PARC,
The standard head ported with oversized valves and suitable cams will get you over 200BHP from either a 1.6 or 1.8 . At 180 BHP and 7800rpm you start to push your luck with engine strength. First requirement Forged pistons. The VVC head fully ported with oversized valves will take you well over 200bhp and possibly up to 250bhp. Over 200bhp and 8000rpm strengthening the bottom end, steel rods, crank and stronger liners are recomended. Sadly the expense doen`t stop there,increased capacity injectors, fuel pump, drysump, clutch etc etc ect.,