the reason i'm asking is if its possible to put a V8 S4 6 spd transmission on, lets say a S8?!

I think the D3 A8 has the rear timing chain....

But it has a front drive belt for all the accessories....where the S4 has a rear drive chain for the auxiliary shaft on the bottom driver's side of the motor.....

So the motors are really different in many ways from car to car.....

My understanding was that ont he the S4 and new A6 got the shortned V8 since the A8 has pleanty of room in the engine bay.

From memory the S4 and new A6 are both 340hp while the A8 is 330hp.