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

[oab_au]

Well I wrote this in a thread called.' Can I "turn off" the AWD ' back about Jan this year.

"Yes well when they quote the torque split for the VTD, they seem to put it as 40% 60%, instead of the actual 36/64 that it is. Now I suspect that this was, then applied to the Transfer system, the other way around.

The Transfer system torque split varies with a number of inputs. Selected gear, road speed, and throttle opening. The split is highest with the lowest gear, the lowest speed and the highest throttle opening.

To put this into numbers, when it is in 4th at 30mph/60kph, and you are accelerating hard, the split would be around 60/40, as the road speed rises, the split will reduce to say 75/25. As soon as you lift the foot, the split will reduce to 90/10.
When you are taking off hard in 1st, the split is 50/50, as there is a high chance of wheel spin, so the torque split is increased to max. As the speed rises, the split reduces.

So mate it is hard to state what the standard split would be, just driving down the road. If you are just cruising, it would be 90/10, hit the throttle to overtake, it would go to say 70/30, lift the foot, back to 90/10. It will allways vary to suit the conditions, though it allways needs some drive to the rear, to prevent the rear drive line from shunting. ".

Pretty close to what you have seen. I agree with Beav, 49/51 is not possible.

Harvey.

[Chiketkd]

Originally Posted by oab_au

Well I wrote this in a thread called.' Can I "turn off" the AWD ' back about Jan this year.

"Yes well when they quote the torque split for the VTD, they seem to put it as 40% 60%, instead of the actual 36/64 that it is. Now I suspect that this was, then applied to the Transfer system, the other way around.

The Transfer system torque split varies with a number of inputs. Selected gear, road speed, and throttle opening. The split is highest with the lowest gear, the lowest speed and the highest throttle opening.

To put this into numbers, when it is in 4th at 30mph/60kph, and you are accelerating hard, the split would be around 60/40, as the road speed rises, the split will reduce to say 75/25. As soon as you lift the foot, the split will reduce to 90/10.
When you are taking off hard in 1st, the split is 50/50, as there is a high chance of wheel spin, so the torque split is increased to max. As the speed rises, the split reduces.

So mate it is hard to state what the standard split would be, just driving down the road. If you are just cruising, it would be 90/10, hit the throttle to overtake, it would go to say 70/30, lift the foot, back to 90/10. It will allways vary to suit the conditions, though it allways needs some drive to the rear, to prevent the rear drive line from shunting. ".

Pretty close to what you have seen. I agree with Beav, 49/51 is not possible.

Harvey.

Harv,

I must agree that more than 50% to the rear wheels would be an impossibility based on the design of the awd 4EAT.

In the above info, in MY 'field testing' I never once saw a torque split of 90/10 when cruising along a flat highway at a constant speed. With the shifter in 'D' the torque split always defaulted to 60/40. The harder you accelerated, the split would shift to 50/50; the faster you took a corner, the more the torque would go towards the front wheels on entry at 75/25.

-Chike

[Chiketkd]

Originally Posted by 87f383

awesome info... I don't drive a gloried FWD car anymore... lol

I know what you mean...

The SSM is an amazing device that Subaru developed.

-Chike

[Chiketkd]

Originally Posted by IggDawg

no kidding... this is VERY cool info. and I assume all this is due to the TCU, so the fact that I have (what I assume to be) a legacy transmission, it should still behave the same way? Any idea if this is standard behavior for all MPT 4EATs?

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

[thundering02]

Since it seams like were only talking voltage to a solonoid would it be thereticly possible to change it manually....namely wiring a potetiometer and just "dailing" the tourqe that you want

[Chiketkd]

Originally Posted by thundering02

Since it seams like were only talking voltage to a solonoid would it be thereticly possible to change it manually....namely wiring a potetiometer and just "dailing" the tourqe that you want

This has been done before by people trying to keep the trans in 50/50 mode. However doing this will cause the drivetrain to bind in turns (unless driving on loose gravel or snow). It's only useful when going in a straight line (e.g. drag racing).

I think it was Guard-TL who wired up switches to put his trans in three different modes: regular awd, fwd (more like 90/10 or 95/5) and 4wd (50/50).

-Chike

[Chiketkd]

Originally Posted by SVXRide

Tom,
Remember that we did the same thing with the SSM in my car at the "drag meet" at Mason-Dixon. Of course the TCU was sending the 40% into a "black hole" as the Solenoid C was not functioning at the time...
-Bill (enjoying the start of a new season of autoX - especially with a functioning AWD system!!)

This is a good point you mentioned here Bill. The TCU is sending signals to the Solenoid C to vary torque regardless of whether the solenoid is functioning or not. If the solenoid is inactive, then 100% of your power will go to the rear wheels as the transfer clutch can no longer function.

A properly functioning Solenoid C will basically 'chatter' on & off incessantly to follow the TCU's commands.

-Chike

[SVXRide]

Originally Posted by Chiketkd

This is a good point you mentioned here Bill. The TCU is sending signals to the Solenoid C to vary torque regardless of whether the solenoid is functioning or not. If the solenoid is inactive, then 100% of your power will go to the front wheels as the transfer clutch can no longer function.

A properly functioning Solenoid C will basically 'chatter' on & off incessantly to follow the TCU's commands.

-Chike

Chike,
fixed your post...
-Bill

[TomsSVX]

all this info on the auto got me thinking. What is the split for a 91 4.11 legacy mt? Just curious. If anyone knows, let me know.

Tom

[Chiketkd]

Originally Posted by SVXRide

Chike,
fixed your post...
-Bill

Thanks! I wish that was the case...

-Chike

[Chiketkd]

Originally Posted by tomssvx

all this info on the auto got me thinking. What is the split for a 91 4.11 legacy mt? Just curious. If anyone knows, let me know.

Tom

Someone correct me if I'm wrong, but I've read that the awd Subaru 5MT's use a viscous coupling center diff to vary torque from an pre-set 50/50 split...

-Chike

Originally Posted by Chiketkd

Someone correct me if I'm wrong, but I've read that the awd Subaru 5MT's use a viscous coupling center diff to vary torque from an pre-set 50/50 split...

-Chike

That is what I heard.




Dave

[TomsSVX]

so the mt's are usually 50/50 like the autos are 60/40? just making sure i understand.

Tom

[IggDawg]

non-wrx MTs are 50/50 and any slippage will make that split vary, but the VC diff "tries" to get that 50/50 split back when the VC fluid is stressed and heated. it reacts to any difference in spin between the front and back wheels.

the WRXs are 55/45 IIRC, but react the same way.

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.

[TomsSVX]

ah, gotcha thnx for the valuable info.

Tom