I wonder if one can affect/modify either the torque multiplication factor or the stall speed of an automatic tranny by different ATF. It seems a thinner oil might increase the stall speed, but may also increase overall slippage and heat generation. Not sure if torque multiplication would be affected.
ATF, Torque Multiplication and Stall Speed
- Thread starter TallPaul
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I'd think so Paul, but I'd also guess you'd have to make a pretty big viscosity change to make a noticeable difference. I know of people who use synthetic grade 30 engine oil in automatics. It definitely effects the way they shift, noticeably firmer, and they deliver higher line pressure. Might knock a hundred rpm off the stall speed, I guess. Any change in stall speed would certainly effect torque multiplication but I'm not sure a hundred rpm would make much of a difference.
My thinking is to consider extremes. Very heavy oil would result in poor torque multiplication, so thinner should be best for the most torque multiplication.
But your right foot controls the TM far more than a tiny viscosity difference. Hit it hard when starting out, and you get maximum TM from the converter.
But your right foot controls the TM far more than a tiny viscosity difference. Hit it hard when starting out, and you get maximum TM from the converter.
Originally Posted By: mechtech2
Hit it hard when starting out, and you get maximum TM from the converter.
Yep, that's what I do, but I am going to practice how fast I can mash the pedal.
If viscosity makes that much difference we should notice a change from cold start winter to hot engine, but if there is a noticible difference I have never noticed it.
I read that the lower Viscosity for Dex 6 is to help with CAFE. Next they will be watering down the rear end dope to help CAFE. I wonder when they will start running 200 psi aircraft type tires?
Hit it hard when starting out, and you get maximum TM from the converter.
Yep, that's what I do, but I am going to practice how fast I can mash the pedal.
If viscosity makes that much difference we should notice a change from cold start winter to hot engine, but if there is a noticible difference I have never noticed it.
I read that the lower Viscosity for Dex 6 is to help with CAFE. Next they will be watering down the rear end dope to help CAFE. I wonder when they will start running 200 psi aircraft type tires?
Come on, TallPaul... doesn't your torque converter waste a whole lot more energy when it is cold? If so, isn't the biggest culprit the ATF viscosity being too high while it is cold? Sure doesn't help with torque output, it just wastes energy.
Of course, that is not an 8 cSt versus 6 cSt issue, the ATF is probably in the 100-1000 cST neighborhood when freezing cold.
Of course, that is not an 8 cSt versus 6 cSt issue, the ATF is probably in the 100-1000 cST neighborhood when freezing cold.
Also consider that I normally don't give it a lot of pedal when cold, so likely would not notice any difference. But it seems to get a significantly higher stall speed I may need to go to about 4 cSt, but ...
They already water down the rear end, they under fill it. I saw a newer chevy with a tag by the plug that stated full was 30mm or something like the below the plug hole. Same reason the 110 gear oil spec was brought about, to break apart the 90 and 140 range so they could better specify the viscosity.
Thermostatic heat exchanger? On my vic with its thermostat controlled the temp will get to 180 or so, then it stabilizes. Even with a lot of WOT and driving it around like a cop it will stay 180-190. Once climbing a mountain, with the TC unlocked for a long time it got up to 200, though. Dropped to 180 on the other side. That's the reason I have a +2 quart pan ready to go on, for better buffering for such situations.
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MolaKule
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The optimum ATF (theoretically) would have a viscosity of 0 cSt, but one needs some viscosity to provide a fluid film for lubrication/anti-wear prooperties.
I don't think the difference between a 10 cSt and a 6 cSt is going to make much difference in TM or stall, rather the design of the converter makes a big difference.
I don't think the difference between a 10 cSt and a 6 cSt is going to make much difference in TM or stall, rather the design of the converter makes a big difference.
Hmmmm, could be done perhaps if the tranny were (could be) constructed to have a separate system for the torque converter fluid.
You might be able to get your converter restalled or buy one that has been restalled, if you really wanted to change it.. I think the most it can be tweaked is like 3-400RPM though.
Separate system is a nice idea, but it would require a complete reengineering.
Separate system is a nice idea, but it would require a complete reengineering.
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Why would a torque converter waste energy with cold fluid?
More pumping loss.
It's not obvious but a TC is like a pump and motor in one housing. The engine driven side is a hydrodynamic pump and the output side is a turbine (motor).
It's not obvious but a TC is like a pump and motor in one housing. The engine driven side is a hydrodynamic pump and the output side is a turbine (motor).
