OK, I checked out a VW SSP (Self-Study Programme) PDF that I have on the W-engine family, so this info can only apply authoritatively to that engine. However, the W engines are basically 2 15° VR engines siamesed with a 72° major bank angle, so it stands to reason that things like cylinder offset that apply to each minor bank should also apply to the VR engines on which they're based.
The above link to a page on the SSP document (there is no copyright mark, I checked) shows that the minor bank does indeed have a 12.5mm cylinder offset, but what is incredible is that the offset are on opposite sides of the crankshaft centerline (!!!), with the intersection point below said crankshaft centerline. This means that the motions of the left-minor bank will be slightly different than the right-minor bank!! This also means that the articulating angle of the connecting rods are different at given crank angles and, particularly close to TDC, in fact on opposite sides of the cylinder axis.
Given a 90.3mm stroke of the first-generation 2.8 VR6, 164mm con rod length, ±12.5mm cylinder offset and assumed zero piston-pin offset, maximum true stroke is 90.585mm. On the right bank with positive cylinder offset (toward the anti-thrust side) the maximum stroke length occurs at 186° CA (referenced to TDC), and the pistons' closest approach to true TDC occurs at +3°CA (0.0016mm below true TDC). On the left bank with negative cylinder offset, the same maximum stroke length of 90.585mm occurs at 174° CA and closest approach to true TDC occurs at -3°CA (also 0.0016mm below true TDC).
On another note, a slight piston pin offset (usually 0.5 to 2 percent of piston diameter) is introduced mainly for NVH purposes in order to smooth out the transition of the piston skirt position, which wants to stick to the anti-thrust side on the upward portion of the stroke and to the thrust side on the downward part.
Interesting stuff!
