Torque Converter Talk

[Billydelrio]

As I understand it, prior to 1992, the majority of the small diameter racing torque converters used factory stators that were "machined down" to fit the particular converter core. Now, there are suppliers of aftermarket stators for several core sizes.

Is it possible that a factory Super Stock converter (2466323) stator was machined down to fit an advertised 7" racing converter core. If this is the case, would the performance be as I described in Dr. R's post. Meaning, the converter stalls to 5600 under any condition, behind multiple engines of different cubic inches and characteristics.

It seems to me that the machining of the stator will drastically reduce the stator's ability to "catch" fluid from the turbine and redirect it to the impeller. This will give a near zero torque multiplication factor. But why will the converter have a "brick wall" at 5600 and not vary from that with different torque inputs at that rpm?

As A Warren Wallace said: "Sometimes you have to reinvent the wheel, at least in your mind, for if you don't understand how a wheel works, how do you fix a wheel that doesn't work? If a wheel seems to simple, try a torque converter."

Also, would this same converter absorb enough power to create a loss of one second to the 1/4 mile et?
Billy

[bbaspense]

Unless you are running 9's...why would you need a 5600 stall converter.

An under powered car would make that converter slip all the way down the strip.

Not many 10, 11 or 12 second cars would have a peak torque reading at 5500rpm.

I would see the loss of ET in slip and because the car would be trying to leave above the peak torque of the engine.

The heat produced by this converter would be unbelievable in an under powered vehicle.

Jason

[Billydelrio]

Jason, I run a 273 that makes peak horse power near 7000 and torque near 5800.

What I am trying to do with this post is learn more about the dynamics within the torque converter. I believe this is an interesting topic.

Why would the converter slip if the car was under powered? Why would it not slip more if the engine produced more power? To me, these are interesting questions.

Thanks for the reply.
Billy

[GTXMONTE]

If a convertor went to the same rpm behind any motor combo, that convertor was broken. A convertor multiplies torque, you put it behind a motor that makes a lot of torque it stalls more, no way around that. A broken piece could surely slow you down a sec or more. As for why a low HP motor slips a convertor worse, the motor is not making enough grunt at the convertors stall point to "lock" the convertor, so it slips constantly, building lots of heat. A good convertor builder can build you one based on your combo that will be loose enough to get you off the line and that you will not "drive through" at the top end. Knowing just which stator to use or building a custom one and how to pitch it calls for years of experience and is why a "good" convertor is expensive.

Monte Smith

[Runner1971]

I like this topic as well, what exactly is meant by the torque multiplication, will this give you more torque at the rear wheels that you woulda gotten from a manual trans? or just more torque than a cheaper converter?

[Billydelrio]

I am trying to learn, so forgive me for trying to argue this point.

Question: If the engine is not making enough grunt to "lock" up the converter at stall speed, then why does it not just slip on to a higher stall speed?

Question: If the sprag is holding and overrunning as designed, could an improperly modified stator cause a power absorbtion(heat build up) to take place? Why?

Billy

[72Bird]

This is related although a chebby story. My buddy has a Chebelle. He blew the tranny when we were in high school and decided to put a higher stall in it while it was out, and being rebuilt. He bought a used 10 GER(Junk)unit from a fellow in town. The fellow stated that the converter was in good shape, just too much stall for him. I will never forget when we went to pick his car up from the tranny shop and he backs out. Sounded like really bad slipping clutch. He had a stock 305 with headers,intake, carb, the usual hop-up stuff with 2.73 gears. This motor had no torque at all. Well, this converter would flash around 5500-6000. The funniest thing, it would haul ass to around 40mph and that was it. When you would shift, RPMs would dip to maybe 5300. The Chevelle would normally run high 15's to low 16's. With this converter, it would easily take my RR to about 35mph, but that was it. Needless to say the thing was junk, and was taken out very quickly.

As long as were on the subject. I dont understand, Just what is stall speed with a converter? Why is it that when you build a monster engine, you need to change the converter to 1 with a different stall? Does that mean it slips more at a lower RPM? Can someone break this down into simple laymans terms? Thanks

[Billydelrio]

Tucks 300, Suppose an engine makes good power and good torque a little above idle rpm. It would then be ideal for that engine to move the car at a lower engine rpm. This requires a "stall" speed that is very low, in the order of 800 to 900 rpm. This torque converter will allow the engine to work at low rpms.
If the engine has been modified with a cam, valves, headers,...etc. the power of the engine may not be diddle until the rpm reaches, let's say, 4500 rpm. In this case, it would be advantageous to have a torque converter that is loose (slips) all the way to 4000 or so before it stalls (holds). The engine is now being used at the start of it's good power band.
You could say that stall speed is the rpm at which the car starts to move.