All converters waste energy with cold or hot fluid due to slippage. That all goes away when they go into lockup mode though. Lockup is the only time a converter is efficient due to the lack of slippage-fluid also runs slightly cooler too as a fringe benefit.
Originally Posted By: mechtech2
My thinking is to consider extremes. Very heavy oil would result in poor torque multiplication, so thinner should be best for the most torque multiplication.
But your right foot controls the TM far more than a tiny viscosity difference. Hit it hard when starting out, and you get maximum TM from the converter.
How does that compare to a brake stall and getting the rpms up to 2k or so?
I've found that by doing a brake stall you are up in the rpm range (off idle) and are already into higher timing tables based on rpm and TPS position.
My V8 Taurus takes forever to actually start to move if just going from idle to an immediate WOT. Almost a full second before I record any mph change. 60' times are 2.2 seconds or higher.
My thinking is to consider extremes. Very heavy oil would result in poor torque multiplication, so thinner should be best for the most torque multiplication.
But your right foot controls the TM far more than a tiny viscosity difference. Hit it hard when starting out, and you get maximum TM from the converter.
How does that compare to a brake stall and getting the rpms up to 2k or so?
I've found that by doing a brake stall you are up in the rpm range (off idle) and are already into higher timing tables based on rpm and TPS position.
My V8 Taurus takes forever to actually start to move if just going from idle to an immediate WOT. Almost a full second before I record any mph change. 60' times are 2.2 seconds or higher.
I'm always amused at the concept of a torque converter having a specific 'stall speed.' Stall speed is dependent upon torque input vs. rpm (and obviously converter design). IOW, a given torque converter installed in a 727 Torqueflight behind a 2-bbl 318 will have a very different stall speed vs. when you take that exact TC (shoot, take the whole transmission) and put it behind a 440 six pack or a 426 hemi, vs. when you put it behind an 8-liter V-10 or Cummins turbo-diesel in a pickup, vs. behind a 2-liter Neon.
I don't recall a variable in the equation I used to use/know for computing stall speed, but that may be simply because the equation was set up with a given ATF viscosity in mind. I'm sure XS650 could post the equation, though (I don't seem to have it any more).
I don't recall a variable in the equation I used to use/know for computing stall speed, but that may be simply because the equation was set up with a given ATF viscosity in mind. I'm sure XS650 could post the equation, though (I don't seem to have it any more).
Stall speed is TC "K factor" times square root of the torque.
Originally Posted By: bulwnkl
I'm always amused at the concept of a torque converter having a specific 'stall speed.' Stall speed is dependent upon torque input vs. rpm (and obviously converter design). IOW, a given torque converter installed in a 727 Torqueflight behind a 2-bbl 318 will have a very different stall speed vs. when you take that exact TC (shoot, take the whole transmission) and put it behind a 440 six pack or a 426 hemi, vs. when you put it behind an 8-liter V-10 or Cummins turbo-diesel in a pickup, vs. behind a 2-liter Neon.
I don't recall a variable in the equation I used to use/know for computing stall speed, but that may be simply because the equation was set up with a given ATF viscosity in mind. I'm sure XS650 could post the equation, though (I don't seem to have it any more).
True. You can imagine how frustrating it is for a TC manufacturer to guess the stall speed when dealing with turbo cars. A small turbo car might stall higher than a higher power large turbo car due to the spool characteristics of the turbos. That's probably the reason I'm on my 5th torque convertor.
I'm always amused at the concept of a torque converter having a specific 'stall speed.' Stall speed is dependent upon torque input vs. rpm (and obviously converter design). IOW, a given torque converter installed in a 727 Torqueflight behind a 2-bbl 318 will have a very different stall speed vs. when you take that exact TC (shoot, take the whole transmission) and put it behind a 440 six pack or a 426 hemi, vs. when you put it behind an 8-liter V-10 or Cummins turbo-diesel in a pickup, vs. behind a 2-liter Neon.
I don't recall a variable in the equation I used to use/know for computing stall speed, but that may be simply because the equation was set up with a given ATF viscosity in mind. I'm sure XS650 could post the equation, though (I don't seem to have it any more).
True. You can imagine how frustrating it is for a TC manufacturer to guess the stall speed when dealing with turbo cars. A small turbo car might stall higher than a higher power large turbo car due to the spool characteristics of the turbos. That's probably the reason I'm on my 5th torque convertor.
MolaKule
Staff member
Here is a well written and accurate article (the exception) from Wikipedia:
http://en.wikipedia.org/wiki/Torque_converter
http://en.wikipedia.org/wiki/Torque_converter
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