Hi Surya,
BPC model can have 13 dimensions if we need best performance wise.
BW Cube also have 13 custom dimensions(chars).. while loading you may pass bpc dim = bw info object.
at BW Side there 3 sap defined dimensions which are not useful for BPC. So BW also have 13 custom dimension only.
But BW dimension is not the same bpc dimension. because bw dimension holds number char objects but BPC dimension itself is char object
Thanks