Billy

[Billydelrio]

72Bird, when you say "junk," did you mean that it was broken or a poor design? This is the type of information I am looking for.
Thanks,
Billy

[HOLESHOT]

GOOD TOPIC,I THINK WE MUST GIVE CONSIDERATION TO FLUID DYNAMICS WHICH COME INTO PLAY BASED ON STATOR DESIGN AND ENGINE IMPUT.AS DEMAND GOES UP FROM THE CONVERTOR WANTING TO GET TO ITS LOCK UP THE DYNAMICS OR VORTEX OF THE FLUID DOES NOT STAY LINEAR DUE TO AREATION,TORQUE FLUCTUATIONS,OIL VISCOSITY CHANGES FROM HEAT AND FRONT PUMP LIMITATIONS.DUE TO ALL THESE VARIABLES EACH CONVERTOR WILL VARY IN ITS ABILITY TO PERFORM IN DIFFERENT COMBINATIONS HENCE THE 3-3500 RPM RATINGS FOR IE.WHEN YOU BY TRANSMISSIONS FROM REPUTABLE BUILDERS LIKE ART CARR,DLI ETC PUMPS ARE DRAMATICALLY MODIFIED TO CREATE BETTER PRESSURES AND VOLUMES FOR SPECIALTY CONVERTORS.MOST OF US INSTALL THESE CONVERTORS ON RELATIVLY STOCK TRANSMISSIONS MANY OF WHICH HAVE WORN INPUT SHATS AND PUMPS.

Billydelrio- If I understand right, stall speed is the rpm that a converter max's out at in either a stk. or mod engine? say 4500 compared to 6500 RPM. From what you said, it would seem to me that you'd have to give it more gas to get the car rolling, true statement?

[72Bird]

Billy,

I meant junk as in broken and bad design. I would never buy anything from GER. I know of a few people who have had good success with them, but mainly horror stories. For instance my buddy has a 70 Stang, and he ordered a GER C-4 and 10 inch converter. I built him a new aluminum headed 351 and we put all of it in at once. We broke the cam in and decided to drop it in gear to see what the idle characteristics were gonna be. Well we had no gear. Tried all of them, nothing. Drained the fluid and it had cooked itself while we were breaking cam in. Called GER and talked to their "Tech" man. He said the usual, converter wasnt properly indexed and tore the front pump off line. Well, I know it was properly indexed because I measured the distance from bellhousing to converter and even called two local tranny shops to verify depth. The converter was easy to bolt up and no problems were forseen. Well my buddy had to pay 125 to ship the tranny and converter back to them, then another 150 to rebuild and ship back. It was truly a nightmare. They wouldnt stand behind their product at all. I have since heard of many other similar stories involving GER. Just my .02
Bird

[GTXMONTE]

Originally posted by Billydelrio:
I am trying to learn, so forgive me for trying to argue this point.

Question: If the engine is not making enough grunt to "lock" up the converter at stall speed, then why does it not just slip on to a higher stall speed?

Question: If the sprag is holding and overrunning as designed, could an improperly modified stator cause a power absorbtion(heat build up) to take place? Why?

Billy

A convertor does not stall infinitely based on the amout of power you put to it. At some point the design and the vane pitch take over. The reason a low HP motor wont lock a loose convertor is because that motor is making no torque at that rpm. They are designed to slip until the range where the motor makes torque(say 4500) but you put that convertor behind a motor that makes peak torque down around 2000, by the time that motor gets to 4500 it's all done no "grunt" so it can't make the convertor work. In theory the convertor should lock at its given rpm even behind the low HP motor, but in the real world that loose convertor has been slipping so long trying to get to it's lock point that the fluid is so hot and aerated that it can't. Boy this stuff is hard to explain, we really need a couple of engineer types here. I know how it works, just having a hard time trying to explain.

Monte Smith

[cdignition]

I dont think the converter actually "locks"..its more of a "gets so tight that it dosent slip so much" kind of deal, at the big end. Its whats known as a "fluid Connection" of the trans to the motor.

