Torque Convertor

sirhk100

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As you can tell by my list of posts in the last day or 2 I'm in transmission land having fun. Okay, through the research I'm finding I've got tons of info but still one dumb question.... On the torque convertor what's the stall rate affect? I've always heard people talking about it but never found out what cnaged as the stall rate varied or went up. Any info would be greatly appreciated. Khris


'99YZ400,
'92 Ford Exploder lifted work in progress,
lifted golf cart
 

Kritter

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I am pretty sure that the stall rate RPM is lowest RPM that the TC will transfer as much power as it can. Any RPM below that it is still spooling up...that's why on drag cars they run a high stall because they can get the RPMs up before they launch and be in there power band. If you get a custom TC made, have it matched to the motor and it will be nice.

Kris
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Chris_Wilson

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I played around with different stall speeds on a class 8. I found the higher stall felt much faster
and really launched hard out of the hole but it also made more heat and I figured it would be
less reliable so I run a lower stall converter now with excellent reliability. If I was doing a
short couse setup I'd go real high with the stall speed, endurance racing go on the low side.
The actual numbers depend on your motor. For me a high stall is 3800-4000, low stall is 2800.
 

BIG_FAT_LOSER

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This may be long winded and of no help but:

To Quote the Summit catalog:

BUILDING THE PROPER ENGINE:
A torque converter reacts to engine torque: the more torque you feed a converter, the better it will perform. For a converter to operate properly, you need to build your engine to make as much low and midrange torque as possible in the same range the converter is rated for.

STALL SPEED:
Nothing about torque converters is more misunderstood than stall speed. Stall speed is directly related to the amount of torque your engine produces-the more torque, the higher stall speed. For example, a converter with a 2,800 to 3,200 rpm rating, might provide approximately 2,800 rpm of stall speed behind a small block V8, but about 5,000 rpm behind a big block making 800-plus ft-lbs. of torque. Without knowing how much torque your engine makes, you cannot know how much stall speed a converter is capable of.
That leads to perhaps the biggest problem people have when buying a converter: stall speed ratings. While most converter manufactures list stall speed ratings, those numbers are very, very general guidelines: true stall speed is impossible to measure due to vehicle variables. the time-honored method of testing a converter's stall speed--holding the brake and reving the engine while in gear--doesn't work, primarily because the tires will spin before you reach the converter's stall rpm.
Most complaints about converters center on a stall speed that is too low. The problem is usually a lack of low-end torque, but there are other variables that can contribute to lower stall speeds, including the following: Low vehicle weight...Small cubic inch engine...very low compression ratio...Tunnel ram-type intake manifold...Large carbuerator throttle bodies..Mechanical secondary carbuerator linkages..Multiple carburetion...Long duration camshafts...Retarted cam timing.

Heat is the biggest enemy of your converter and transmission. Stepping up to a higher stall converter can impose higher loads and create more heat, so proper cooling is essential


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ntsqd

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All a converter is, is two fans facing each other. One is driven by the engine, the other gets driven by whatever fluid they are immersed in. Be that water, oil, or air. There is some other stuff in them, but the intent of it is just to increase the tranmission of power.

Stall speed is the engine speed where the torque converter achieves near one to one coupling. You can determine what your current stall speed is if you can put the trans in direct. It has to be 3rd directly, not just drive. Usually the only way this is possible is if the trans has a manual valve body. Assuming you can do this, lock up the brakes and floor it. The engine will rev up to some rpm and not be able to go any faster. This is your stall speed. The problem with trying this in a non manual valve body is that the trans starts in first which results in torque multiplication. Not what you want.

Drag Racers use a high stall converter for a couple of reasons. Usually their cam is so large that torque down low in the RPM band is non existant. By using a higher stall they can get to engine up where the cam wants to run. By launching at or near peak torque, their 60 ft times improve.

Rock Crawlers used to use stock or even lower than stock stall speeds. With the advent of 'bumping' an obstacle bigger cams and higher stalls are getting more common.

RV's and heavy towers usually use a slightly higher than stock stall speed. The idea here is to get a little more torque multiplication for getting things moving away from a light, but still stall the converter fairly soon so as to keep the heat generation under control.

TS

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-- Bumpersticker seen in Lost Wages
 

sirhk100

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Thanks for the descriptions and info. That's pretty straight forward and makes sense. I'm assuming I can walk into a reputable shop that has experience building auto trannys for off road and they'll be able to ball park the stall speed for my setup right? It sounds like I would want something similar to the RV torque convertor.

Thanks again for the info

Khris

'99YZ400,
'92 Ford Exploder lifted work in progress,
lifted golf cart
 
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