you will find it hard extracting power from n/a engines without major mods, most companys will say with there mods you will see up to, they never give exact figures. ie pumaspeed say they can tune the fiesta st to 185 bhp, from the standard 150, i know 7 people that paid for it and never seen more than 170.
but on another note, do you trust the dyno, i tuned a diesel focus from 113 bhp to 138 bhp on 1 rr, went to another and it said 121 bhp. also being in malta i would be inclinde to say the atmosphere is hot, this is not good for big power
supercharging and turbo charging is the best way, but thats big money,