[dartmeister]

This is getting interesting. More! More!

[Billydelrio]

Yes, it is hard to explain!
As engine rpm rises, the impeller puts more and more centripital fluid pressure upon the turbine(turbine is not moving). When the impeller and turbine pressures become stagnant, this is the stall point. (the engine can't force the impeller to provide more fluid pressure) That was the easy part. Now let's add the stator to the equation. The stator is going to catch the fluid passing the turbine at a particular angle and turn it into the impeller. The stator is mounted to the sprag and is being forced in the direction that it can not rotate. The stator itself, in this case, is not an energy consumer, therefore all the fluid energy is being redirected back into the impeller. This assists the impeller in providing fluid pressure to the turbine. The amount of the stator assistance determines the torque multiplication of the torque converter unit. The stator shape (radius of curvature and length) is what I am calling the most important dimension in the torque converter.

GTX I agree with your statement that a converter will reach a point where a very large increase in torque will not make it stall much higher. That is what I think I am seeing with the converter I am talking about. It just reaches this limit with a smaller amount of torque.

Now, as the turbine is allowed to rotate, the phase relationship between the impeller, turbine, and stator is changing. This is when the stator starts to become an energy consumer. At this point, things get really difficult to explain, and even more difficult to describe mathematically. This is where I need some help!
Billy

[GTXMONTE]

Cd you are right, a convertor never totally locks(not a race one anyway) but we are just calling the max stall point "lock" in this discussion. Okay, here we go. Billy, you are right in your turbine and impeller facts, about these two being the parts that produce the stall. The main purpose of the stator is to try and "lock" the convertor up after that stall point has been reached. The stator forces the fluid in the opposite direction in an attempt to have all components working as one as we go down the track. Now we all know that a convertor has a percentage of slippage in high gear, but a properly machined stator will make that percentage small. The pitch on a stator is generally determined by how thick it is. The diameter is not critical. When you machine a stator thinner, you have decreased the length of fluid flow, therefore killing the velocity, which in turn is attempting to "lock" the convertor. The fine line that convertor builders walk is the one that allows desired "stall" before the stator takes over, or it takes over too late and allows the convertor to slip in high gear. Now as far as mathematical numbers on this relationship, I have no idea where you will find those.

Monte Smith

[Billydelrio]

GTX Monte, I must have it pictured bass ackwards. I have it in my mind that the stator is locked and providing "help" up to and slightly above stall speed. After that, it is mostly in the way and is on the sprag so it can freewheel because the turbine is feeding it fluid from an angle greater than 90 degrees (from behind). I am thinking that this "in the way" is causing high rpm power consumption.
Billy

[djswwg]

If you want a concise and easy to understand explanation of how a tork converter works, check your B&M catalog; it's in there. By the way, all of your explanations are correct, just not totally complete. It's true what a couple of you guys have posted, "you understand it, but it's hard to explain"....djs

[GTXMONTE]

Billy, lots of race convertors are spragless, so the stator could not freewheel at higher rpms. The reason I know a little(very little) about stators is because I went through all this with my convertor builder. With the stall I had, my convertors had more slippage than I wanted in high gear, to make them tighter Kenny had to build custom stators to get what we needed.

Monte Smith

[Billydelrio]

I would think that a spragless converter would work up to a particular rpm and and not work worth a squat beyond that.
On the other hand, a statorless converter would not have any torque multiplication but would still work at higher a rpm. This would make it a fluid coupling. The old "J" converter had a stator design that limited torque multiplication, I believe, to limit wheel spin on Hemi and other tork monsters.

GTXMONTE, you said that your converter builder had to try different stators to control slippage. It is the design of the different stators that I would like to hear about, provided that Kenny provided you with that information.
Billy

[Billydelrio]

I have this idea that the stator is to a converter as a camshaft is to an engine. We all compare, predict and then choose or design a cam profile for our application. Why can't we do the same for a torque converter stator. After all, we don't change engines as often as we change cams.
The diameter is comparable to the bore and stroke (cubic inches). The impeller and turbine pitch is comparable valve and port characteristics. Then the stator is comparable to the camshaft.
My point is: all the cam makers list the profiles of the cams that they have made with "NUMBER CHARACTERISTICS." Why do the converter makers not do the same. I know that most people will not have the slightest idea what the "numbers" mean, but is that not true for camshafts also.

