M xDRIVE.

In 4WD Sport is the power fixed between both axles?

No, torque split is a fully variable distribution at all times in 4WD and 4WD Sport mode. In comparison, 4WD Sport mode allows for more rear wheel slip than 4WD mode before sending more power to the front wheels.
To improve steering behaviour and cornering power of the front axle, we especially lower the front axle torque while cornering.

Peter what do you mean "Drive to the front wheels will be switched off for efficiency"?

The M xDrive can dial in fully variable torque split between front axle and rear axle. It is possible to manually switch of the front axle --> 2WD mode. Based on the given driving conditions, e.g. constant highway cruising, the system will also automatically decouple the front axle in 4WD and 4WD Sport mode to operate more efficiently.

Will there be an option for manual transmission in AWD cars?

No, it won't.

Does the camber of the wheels for the M3/M4 with M xDrive remain the same compared to RWD?

RWD models have a front axle camber of -1°40'. AWD models have a front axle camber of -1°30'. Rear axle camber is -1°50' for all models.

Is the front differential equipped with lock like the rear end is?

The front differential is an open differential without an integrated mechanical lock.

What type of clutch is used for the coupling of the front drivetrain?

That is a multi-clutch type coupling.

Is the clutch pack designed to slip in order to have different speeds at the front and rear?

Yes, it is.

When the clutch pack is fully engaged, how does it allow for front wheels to spin at different speeds?

When the driving situation allows for equal wheel speed at all wheels, the clutch can be fully engaged. At conditions where different individual wheel speeds are required the clutch will be partially open.

What is the reaction time of the system engaging/disengaging the AWD?

Normally, just the torque transfer to the front axle is varied, its variation takes less than 150ms. Returning from efficiency mode shift time is less than 400ms.

Why use a chain in the transfer case instead of pinion gears?

A chain drive produces less noise and drag.

Main difference between AWD in the M340i and in the M3 (beside the switch off option)?

Compared to the M340i and M440i xDrive models, there is more rear bias with the BMW M3 and M4 models with M xDrive. Additionally, the M3 and M4 models feature the integrated torque control system for faster adjustments and the transfer case / clutch pack is a beefed up version for more driving dynamics. Another difference are of course the three modes 4WD, 4WD Sport, 2WD.

So even in 4WD, the torque is sent to the front only when needed? Or there is always some torque going?

The front axle torque split can go as low as 0% even in 4WD or 4WD Sport mode depending on the actual driving situation - think of steady highway cruising as an example.

Does the horsepower output change between 4WD and 2WD modes?

No, it is always the same power that is being sent to the wheels - no matter if 4WD, 4WD Sport or 2WD.

Does AWD set better lap times?

That completely depends on the particular track and the environmental conditions.