I owned a Q4 for a while so I should really know this... But I never really looked into how it all worked. It's a full-time mechanical 4wd but with electronic variability. The link below explains it better with some diagrams of the parts involved in the system. (Scroll down a bit to the 164 Q4 section)

Alfa-Romeo all wheel drive explained

Central epicyclic unit with Ferguson [viscous coupling], [Torsen] rear [differential] [Source|https:

m.awdwiki.com

 

OK. Does the Q4 system in the 164 share any parts with the other Q4 systems? I'm guessing the gearbox is unique, as it was he only Q4 Busso. But what about the rest?

 

It uses a unique and insane complicated 4WD system, developed (as far as i can recall) by Steyr-Puch in Austria. Practically everything around engine, gearbox and exhaust is unique, so parts are difficult/impossible to find.
There must be more info to be found on Internet...

 

The entire 4wd system is unique, made only for the 164 Q4. The engine management is also different to other 164s - different Ecu and whatnot. The engines I believe can be swapped for a different 24V busso engine with varying amounts of work depending on which version of engine you use. (166 onwards uses a different timing arrangement to the 164). The Q4 exhaust and floor pan are also different.

 

Ok. I'm surprised. So even the differentials are different? I know other Alfa Q4 systems use Torsen.

 

Multiple Q4 owner here. As said before, the Q4 uses a completely unique AWD system. The AWD is designed by Steyr - Puch and Alfa, and uses a Viscous coupling, central epicyclic differential and a Torsen LSD at the rear. Further more, the AWD system (Which is called VISCOMATIC) uses parameters from the Motronic, ABS, Steering angle, Throttle and more to decide the torque split between the axles. The Q4's torque split is variable between 0% to 100% on each axle, so it can be totally FWD, or totally RWD depending on road conditions and driver inputs.
The engine block is the same as in the QV. The only difference is the electrical systems.
The gearbox in the Q4 is designed and built by Getrag, and has 6 speeds + Reverse. The Getrag box has an open differential at the front.
The Torsen LSD at the rear works in the same principle as most other Torsen diffs. It is a 3:1 Torsen TBR (Torque Bias Ratio), and puts out torque to the loaded wheel in the corners.
There aren't any relatives which uses the same AWD system, but Mitsubishis AYC system used in the Lancer EVOs is quite similar in both components and principle of work. I have driven some EVOs, and they are in fact similar from a AWD stand point.
On ice and snow, there aren't many cars that can keep up with a 164 Q4. It feels very RWD to drive, but the speed you can drive at is just thrilling. In the summer, the Q4 feels quite overweight. And no wonder, the car weighs 1780kg.

Parts are very hard to find, and expensive. It is a nightmare to keep running. But when everything works, and you sit behind the wheel, there is no car you'd rather drive.

 

Thanks for the great info. Not easy to find info on these rare cars.

Stupid question. What happens if you would disconnect the front shafts? I'm of course talking of trying to make it RWD.

Nice looking car by the way!

 

Well, basically the 164 Q4 is FWD. So just disconecting the front shaft will not do the trick for sure: the coupling in the rear axle needs to lock up 100% all the time in that case and I would be surpriced when the electronic system reacts in the right way on a situation it is not designed for.
So... you can remove the front shafts AND remove the back diff and mount a diff from a BMW for example. AND hope that you can get a good total drive ratio in this way!

The gearbox from the 164 Q4 has a simple power take of from the front diff gear which drives the rear wheels when the fronts lost traction already and that makes the system worthless to me: it is not permanent AWD. It is just an early version of the 4Motion system from VAG. It is nice that that there is a rear TorSn diff, but again... it is not in use till the front wheels start slipping already.
And AR does it again on the Giulia and Stelvio the other way around: RWD untill it is to late and than connect the front wheels.

The Q4 systems from 156 and 159 are the way to go: Permanent AWD with TorSen C torque split differential with about 40% front and 60% to the rear in the full traction situation. The TorSen effect can vary the torque to the front and rear wheels to an higher or lower value than basic 40/60% when traction is lost on (a) front or rear wheel(s). Would be great to ad a TorSen in the rear diff.! ( the front and rear diffs are normal open diff's).

 

Well, basically the 164 Q4 is FWD. So just disconecting the front shaft will not do the trick for sure: the coupling in the rear axle needs to lock up 100% all the time in that case and I would be surpriced when the electronic system reacts in the right way on a situation it is not designed for.
So... you can remove the front shafts AND remove the back diff and mount a diff from a BMW for example. AND hope that you can get a good total drive ratio in this way!

The gearbox from the 164 Q4 has a simple power take of from the front diff gear which drives the rear wheels when the fronts lost traction already and that makes the system worthless to me: it is not permanent AWD. It is just an early version of the 4Motion system from VAG. It is nice that that there is a rear TorSn diff, but again... it is not in use till the front wheels start slipping already.
And AR does it again on the Giulia and Stelvio the other way around: RWD untill it is to late and than connect the front wheels.

The Q4 systems from 156 and 159 are the way to go: Permanent AWD with TorSen C torque split differential with about 40% front and 60% to the rear in the full traction situation. The TorSen effect can vary the torque to the front and rear wheels to an higher or lower value than basic 40/60% when traction is lost on (a) front or rear wheel(s). Would be great to ad a TorSen to rear diff. to that system! ( the front and rear diffs are normal open diff's).

 

Would the struts interchange between Q4 and fwd 164s?