AFAIK there is no way to change the torque split on our centre diff. unless your lucky enough to find an xtrak box / drive shafts and hubs / struts and have v.deep pockets.

The split is not controlled by gearing but by viscous. I suppose it could be possible to change the viscosity of the fluid in the dif but i have no idea if this will actually change anything to do with the ratio and the unit is sealed.

From all the info I can find, which is next to nie, The Cusco 35/65 diff replaces the open centre diff in the gearbox with a planetry gear arrangement.

Due to the fact that standard evos torque is controlled either via the viscous coupling or the ACD (this is the limited slip part of the centre diff), torque split cannot be controlled front to rear as standard, as we all know. (much like a standard front or rear lsd, the LSD cannot set one wheel to have a 75/25 torque split at all times, it just controls the amount of slip, the more one wheel slips, the more the diff becomes closer to locked) Which is exactly what the ACD does, control slip, it can be locked, or pretty much open (if ACD) it can't choose to make more torque to the front or rear, its simply not in its design, and I can show you.

For the Cusco tarmac diff to work, a special planetry diff replaces the open centre diff, and as this diff now controls the torque split, the ACD/VCU needs to be removed (replaced), otherwise, they are simply going to try and override the 35/65 torque split.

I have heard that the Cusco diff is effectively an open diff, as it does not use clutch packs etc to control torque split, as this would make it a 50/50 "limited slip diff" much like any other LSD, which makes sense, but it does control the ratio of torque - torque split. (Any normal 50/50 centre LSD will have clutch packs, much like a normal LSD, its the gear design that alows for a 65/35 torque split)

As for the GSC 60/40 diff, I believe they use a spool to replace the VCU, but not a locked spool, an open spool. The VCU/ACD is the carrier for the center diff, without it the diff has only one bearing supporting it, and would flop around like an old mans weenie. But again, this seems to be a planetary diff, driving internal parts at differend speeds to induce a torque split (not geared output ratios)

Its a bit confusing, but with a decent driveline diagram, and some explanation I could probably help.

The Cusco Diffs are only stated for evos up to evo 6, as this was the last of the VCU'd cars - apart from some of the USDM evo's, therefor it the 6/7 centre diff is the same, you can use it in your 7, but removing some of the clutch plates from the ACD, or disengaging the pump to render the ACD inoperative.

PM me on the Evo Oz site (lostinthewoods) and I'll send you my number, give me a call, and hopefully I can clear some things up. (I am in Perth too).

I have taken one apart, still got the inner workings in the garage, ...

The centre diff shares the gearbox oil with the front diff and the gears...

My curiosity is based around this inside front wheel spin issue. Since there is not an affordable solution for a front lsd, I am curious how one might change the power output to be more rear bias. Reducing power to the front may also reduce the effects of the inside wheel spin. I am just trying to expand this idea I have been pondering on.

Really intersted in this to.. i seem to remeber from reading at the alltrac forum that there is a company in europe somewhere that does change oil on there gearboxes to make the lock up better..
will try to find it..

Mario Konig should have that info.