Now its just habit...replacing the Air Filter with a K & N Filter, but years back when I was in Auto Cross Racing...they added horse- power...A engine runs better if the air coming into the Mass Sensor is cooler and densier. The air Flow is usually much better than stock air filters, thus allowing your car to breathe better at higher RPM's, thus producing more Horsepower...but with today's engine management systems...the effects are minimal unless you modify the air intake with an aftermarket air intake system or re-route your existing intake system...My Foci ZX3...is a lease vehicle so I am not making many changes to this car...nothing that I can't put back after I am done with it.

Is this something you get at Schuck's and is it expensive? More horsepower would be nice, but I'm really looking for things that will give better mileage at the moment. If modifications would do both and save me gas money, I'd be willing to put some money into that as I'm not leasing. Thanks for your info! Northender 2001 Everett, WA

Any auto parts place can order this custom hi-performance air filter. I paid $44 for mine. As for the mileage increase...sad to say..you get what you get. Ford could have choosen taller gears for better performance, but the company decided to go the performance route with Focus...the old escort was panned for its lack of performance except for a few select models. After researching the Foci, I knew going in that the mileage was not as posted but you hope for the best..My gas mileage has improved. Not much but some, not that I am worried since I also have a diesel New Beetle that serves that purpose well for road trips.