if i am thinking about an engine swap - from 1.3 to 1.5 - please help

[mikeukrainetz]

just out of curiosity from reading over this thread;
ALL diesel engines which leave the factory, never mind the model seem to be extremely de-tuned. Ive seen what must be a hundred different engine tuners, parts etc for diesels which increase the ouput by ridiculous amounts. Anybody think this would hold true even on the little D4D? If its running at even the same power output (or even slightly less) would it not be possible to 'tune' it per se with the same power percentage increases as larger diesels?
Keep in mind Ive never owned, run, or worked on diesels.