I've heard a rumour that to make a 16v work in an MPI Seicento, you use the same ECU and loom (I'll run a DET3 piggyback too) and change the throttle body to one from a 1.2 16v, extend the lambda sensor and you're away. how true is this? Anything I'm missing?

I found this link in the FAQ sticky:

https://www.fiatforum.com/cinquecento-seicento/93884-engine-swaps.html

Probably a good place to start.

Off topic, been following your Sei since the Punto GT breakes videos poped up in my recomendations. Why are you going with 1.2 16v? You can easily get 80hp out of the 8v and on top of that you can strap a turbo to it. Also why are you going with a piggy-back and not with stand alone? What is happening with a dash? Phfff I'm so excited for this build