I average about 38mpg with mixed driving. Same car with 110k on the clock.

I thought about tinkering with it... But even with exhaust, cams, inlet and remap you're only looking at about 190bhp maximum (if you believe the claims for the Fiesta ST). The ST220 will still be another 30bhp more powerful and you could buy one for the amount of money it will cost you to do your car up.

I wouldn't bother mate personally