Re: Can someone explain QTII a little better to me?
Its not a full lock system that's set up for 100%. QT II can put about 90% of engine power on one axle or the other. QD adds a limited slip to the rear dif (90%), so eventually about 80% of the engine power is delivered to one rear or the other when the other wheels are off the ground. Limited slip is not available for the front, so the max front tire power is 45% when all other wheels are off the ground.
Brake traction has about a 50% power loss. So with a completely open QT I system, the max power to any one wheel when the others lose traction is about 25% of the engine power (50% in the axle, 50% transfer case). For the QT II system, with its limited slip transfer case, it is about 45% of engine power to the wheel with traction. For QD, rear wheels its about 80% of the engine power, front wheel about 45%. The rest of the engine power is used to make brake heat.
So QDII has an advantage getting engine power to the ground on steep slopes, negotiating rocks, or deep stuff, other things being equal. In the real world, things are rarely equal. Good tires and driving will make more of a difference.
BTW, QTII and QDII have a transfer case lock position so full 100% of torque can go to the axle with traction instead of the 90%.
You may ask why not full lock transfer case and difs as that will get you 100% of the power to the wheel with traction... that is a dangerous vehicle to drive where there is good traction. It takes quite a bit of driver skill to operate full lockers safely and to get the most out of them.
These are rough numbers for illustration. There are numerous other factors, like speed of detecting spin, sensitivity... etc that also make a difference in the real world.