The V3 is better reinforced than the V2. It has extra metal in it where the V2 doesn't. You get less of a problem with cracking and hair-line fractures.Peyote said:
To add onto this (Although none of this matters for the fusion engine) the V3 has the motor attached to the gearbox as well.
I kind of wish they'd make a V2 with the same reinforcements as a V3.