948 Oil Filter Conversion Kit
Oil filtration on the 803 and 948cc engine is implemented as a bypass system. This means that a small quantity of oil is diverted through the filter as it is pumped around the engine. By comparison, the 1147cc and larger engines in this family have a full-flow filtration system, so ALL of the oil passes through the filter as it is pumped.
The full flow filtration system is obviously better, but changing this really isn't an option here. The best we can do is make use of the latter system's readily available filter.
Bill Davies including pictures