I plan to build my own converter one day. But for now, I have no choice but to pay $1000 for one. It just seems to me that I should not have to reinvent the stator when so many people out there should know what I want to know. When I say reinvent the stator, I mean have numerical data for stator profiles.

More to come later!
Billy

[Warren J]

Stop thinking just about high stall. A torque converter works the same whether its high stall or not. What drives the rear(or front) wheels is a fluid coupling. Unless you have a LOCK UP CONVERTER,you do not lock up. Refer to it as coupling. A lock up converter uses a mechanical clutch inside the converter to make the converter not slip a 1 to 1 lock. If the converter clutch did not disengage when you came to a stop the motor would die. A regular converter uses fluid to couple so it slips, all the time. Stall speed is coupling. The best converters slip anywhere fron 3-6%. A torque converter will multiply torque from the end of the crank anywhere from 1.6-2.3 times to the rear end. Lets say you had an engine that made max hp at 8000rpm and max torque at 5500rpm.What stall speed converter would you want? Some say just above max torque and some say half way between max hp and max torque. If you had a converter that only stalled to say 5000 rpm's, on the 1-2 or 2-3 shift the car would not accelerate as well as a 55000 stall. You would be out of your torque peak. A converter can slip to much. It will not reach coupling so it won't be effecient. A street converter still works the same way. On street cars you do not need the brutal acceleration so they don't slip up to max torque.

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[GTXMONTE]

My race convertors are spragless and work quite well. Mine flashes to about 6000, I shift at 8800, go through the traps at 9000 and according to my figures slippage is about 3%, pretty damn good convertor. All I can tell you about the custom stator is that he could not get the pitch angle he wanted with what was available within the thickness area we had to work with. So he built a custom steel stator that had the vane angle and height that he wanted. Now where you are going to get the info about how he wanted the stator....well, I guess you'll have to take that up with someone who builds convertors. I can tell you this, you take the stator I had and install it in a convertor with a diff vane angle on the turbine or impeller or both, and that convertor would be nothing like mine. There are too many variables to be able to "pick" a stator out of a book as you are theorizing.

Monte Smith

[Runner1971]

has anyone had any experiance with the neil chance bolt togethers, how do you change your stall speed on those? acording to chance its suposed to be pretty easy?????

[djswwg]

Like runner1971, I'd like to know about the neil chance converters too.

[Billydelrio]

Yea, I would like to open up a Chance Converter and see what makes it tick also. Seems to me that the stator is the only thing that would be easy to change.

Warren J: The only reason that I am talking about higher stall converters is my need for one.

GTXMONTE: Wow, I am surprised that a fixed stator would allow you to turn such a range of rpms and not turn into a furnace.

Here is something else that I think! The angular velocity of any diameter impeller is the same at a given rpm. The larger the diameter, however, the higher the centripital acceleration will be on the fluid by the impeller. This means the larger diameter converter will reach static pressure at rpms much lower than a samller converter. This is why the higher stall units are much smaller than stock units. If one tries to make a larger unit stall higher by modifying the impeller and turbine characteristics, the unit will loose efficiency (more slippage). This is why I have been looking mainly at stator designs.

GTXMONTE: I would think that a fixed stator design would work great in a tractor pull type where a certain rpm is maintained to produce full torque. Looks like I have a lot to learn!!!

This has been a nice conversation.
Billy

[Billydelrio]

WARREN J: I read your post a second time and found something new. You said, "stall speed is coupling." Well, let us discuss that.

I do not consider stall speed and coupling speed the same. Stall speed is the rpm at which the engine can't force the impeller to produce any more pressure on the turbine (when the turbine is held). Coupling speed is harder to define as the turbine is now in motion and transferring torque into the transmission. I consider coupling speed the rpm at which the turbine is a "middle man" and is allowing torque from the impeller to pass on to the transmission. This coupling can happen at any speed, depending upon torque demands from the transmission and torque signals from the engine. Of course, even during "coupling" there will be slippage. Example: The car is at idle in gear. When the foot is on the brake, the converter is stalled. When the foot is lifted, the car starts to move as the turbine is trying to match rpm with the impeller (coupling).

Does that sound reasonable?
Billy

[Warren J]

If you have a converter that stalls at 5500rpm at what rpm do you say you have reached coupling? If you were coupled at idle you would be at a almost 1-1 couple, no acc at all. I guess I would like you to define coupling, maybe I'm wrong.

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