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Old 11-18-2002, 10:13 AM   #1
live311
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Default A thought on Subaru's 4EAT AWD (non-WRX)

While driving in the pouring rain all weekend at highway speeds, I was wondering if the AWD would be able to help if I suddenly lost control at 60 mph. I know that the torque split is 90/10 in 3rd gear and above, and the car would need to downshift into 2nd or 1st to get to 50/50. If I suddenly did start to slide, the car would handle more like a FWD econobox until it downshifted, and by the time it did it would probably be too late to power out of the slide. Or let's say that I'm on the track and I need to power out of a nice sweeping left-hander at 70 mph. It would basically handle like a Civic unless it downshifted, and it's possible that the sudden increase in torque could cause a loss in control. So my question is, is the non-VTD AWD system used by the 4EAT model Subaru's of any use outside of crawling up slippery hills or doing scoobynuts in an empty parking lot? Does that 90/10 torque split at cruising speeds make much of a difference in handling and control (as opposed to true FWD)? Could anyone offer any driving tips to make the most of this AWD system in everyday situations? Or is there any miracle/frankenstein mod that could change the torque split (doubt it)? Any comments from expert track racers or transmission techs would be especially appreciated.
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Old 11-18-2002, 11:42 AM   #2
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I could be wrong, but even at cruising speed, the tourque split is 90/10 normally, but the center diff can still transfer power to the rear wheels without the transmission having to downshift. Besides, if you go into a spin, you want power at the front wheels, so you can use the engine power to pull yourself back to the direction you have the wheels pointing.
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Old 11-18-2002, 12:14 PM   #3
pdlindor
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I think it's important to remember that the torque split is not a hard-locked thing. The torque split can and will change based on detected slippage...IIRC even the non-VTD auto has some logic to attempt to detect these situations as they happen and pre-emptively shift power accordingly.

~Paul
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Old 11-18-2002, 02:56 PM   #4
live311
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Quote:
Originally posted by pdlindor
I think it's important to remember that the torque split is not a hard-locked thing. The torque split can and will change based on detected slippage...IIRC even the non-VTD auto has some logic to attempt to detect these situations as they happen and pre-emptively shift power accordingly.
Is this true? I thought that the only possible power distributions were 90/10 and 50/50, and that it could only do 50/50 in 1st or 2nd gear. This doesn't sound like the active system that Subaru stakes its reputation and sales on. If you can verify your claim that the car can split 50/50 or even vary the split to maximize traction in any gear then my question will be pretty much answered.
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Old 11-18-2002, 03:26 PM   #5
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The AWD system Subaru detects wheel slippage and adjusts the power split as necessary. I'm fairly positive that it can transfer power regardless of the gear you are in.
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Old 11-18-2002, 03:39 PM   #6
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When all of the wheels have traction, then the torque will be split like you said, but if there is slippage, then torque will be sent from the wheels that slip to the wheels that grip. The power split is not a locked in percentage, but a variable percentage depending on transmission gear and wheel slippage.
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Old 11-18-2002, 03:54 PM   #7
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Quote:
Originally posted by HondaH8er
When all of the wheels have traction, then the torque will be split like you said, but if there is slippage, then torque will be sent from the wheels that slip to the wheels that grip. The power split is not a locked in percentage, but a variable percentage depending on transmission gear and wheel slippage.
Keep in mind that without a front and/or rear LSD, the power transfer is simply an adjustment of ratio between front and rear.

live311, I'm not sure if I could verify this to your satisfaction, but I have heard from a litany of sources that the torque split can and will vary based on detected slippage. Now, in 1st gear this might not be true (I think that is a locked 50/50), but for the others, I believe that the ratios are actively changing.

~Paul
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