On my Fiesta ST I spent £60 on a K&N air filter and about £70 on a Milltek flexi pipe - it made a considerable difference. Are there any similar suggestions on things you could do with the Crossfire?

 

Go to a muffler shop and get the rear resonators or "cats" cut out and welded in with straight pipe. Needswings Cold Air Intake, Evosport underdrive Pulley, Eurocharged tuning, larger throttle body, there's a couple things you can do.