a few questions on torque converters

Z

zeek

Veteran Member
Mar 6, 2004
2,872
somewhere in jersey.
i gota do a report/presentation for auto shop class tommrow on the torque converter eh can any one tell me why torque converters come in differnt sizes and whats the biggest and smallest size they come in thanx in advance im trying to get a good grade
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this is post 100 hehe
 
D

deet

Veteran Member
Apr 1, 2002
1,549
Martinsburg WV usa
Not to sound indifferent or anything but you could write an entire book trying to answer your question. Simply put Torque converters come in different sizes because motors come in different sizes. What a torque convertor does is keep the motor from stalling under load from the tranny. It does this by having two opposing vanes seperated by a viscous fluid. The motor spins one vane which in turn pushes the fluid through the other vane causing it to spin and thus turning the tranny. Now since the motor is not directly coupled to the transmission the vane on the motor side will continue to spin at idle speed while the one on the tranny side remains stationary when you are stopped in drive which is why the motor doesn't stall. Now motors have different stall speeds so you need a torque converter that will match your motors stall speed. For instance if you take the torque converter out of a 4 cylinder vega and install it behind a 350 sbc the drivetrain won't engage until around 2500-3000 rpm. In contrast if you put a torque converter off of a 350 on a 4cylinder vega the motor will stall out and die.

I can't answer your question about biggest and smallest unless I know what drivetrain set up your talking about.

There is way more to tell you but that is the basic theory of it.

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If it's got tits or tires there's gonna be trouble.



[This message has been edited by deet (edited March 24, 2004).]
 
D

deet

Veteran Member
Apr 1, 2002
1,549
Martinsburg WV usa
That's really tough to answer given that there were also lock up converters offered with that tranny. A stock converter should have a stall speed of between 500 and 1000 rpm. It's really complicated to say for certain considering the engine has alot to do with it too. I would dare to say that for every engine/tranny combination that GM made there is also a converter. I don't work in a parts store so I couldn't begin to tell you that. Now the aftermarket has stall converters in the 1500-2000 range,2000-2500, 2500-3000, and so on up to 5000 in increments of 500.

The biggest variant on stall speed is the motor itself. A stock motor can use a low stall speed where as a tire frier will need a high stall speed. Basically the smoother the idle the lower the stall you can run safely. This is because that lumpy idle creates a low vacumm condition which will allow the motor to stall and die easier.

I hope somebody here can give more info if you need it. Im sure there are people here way smarter on this subject than me.

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If it's got tits or tires there's gonna be trouble.

[This message has been edited by deet (edited March 24, 2004).]
 
B

bj's72sc

Veteran Member
Oct 16, 2002
914
Kirkland Wa USA
Geez Deet! All that info and you only got a B! Lol I love it when the knowledge is shared on this board. What a bunch of good people.

Zeek good job on your report! I know little about torque converters so I learned something here too.

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Brian
72 Camaro coupe
http://www.cardomain.com/id/bjs72camaro
69 Firebird convert.
http://www.cardomain.com/id/bjs69firebird
 
T

Transman

Veteran Member
Feb 26, 2004
279
Waterloo, Iowa USA
Okay, here goes...first, a torque converter is a device that couples the engine to the transmission. It has three main parts. The pump, or shell of the converter, which turns at engine speed. The turbine, which is splined to the input shaft of the trans. Lastly the stator, which is the device that separates the modern torque converter from the old "fluid couplings" that had no stator. The physical size of the converter along with the configuratoin of the stator and fin angles in the pump and stator are what determine the torque multiplication and stall speed characteristics of the converter. Generally the smaller the converter the higher the capability it has for stall speed increases. There are two common stators used in most of todays race converters. First is the "C" stator. It is a cast aluminum part in its stock form, and is fine in mild performance applications. It is duplicated in investment-cast steel for race use. The C stator can be machined down to take away some torque multiplication and "hit" from the converter, and when this is done it is then termed a "CCX" stator. These can be either a modified OEM aluminum one, or a modified aftermarket cast steel version. There are two other common stators used in applications that require a softer hit, and they are the A and B stators, and they are also cast aluminum. They have their cut versions also, and are the AXC and BCX. As for fin angle, generally the more positive the fin angle is the "tighter" the converter is, or the lower the stall speed level. You can bend the fins to either a positive or a negative fin angle to vary stall speed. The common range is from 150- to 300 or 325+. Each move of 50 in the fin angle will generally change stall speed about 200 rpms. Thus, if you had a converter with a 100+ fin angle that stalled at say 5000 rpms and then changed to a 150+ fin angle while keeping the same stator you would have a stall speed closer to 4800. If you went down from the 100+ to a 50+ you would have about a 5200 stall speed. Thus, you can build just about any combination of stator and fin angle within reason to get the correct combination of torque multiplication characteristics and stall speed desired. Many good converters will use anti-ballooning plates too. Simply put, they are thick steel plates welded on each side of the converter and they control the tendency of the converter to "balloon" apart under the internal pressure generated. They are a must with a transbrake, or nitrous/blown combinations. Also they are a good addition to any converter IMO. Many companies like BTE are now using investment-cast steel front converter halves instead of adding anti-ballooning plates on the front, and they are much stronger than a plate. Another term you hear is "furnace brazed fins". This simply means that the metal fins in the converter are not just bent in place and held by their tabs, but rather they are brazed to the converter so as to increase the strength as loads are applied to them. There is also another part in the converter called the sprag. It is a one-way clutch. When you mash the gas, the pump speed (shell of the converter) is high compared to the turbine speed (input shaft of the trans). Fluid is fed to the converter through the valve body and front pump to the stator area. Here it circulates around from the pump, through the stator, to the turbine and back around again. As the fluid is forced through the stator, it makes the stator lock in place via the sprag. The number of blades and their angle in the stator are what determine the torque multiplication, as previously mentioned. The fluid is directed at the turbine fins by the stator, and this gives you the multiplication. As the turbine speed (input shaft of trans) catches up to the pump speed (shell of converter, or engine speed) something happens in a sprag-equipped converter. The fluid has less differential on either side of the stator, and then as the converter nears its maximum efficiency point, or stall speed, the fluid wants to begin to flow back through the stator the other direction. In a sprag-equipped converter, the sprag will allow the stator to freewheel now. Some prefer the spragless converters, as they have no sprag to ever fail. But they are less efficient and will never allow as quick of an et or high of a mph as a sprag type converter since the stator is held in place all the time in the spragless converter, and thus it becomes a restriction to fluid flow at higher rpms, when in a sprag type converter it is able to freewheel. That pretty much is a basic look at the how and why of converters. It is easy to see why many times a guy calls up a mailorder place and gets some doofus on the phone who has no idea of the inner workings of a converter. I have raced since the late 70s, and pretty much learned how and why converters work, and what combination works best for a particular situation. The real key is to have realistic goals for your combination, and stick to a plan to have all the parts work in harmony. You can't have a 1000 hp motor and a junkyard converter. Many times I see people overestimate their power and torque levels, and then get the wrong converter. If in doubt, ask around and spend your money once, not twice! If you want to see an exploded view of these components I talked about, go to my site, and on the "hot items" page I have a picture of the inside of a converter. A misconception too is that you need a "custom built" converter. Since you know that there are only so many stator and fin angle combinations possible, you now see how it is nearly impossible to think that you have a combination that is so unique that no one else has ever used it! In fact, if a company is smart, they will stock some of the most common converter combinations on their shelves, and have them ready to ship out immediately. If you need any more info on converters feel free to ask away!

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Oldani Motorsports BTE, TCI and JW dealer
 
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