It's debatable whether this Hack does much for performance, but it adds a nice sound to the engine under load.
Flat-head Screwdriver or 10mm socket with extension
About 45 Seconds :)
1) Open the hood.
2) Locate Airbox. Towards the driver's side fender you'll see a small box attached to it. That's the resonator. We're taking that guy OFF!
3) Using a screwdriver or socket, loosen the 2 screws on the airbox that are closest to this Resonator. Three turns ought to do it.
4) Pull up on the airbox.
5) Pry the resonator away from the airbox.
6) The lower part will still be connected. Pull the lower part of the resonator firmly away from the airbox until it pops out.
7) Observe the new air entrance point!
8) Tighten the screws you loosened.
9) Start the car and rev it. Hear the difference!
10) Close everything up.
* Note: For North American Foci, this applies only to 8v 2.0L SPI and 16v 2.0L Zetec-E engines. This excludes the 16v 2.3L Duratec (PZEV)