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My mechanic after some persuasion by me bought a Q2 differential in order to find if it is possible to retrofit it to an existing Alfa. Here's what we have found so far.
First of all, the Q2 is an epicyclical torque-biasing diff of type Torsen B without a preload spring, like Quaife's ATB. Here is a drawing of it:
Its shell is of similar dimensions with the free diff of the TS versions but the ring gear spigot is a little wider. Also the driveshaft spigots are longer; about twice the length of the ones in the free diff. Therefore in order to fit the Q2 to a TS gearbox you would have to machine away a portion of the spigots and fit the ring gear of the JTD Q2 version. This ring gear however is quite "long" in ratio, 57 teeth. For a 1.6 147 like mine it could be combined with a 14-tooth pinion gear, from an earlier 155 model instead of the stock 15-tooth pinion gear and the final ratio is really close, (57/14=) 4.07 from (61/15=) 4.06. For a 2.0 TS i am not sure because we haven't found what kind of ring/pinion combination they use.
I'll keep you informed about anything new we may find.
First of all, the Q2 is an epicyclical torque-biasing diff of type Torsen B without a preload spring, like Quaife's ATB. Here is a drawing of it:

Its shell is of similar dimensions with the free diff of the TS versions but the ring gear spigot is a little wider. Also the driveshaft spigots are longer; about twice the length of the ones in the free diff. Therefore in order to fit the Q2 to a TS gearbox you would have to machine away a portion of the spigots and fit the ring gear of the JTD Q2 version. This ring gear however is quite "long" in ratio, 57 teeth. For a 1.6 147 like mine it could be combined with a 14-tooth pinion gear, from an earlier 155 model instead of the stock 15-tooth pinion gear and the final ratio is really close, (57/14=) 4.07 from (61/15=) 4.06. For a 2.0 TS i am not sure because we haven't found what kind of ring/pinion combination they use.
This is not true, read ahead in the thread.Unfortunately the Q2 cannot fit into a V6 gearbox because the V6's ring gear is larger than the TS or JTD one and its bolts are totally different.
I'll keep you informed about anything new we may find.