the trouble with open cones on the focus is the possition in the engine bay. most fit them where the original air box sits which has NO air flow at all as it completely enclosed on all sides behind the battery, inner wing, bonnet and gear box mount so only ever sucks in hot air causing running issues. i have come accross a 1.6 with open cone that failed its mot on emmisions 100% down to the open cone.

if i was to ever fit an open cone to my focus i'd relocate the battery either to the air box possition or in the boot (if i turn it into a track car) and then route the filter down low in front of the gear box. its the only decent place for it.

i currently run a k&n pannel filter with uprated cold air feed to the air box. i chopped the fins off the bottom and fitted a larger flexi pipe with a hose clamp and routed it to the lower grill. works ok imho.