The Great AWD Torque Split Debate: 90/10 vs 60/40

[Earthworm]

The WRX 5MT in mine has to be 50/50. The AWD doesn't behave anywhere near the same as the 4EAT it replaced. It behaves exactly like my Justy when I lock it into 4WD. (Except for the binding in the corners)

[Chiketkd]

Originally Posted by IggDawg

aside - the AWD system in an auto is arguably "better" since it reacts to the changes in conditions so much faster (electronic sensors vs. heating up a fluid). When a friend of mine took his auto WRX to the Tim O'Neil winter driving school, Tim commented on how much better the auto AWD system felt than the manual.

That's what I've heard as well. The electronic awd system in the auto trans shifts torque much quicker and before any traction loss occurs. Changes in torque split can happen as a result of steering input, braking, gradient of road, etc.

In the 5MT viscous coupling awd, a change in torque split only occurs when there's a loss of traction.

This is one reason why it's next to impossible to get an awd 4EAT stuck in snow, sand, mud, etc., but it's much easier with a 5MT...

Remember this pic:



-Chike

[Ron Mummert]

It's good to see Chike, Beav, Harvey & others giving 110% to this topic.

Ron. (counting toes).

[LarryIII]

Chicke,

Thanks for conducting this experiment and posting this information.

[MPtyza]

Originally Posted by Chiketkd

Correct. The TCU part # for the SVX 4EAT, is different than the one used in the Impreza & Legacy cars of similar model years.

I even bought an awd '93 Legacy TCU just to experiment and noticed a sharp difference in the way it controlled my car. Front wheel spin was definitely easier to come by...

Subaru basically developed a specific TCU for the SVX with a greater emphasis towards performance driving...

-Chike

Hmm, that gets me thinking. I've got a '91 Legacy Turbo. Since you swapped a Legacy TCU into an SVX, would the opposite be possible? Like could I get the 60/40 split in my Legacy if I swapped in the AWD SVX TCU do you think?

Sorry to hijack your thead a little, but that question is burning a hole in my head right now

[Chiketkd]

Originally Posted by LarryIII

Chicke,

Thanks for conducting this experiment and posting this information.

You're welcome Larry. I just didn't get the 'feeling' out cars had a 90/10 torque split as the front tires didn't spin during hard launches (either all four spun, or none at all).

Hopefully, this'll put one myth to rest. The Subaru Select Monitor did provide very compelling evidence - which was backed up on different occassions in different cars by Green_eyed_lady, SVXRide and SVXfiles.

-Chike

[Chiketkd]

Originally Posted by MKP

Hmm, that gets me thinking. I've got a '91 Legacy Turbo. Since you swapped a Legacy TCU into an SVX, would the opposite be possible? Like could I get the 60/40 split in my Legacy if I swapped in the AWD SVX TCU do you think?

Sorry to hijack your thead a little, but that question is burning a hole in my head right now

It may work, but then again it may not. The older Legacys didn't use an electronic speed sensor and the TCU didn't send the ECU a signal to reduce torque on the 1-2 and 2-3 shifts.

-Chike

[IggDawg]

more interesting info... I didn;t know there was no torque cut signal on 3-4... maybe this is why the 3-4 shift seems laggier than the others.

I need another shift kit =D. I miss the hard shifts.

[svxistentialist]

Originally Posted by Chiketkd

You're welcome Larry. I just didn't get the 'feeling' out cars had a 90/10 torque split as the front tires didn't spin during hard launches (either all four spun, or none at all).

Hopefully, this'll put one myth to rest. The Subaru Select Monitor did provide very compelling evidence - which was backed up on different occassions in different cars by Green_eyed_lady, SVXRide and SVXfiles.

-Chike

Thanks Chike.

Good solid measured information.

It would be interesting to get the same information on my JDM and UK SVX trannies, and also on my Legacy twin turbo with 4EAT.

Where did you get the SSM, might I ask? Can one be bought for reasonable money? My brother has a JDM Forester Turbo, which is pretty quick. All our cars OBD I. We are discussing getting a select monitor.

Can you help?

Joe

[And I promise to post up the Euro and JDM torque split figures when I get it ]

[n00b on demand]

So if the split is really 60/40 then why have people all this time thought it was 90/10? AWD is so awesome

[oab_au]

I don't know about dispelling a myth, as creating a monster

It does not matter what number is given to it, the fact remains that the torque split is constantly varying to suit the conditions. The select monitor, really shows the % duty cycle, that is sent to the C solenoid, and this varies from 5%, clutch off to 95% clutch on. You can hear this, by turning the ignition on, don't start the motor, select D,and just move the accelerator from closed to open, you can hear the solenoid buzzing louder as the pedal is pushed down.

The pressure is increased, the more the throttle is opened, and the lower the gear. This is to prevent the front wheels from spinning, due to the higher torque that is applied in these conditions. Once the torque is reduced in the higher gears, and the throttle opening is reduced as the speed rises, the clutch pressure is reduced. It doesn't just stay at the same torque split, all the time.

The only 4eat that has a fixed torque split, is the VTD, at 36% front 64% rear. This split is due to the differential leverage of the gears in the compound planetary diff. This trans runs this torque split all the time, only applying the Limited slip clutch, under the same conditions of starting and hard acceleration, or wheel spin.

