It tries to transfer half of the torque, but it's limited by the center diff. I don't have hard data on what torque amount they start slipping at, but it's nowhere *near* half.
I have it at 600nm atm. It's a viscous so that is already incredibly tight in practice. Maybe the GT-R viscous center is somehow much tighter than standard viscous units; not impossible. I've considered it but there are many factors which play into it, like launches from a standstill just not having enough grip in any sim to begin with. Probably something to do with low speed physics and lack of longitudinal tire flex.
Just to get an idea:
3.827 x 3.545 x 390 = 5291.01885
50% is 2645.509425. The center can lock 600. 600 / 5291.01885 = 0.11339970939
So you only really get about 1/5 of the transfer request in 1st gear at peak torque. It is mostly RWD. That's why GT-R's can drift in 2nd as well, and they don't just immediately go to 50/50 when the rear lets go. 36.7% is the maximum transfer in 2nd gear at peak torque.
