I've got a 1.8 Zetec 105PS mk5 Escort Cabriolet that i'm looking to get a bit more punch out of rather than buying a new car.

Its already got a K&N filter on it.

I've got £1000 to spend on engine mods, what do you recommend for the most bang for my bucks? Turbo conversion would be great, but I'm guessing that would be over budget.