Originally Posted by Zman82

My thoughts on this..........obviously the driveshaft only powers the rear tires and in awd some of your torque is being sent up front depending on traction. But keep in mind that if the back end has enough traction, it will not send any power to the front. And accelerating hard in itself transfers weight to the back of the truck. If you say, put 1500lbs in the very back of the bed and did an awd or 4wd launch. It would likely be doing a wheelie, which puts 100% of the power to the rear tires and 0% to the front. So in order to save the rear driveshaft from torque damage, the best thing you can do is try to maximize front end traction and minimize rear end traction in order to get as close as possible to a 50/50 split during acceleration. It will have the least mechanical stress on all components after the transfer case.

If I had to make educated guesses in order to just have a better idea of what I'm talking about

hard 1st gear launch with an empty bed and 500hp = 65% traction at the rear end and 35% at the front, aka 325hp sent to rear driveshaft (obviously slightly less than 325hp with mechanical losses in trans/transfer case)
same with 600hp = 70% rear, aka 420hp sent to rear
same with 1000hp = 90% rear traction, aka 900hp sent to rear, (if you even have the traction possible to achieve that without spinning)

same conditions but with 1000lbs in the bed
500hp 75% rear aka 375hp to rear
600hp 80% rear aka 480hp to rear

etc etc

Now lets consider the fact that the driveshafts are engineered with torque limitations as if you always had it in 2wd, so simply by putting it in 4wd you are taking a lot of stress off that rear driveshaft.

Cliffs - if you're using street tires, and your bed is relatively empty, and you have 600hp, and your launching with awd/4wd, I seriously doubt you need to be concerned with the rear driveshaft torque limitations (still need to be concerned about high speed limitations obviously)