The main difference is in hard acceleration and cornering. As Chike has noted in the Transfer system, the torque split is reduced, when turning into corners, and increased when exiting the corner. This is because the split has to be reduced to allow for the difference in front/rear wheel speed, then increased when this difference is reduced, as the same clutch can't apply full torque to the rear wheels, and allow slip for cornering at the same time.

I have found this in driving my Liberty with the Transfer system. Stick the foot down coming into a corner, and it dies a bit till its half way through, then away it goes. The VTD SVX does not do this, just line up the corner, plant the foot, and it just accelerates through the corner, no lag, no under steer

Some other points that I see. All 4eats send a torque reduction signal on all changes. They all use electronic sensing to check for wheel spin. Road grade doesn't affect the split. The TCU for the different 4eats are tailored to suit the car, so they will be different, but interchangeable.


Harvey.

[TomsSVX]

geeze you are a wealth of knowledge on subarus. Will you come live in my garage? i have some moving blankets and a toilet across the hall. I will feed u once and a while. Mostly you will just tell me everything about my car all the time so there is no guessing.

Tom

[Chiketkd]

Originally Posted by svxistentialist

Thanks Chike.

Good solid measured information.

It would be interesting to get the same information on my JDM and UK SVX trannies, and also on my Legacy twin turbo with 4EAT.

Where did you get the SSM, might I ask? Can one be bought for reasonable money? My brother has a JDM Forester Turbo, which is pretty quick. All our cars OBD I. We are discussing getting a select monitor.

Can you help?

Joe

[And I promise to post up the Euro and JDM torque split figures when I get it ]

No prob Joe. I don't own a Subaru Select Monitor - Svxfiles does. He used to be a salesman at a Subaru dealership for many years. Not sure how one can be acquired either. These monitors weren't available to the general public, only authorized Subaru dealerships could purchase them (to the best of my knowledge).

-Chike

[TomsSVX]

Originally Posted by Chiketkd

This is one reason why it's next to impossible to get an awd 4EAT stuck in snow, sand, mud, etc., but it's much easier with a 5MT...

Remember this pic:



-Chike

No, This is why you dont take a subaru on the beach. In sand there are two things u need, air downed tires and clearance, which is hard to do with any car unless you are Jesse. That imprezza is sunk to the frame because they lacked clearance not traction from all fours. Not trying to shoot you down at all just saying, I live on the beach and have seen many auto and mt subaru shoobies get stuck. I usually just point and laugh then drive away in my suby.

Tom

[Chiketkd]

Originally Posted by oab_au

I don't know about dispelling a myth, as creating a monster

It does not matter what number is given to it, the fact remains that the torque split is constantly varying to suit the conditions. The select monitor, really shows the % duty cycle, that is sent to the C solenoid, and this varies from 5%, clutch off to 95% clutch on. You can hear this, by turning the ignition on, don't start the motor, select D,and just move the accelerator from closed to open, you can hear the solenoid buzzing louder as the pedal is pushed down.

The pressure is increased, the more the throttle is opened, and the lower the gear. This is to prevent the front wheels from spinning, due to the higher torque that is applied in these conditions. Once the torque is reduced in the higher gears, and the throttle opening is reduced as the speed rises, the clutch pressure is reduced. It doesn't just stay at the same torque split, all the time.

The only 4eat that has a fixed torque split, is the VTD, at 36% front 64% rear. This split is due to the differential leverage of the gears in the compound planetary diff. This trans runs this torque split all the time, only applying the Limited slip clutch, under the same conditions of starting and hard acceleration, or wheel spin.

The main difference is in hard acceleration and cornering. As Chike has noted in the Transfer system, the torque split is reduced, when turning into corners, and increased when exiting the corner. This is because the split has to be reduced to allow for the difference in front/rear wheel speed, then increased when this difference is reduced, as the same clutch can't apply full torque to the rear wheels, and allow slip for cornering at the same time.

I have found this in driving my Liberty with the Transfer system. Stick the foot down coming into a corner, and it dies a bit till its half way through, then away it goes. The VTD SVX does not do this, just line up the corner, plant the foot, and it just accelerates through the corner, no lag, no under steer

Some other points that I see. All 4eats send a torque reduction signal on all changes. They all use electronic sensing to check for wheel spin. Road grade doesn't affect the split. The TCU for the different 4eats are tailored to suit the car, so they will be different, but interchangeable.


Harvey.

Not creating any monsters here Harv, as my results were backed up by the Subaru Select Monitor and three other members who got the same results.

Never once during my 'field test' did I see a torque split of 90/10. The torque seemed to level out to 60/40 when going in straight line on a flat road after the torque converter locked up. This was also the torque value that displayed on the monitor before we pulled off and put the slector in 'D', '3' and '2'.

I agree that the torque split changes constantly, but it's only when there's a change in the steering, braking, acceleration, etc. I noticed a chnage in split when we went up a steeper gradient, but the road may not have been straight, and this could have been due to changes in steering input.

When I plugged te '93 awd Legacy TCU into my car, the 1-2 and 2-3 shifts definitely DID NOT have any torque reduction.

I did my homework, these were my results.

-Chike