It is my understanding that the Barchetta and Punto HGT 1.8 16V engines are difficult and expensive to get more power out of them with the normal engine tuning upgrades.
I think? the reasons are:
1) Already a well designed setup with regards to head flow also with variable cam timing
2) Fairly complex intake resonator to improve induction
3) Hitachi Engine ECU is not really tuneable
To get any real increase one would have to probably go down the "low" to "mild" turbo route and also have a completely different ECU and possibly new injectors.
All very expensive.
Here is an old thread on a now defunct forum re: tuning the Barchetta Engine. See:
http://sfconline.org.uk/forum/topic.asp?TOPIC_ID=5375