Trans Fluid Type Effect on Stall/Converter Slippage

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Seanh832
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Trans Fluid Type Effect on Stall/Converter Slippage

Post by Seanh832 » Tue Nov 01, 2016 5:57 am

Currently using Mobile 1 Synthetic in my Turbo350 with a 5000RPM Hughes 8" Converter in a 2600lb car at 700hp. I've heard Tractor fluid works well but will affect stall speed and converter slippage to some degree. Anyone notice a difference in trap speed, 60' E.T., RPM crossing the finish line? If so, Which fluid did you try? What is the viscosity? I'd love to tighten mine up a couple hundred rpm without sending it in for an adjustment.
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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by BOOT » Wed Nov 02, 2016 12:45 pm

Interested as well
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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Seanh832 » Fri Nov 04, 2016 4:34 am

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Seanh832 » Fri Nov 04, 2016 4:38 am

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Brian P » Fri Nov 04, 2016 5:57 pm

Since no one has attempted to explain this, I'll tackle some theory.

The torque converter is a hydrodynamic device. So is an airplane wing, so is a turbine or centrifugal pump. It fundamentally operates based on momentum of moving fliuds - changing direction of moving fluids.

Moving fluids are affected by a relationship between momentum and viscosity which is called the "Reynolds number". Higher viscosity tends to add frictional losses and make the flow more sluggish.

So, yes, higher viscosity fluid could very well affect the "stall speed" to some extent, but it will be at the cost of torque multiplication - basically, it makes the torque converter less like a torque converter and more like a slipping clutch (or fluid clutch - no torque multiplication).

Imagine what would happen if you filled it with thick goo instead of light oil. It'll slow down the action all right - but it also won't function very well at all.

Now, maybe, that lower stall speed and less torque multiplication might be what you are looking for, and if so, perhaps it's a valid "on the spot" course of action. But really it's a "racetrack fix" - a cheap substitute for altering the blade angles and flow directions - but it's something that can be done on the spot at the track instead of tearing things apart and changing stuff.

Relying on the viscosity as a tuning element will cause it to become more temperature-dependent - since the absolute viscosity of typical oils is strongly dependent on temperature. I would think that this is a bug, not a feature. The hotter the transmission gets, the closer it will work to how it's supposed to instead of how it works with your thicker-oil quick-fix in place.

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Seanh832 » Sat Nov 05, 2016 5:54 am

Brian P did you read any of the replies in the 2 links i posted? Sounds like many high horsepower cars run John Deere Hy-Gard in their Automatics with great success. Less wear on hard parts, not burning fluid, less friction material in the pan, less clutch slippage, firmer shifts, handles heat much better than ATF, higher flash point (227 vs 180 Celsius), pulls harder in high gear, consistent ET's. Can affect stall speed 2-300rpm IF a higher viscosity is used. At 100 degrees Celsius Dexron viscosity is 7.5 while Hygard is 9.4. Not much difference at temp.
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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Brian P » Sat Nov 05, 2016 9:42 am

Yes, I looked at them. No argument from me concerning the lubrication qualities of the fluids, I can't comment on that. ATF has multiple jobs to do.

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by pdq67 » Tue Nov 08, 2016 6:42 pm

Brian P wrote:Since no one has attempted to explain this, I'll tackle some theory.

The torque converter is a hydrodynamic device. So is an airplane wing, so is a turbine or centrifugal pump. It fundamentally operates based on momentum of moving fliuds - changing direction of moving fluids.

Moving fluids are affected by a relationship between momentum and viscosity which is called the "Reynolds number". Higher viscosity tends to add frictional losses and make the flow more sluggish.

So, yes, higher viscosity fluid could very well affect the "stall speed" to some extent, but it will be at the cost of torque multiplication - basically, it makes the torque converter less like a torque converter and more like a slipping clutch (or fluid clutch - no torque multiplication).

Imagine what would happen if you filled it with thick goo instead of light oil. It'll slow down the action all right - but it also won't function very well at all.

Now, maybe, that lower stall speed and less torque multiplication might be what you are looking for, and if so, perhaps it's a valid "on the spot" course of action. But really it's a "racetrack fix" - a cheap substitute for altering the blade angles and flow directions - but it's something that can be done on the spot at the track instead of tearing things apart and changing stuff.

Relying on the viscosity as a tuning element will cause it to become more temperature-dependent - since the absolute viscosity of typical oils is strongly dependent on temperature. I would think that this is a bug, not a feature. The hotter the transmission gets, the closer it will work to how it's supposed to instead of how it works with your thicker-oil quick-fix in place.
Not a torque converter, but rather a torque mover if you will.

I think AMC used really thick/viscous silicone in their 4WD front/rear drive, "splitter", behind or beside the transmission in their little 4WD Spirit and Concord, ("Hornet" type), cars way back when. I think the, "splitter", was made with two parallel shafts with closely spaced discs on each shaft that intertwined between each other, like two "combs" whose teeth messed together while revolving and the, "goo/silicone", flowed between them and produced the coupling effect.

Please check me here though??

pdq67

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Brian P » Tue Nov 08, 2016 7:43 pm

I'm pretty sure that's accurate. The viscous-coupling type connections were used on other vehicles as well.

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by peejay » Wed Nov 09, 2016 7:07 am

Viscous couplers and viscous limited-slip diffs were used in almost all of the AWD cars of the 80s and 90s, many of the Japanese RWD cars of the 90s and later, and can still be found in cheaper AWD setups where they don't want the expense of active control.

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Re: Trans Fluid Type Effect on Stall/Converter Slippage

Post by Pro Built Automatics » Sun Jan 29, 2017 4:43 am

"Brian P did you read any of the replies in the 2 links i posted? Sounds like many high horsepower cars run John Deere Hy-Gard in their Automatics with great success. Less wear on hard parts, not burning fluid, less friction material in the pan, less clutch slippage, firmer shifts, handles heat much better than ATF, higher flash point (227 vs 180 Celsius), pulls harder in high gear, consistent ET's. Can affect stall speed 2-300rpm IF a higher viscosity is used. At 100 degrees Celsius Dexron viscosity is 7.5 while Hygard is 9.4. Not much difference at temp."
I agree with this as I have worked with others over the years and got very similar results. One of the oils we used was 11 viscosity at 100 degrees Celsius.

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