Right. I have found sources that say that NSU was experimenting with a 400cc motorcycle-derived engine. When bored out to 600cc it later became the basis for engine in the NSU Prinz. Is that the one?
This NSU-Fiat has nothing to do with the NSU prototypes finally evolving into the Prinz. The similar engine size is pure coincidence. NSU-Fiat and NSU were two different companies.
..which can also be explained by the fact that the NSU Prinz engine is an air-cooled parallel-twin like the Fiat 500 Nuova, and we are talking here about a opposed two-cylinder-engine.
