The 6-cylinder units shared the same 120mm cylinder stroke length, but the bore (cylinder diameter) on the larger engine was increased by 5mm to 80mm. Although a new more modern Vivastella was introduced for 1934, the earlier model continued to be listed, at an attractively lower price, in the catalogue.
The 6-cylinder engines shared the same stroke length but differed in their bore size (cylinder diameter).  A new, more modern engine was released in 1934, while the older model continued to be offered at a reduced price.