fan to move . A higher stall allow the engine to get into a higher RPM powerband before it puts load against the engine so if the converter is too low stall the engine is loaded before it can get to its powerband causing the car to perform poorly , with the high stall the engine is well into the powerband before the engine has load allowing the car to move easily once the converter transmits the power .
 Basically if you look at the powerband of the cam & intake & add about 400 or more RPM the package will work well , so if your cam starts making power at 2000 rpm you need a 2400-2500 stall

[Bullitt-]

ACC will make a recommendation...just fill in the info

http://accperformance.com/Order/index.html

Ordered mine from http://www.murphysautomotive.com/
Be sure & ask "for today's SPECIAL PRICE"....saved me another forty bucks

[burdar]

The fan analogy is a good one.  Most people can understand the concept if it is described that way.

Imagine two fans facing each other.  Turn one of the fans on.  The air that is being pushed by the first fan will start turning the second fan.  That is exactly how a torque convertor works except trans fluid moves the second fan instead of air.

The outer torque conv. housing (first fan) spins at engine RMP because it's bolted to the flexplate.  The part of the conv. that is splined to the trans input shaft is the second fan.  It is not mechanically tied to the crank so it doesn't always spin when the engine is running. 

At idle, there isn't enough fluid pushing against the second fan to get it spinning.  As RPM increases, so does the flow of trans fluid into the second fan and it starts to spin.  The second fan is splined to the input shaft of the trans so when there is enough fluid pressure, the car starts to move.

[Cooter]

NO! Contrary to popular belief, they do NOT rev up and slam into gear at 3500 RPM (3500 stall)..


Up to a certain point, most people will not even know there's a stall converter in the car/truck, until the loud pedal is pushed and the torque is multiplied greatly and the tires go up in smoke....After about 4000 RPM stall speed, the trans begins to feel as if it's slipping when you step on the gas, then you step down a little further and the car/truck begins to move...Another good analogy is think of a Water wheel on an old saw mill/grain mill, etc.
Now, with the blades in the wheel at  flat angle, the wheels turns with little water flow..Angle those blades more towards the rotation of the wheel, and all of a sudden it takes more water at a greater speed to turn the wheel..

[72cudamaan]

    Who said anything about slamming into gear. Did you even read the posts?

[500Stroker]

Mopar Enthusiast article

http://editions.amospublishing.com/mpre/default.aspx?d=20080401&page1=74&pagenum=75&f=1&f=1&id=5e0d8d52-c564-4a0a-ab2f-4e2b55714725

[Cooter]

    Who said anything about slamming into gear. Did you even read the posts?

I was making a funny....Guess I shoulda used a smiley ...Sorry..

[willy]

Just a question for my understanding.... Can you cruise/drive a car at 2000 rpm if you had lets say a 3500 stall? If not, is a stall is over 3000 rpm is it streetable? Thanks.

[Aussie Challenger]

Simple answer is yes but it will feel like the clutch is slipping and you will get poor fuel mileage.

[Sean]

No transmission expert here so someone correct me if I'm way off...

Once your car is moving, it wont take as much air (using the fan analagy from above) from the first fan to keep the second fan moving.  However, if you stomp on the gas at 2000 RPMs while cruizing, you wont be transfering max power to the second fan until you hit 3500 RPMs.

Sean

[Cooter]

Yes, you would be correct on that one...

Well, you may notice a small RPM change cruising at 2000 with a 3500 RPM converter...Not much though..I draw the line at 4500 RPM's on the street. I had about a $750.00 4500 RPM converter and it never actually got locked in just cruising with 3.73 Gears.(Mustang GT with 302, and C4).. I'd burn the fluid BLACK going to town..(25 miles)..But, that thing was a beast for about a car length, then I was out of motor...

The Biggest Change when going from stock to say a 3500 Converter is the WOT throttle stomp from a dead standstill..Your tires will go up in smoke without traction aids...However, there are converters today that are rated at 4000 RPM's, but will "lock up" with the help of a lock up clutch for the newer O/D transmissions and are just like having a straight drive when locked in..(Small clutch inside converter that is hydraulically locked by a switch)

The one thing you do not want to do is run a NON-Lock up High Stall converter with an Overdrive trans.
The converter will never quit trying to multiply the torque when in the tall Overdrive gear, and will overheat the trans fluid cooking the trans.

High Stall converters are constantly slipping to a degree..About the only time they are most efficient, is when you are up in the RPM's..Ever heard a race car When it's coming back down return row and the driver kinda tries to "Hop" the car?  A stock car just kinda lugs and every time the gas is hit it tries to take off emediately, where the race car revs Like WAAA! WAAA!

The "Flash" stall of a converter is where it will go in RPM's when you are on the brake and just blip the thottle and see where the car will rev to and no more. In a stock car, the tires will probably not begin to spin at stock stall speed. The car just kinda revs up to a certain point and it won't rev any more beyond that. Around 1800-2200 depending on stock converter...

With a high Stall Conveter, the car tries to rev to the say 3500 RPM stall speed, but the tires usually break loose before it gets to it as the amount of torque being multiplied has almost tripled..

Another way to explain this would be the Diesels...Ever been in a diesel truck? How bout when you get on the thottle and the truck acts like it doesn't want to move until you've rev'ed it a bit high? that is what a High stall converter feels like. Would really need to know your cam specs and the powerband of the cam before I could tell you about the stall speed...If the range on the cam was 2500-5500, then I'd recommend a 3000 Stall.

[72 cuda]

Cooter,
thanks,hell I didn't even know how to pose the question!
this list is awesome!
Again thanks, now I can get to scheming  

[Sean]

Thanks guys!  I learned a lot fro m this thread.

Sean

[1970 RT Challenger 1970]

Is there a quick and dirty way to determine your stall speed of the converter without dropping the tranny?
Say simply by applying the gas and watching the tach?