4eat Torque Split

[Subtle]

Anything written by Subaru that I've read seems incomplete.

They mention that the TCU upon acceleration directs more of the torque to the rear. Unlike the lsd it doesn't wait for wheel spin to change.

I cant find out what the split is. Although one of the guys at Rocket Rally mentioned the that feature only worked on first and second gears.

This I like, but with much more performance out of the vf34 it would be nice to have a 35/65 front to back split. If it's good for the STI it's good for me.

On hard acceleration there is too much torque going to the front. Maybe it's 45/55 split.

Any ideas about how to modulate the clutch pack to get the right split

[Splinter]

I cant give you any numbers, but I can tell you that when I was rallyXing with the 4eat, it was digging in something fierce with the front wheels on launches.

Back wheels didnt start trying until I was actually moving

Also, to the best of my knowledge, the construction of the 4EAT doesnt allow for more than 50% of the torque to the rear. I say this because 100% duty cycle on the solenoid gives you 100/0 front/rear, and 0% duty cycle gives you a 50/50 split.

[bmxkelowna]

as far as i know its
90/10 (f/r) in "D" and "3"
50/50 (f/r) in "2" and "1"
unless its my trany then its just gay

[Subtle]

Thanks for the response, but I thought I posted this under the Drivetrain heading.

I still think it should be posted there.

Actually, when I think about it the OEM set up makes sense, but not with higher performance.

[vrg3]

Splinter is correct about the automatic AWD system's construction.

The front is attached to the transmission's output shaft, just like with FWD. You cannot disconnect the front wheels from the transmission's output.

The rear is attached to the transmission's output through the multiplate transfer clutch. The TCU can vary the MPT clutch's lockup from being completely engaged to being completely disengaged.

I don't fully understand how exactly this translates into torque splits, especially when wheels start to slip, but it seems pretty clear that under hard acceleration the best you can do is locking the MPT clutch fully (what some might call a "50/50 torque split"), except that you have to be going in a straight line.

If the TCU isn't doing this how you want it to, wire a normally-closed pushbutton switch in series with Duty Solenoid C, and wire a suitable resistor (a 470-ohm 2-watt resistor maybe) in parallel with the pushbutton-solenoid pair. Then you can push the button to force full lockup.

[Subtle]

Thanks guys---reality has ruined a great concept

Got to go now---will have some questions

Later

[Splinter]

Splinter is correct about the automatic AWD system's construction.

woo! Thats like, the 10th time Ive been right about something

Maybe Im becoming a real live subaru guy

[bmxkelowna]

If the TCU isn't doing this how you want it to, wire a normally-closed pushbutton switch in series with Duty Solenoid C, and wire a suitable resistor (a 470-ohm 2-watt resistor maybe) in parallel with the pushbutton-solenoid pair. Then you can push the button to force full lockup.

here is a write up on how to do this
http://www.ultimatesubaru.net/forum/sho ... hp?t=50264

[Legacy777]

Only other comment to what has already been said is that the literature I've read mentions that the TCU varies the duty % to the duty c solenoid depending on various other inputs to the TCU, TPS, vehicle speed, engine rpm, etc.

I can't tell you what percentage happens when. The only way to do that is to tie into the duty C output from the TCU and log the PWM signal along with other signals and analyze the data.

[Subtle]

From what is posted above, the most to the rear is 50 %.

The main interest in the split was to find out how to get it to 65 % at the rear.

The STI must have some kind of a clutch pack in order to dial on the 65 split.

Any comments

[Manarius]

STi's have DCCD to control tranny bias.

[THAWA]

Negative. DCCD does not control torque split.

It has a planetary gearset which sets up the distribution.

[Manarius]

Negative. DCCD does not control torque split.

It has a planetary gearset which sets up the distribution.

I stand corrected

[head2wind]

so this is a noob question but one that is nagging me a bit. If the 4eat has a fixed input to the front diff, is the 5mT the same or does it have a planetary/clutch system that would allow greater than 50/50 split

[All_talk]

so this is a noob question but one that is nagging me a bit. If the 4eat has a fixed input to the front diff, is the 5mT the same or does it have a planetary/clutch system that would allow greater than 50/50 split

The 5MT is not the same, its has a gear diff to split the front/rear drive with a viscous limited slip clutch pack across it... It is a true VLSD diff. And all but the WRX/STi (RS?) 5MTs have 1:1 transfer gears with matching front and rear final drive ratios, so as long as no wheels are slipping, all 4 wheels will get the same torque load. Once a wheel dose start to spin the center VLSD will shift the torque balance tword the axle with more traction.

True the 4EAT can react quicker and more positive (maybe to positive somethimes) but the balance and smooth progressive engagment of the 5MT gives a completely controlled and predictable feel to the car... truly a brilliant bit of engineering.

Gary

[Subtle]

In initiating this thread a month ago, the plus is the AWD lock up.

Thanks again.

[Redlined]

here is a write up on how to do this
http://www.ultimatesubaru.net/forum/sho ... hp?t=50264

Hmmm this write up bothers me and id rather discuss it here among people I know and trust than with people, that are mechanical/electrical morons for all I know.

He "chops" the Pin11 Wire, wich he describes as "solonoid", and runs his Toggle to it. I assume this wire has a function, E.G. Pushes the car into 50/50 split when required. By "chopping" the wire instead of splicing to it. wont this stop the vehicle from switching to 50/50 when required FORCING the driver to do it manually? (perhaps a bit challenging when you find yourself romping through the snow on the wrong side of the road comming up on a corner.)

[free5ty1e]

If he's recommending to disconnect the ECU from the solenoid and just control it with the manual switch then yes, that's a manual control only setup. You could wire up a switch before that switch, either connecting or disconnecting the ECU to the manual control switch, thereby giving you two switches: Automatic Control / Manual Override, and Half Power To Rear / No Power To Rear.

Not sure whether or not the No Power To Rear setting would be good to use, but that's what it'd do.

Edit: just read his writeup, not much detail there.... I believe that with a double-pole switch like he has allows for more than one connection to change with the switch throw. I'm not sure from the writeup but he could have set this up to have a single switch either allow the ECU to control the solenoid, or to force it into the 50/50 split.

[free5ty1e]

You know, with the right IC (a voltage-to-PWM converter), you could put a knob on your dash that would allow you to adjust your distribution from 100 front / 0 rear to 50 front / 50 rear... not quite a DCCD but kinda-sorta (in a roundabout kinda way).

I'd still rather have a 5MT.

Edit: (I can make one of these pretty easily.... should I?)