best thing for yours kessa is an induction kit (k+n 57i or similar) and a chip/remapp (for your specific car!!! as not swappable!!) and then an exhaust system, there are more things you can do to up the power but they involve alot of cash!!
induction kit (K+N 57i) ?75 ish
remap/chip between ?250-500
exhaust system ?300+
you could probably get about 130 bhp with this lot, the next step would prob mean getting a meatier camshaft!!
Gaz
