Originally Posted by sgtsmasher
depends where your getting the header from! if you go the svt header route it gets pricey, regardless of what people say unless you are good friends with an exhaust guy (i was not). dont get the M2 header or any style like it off fleebay, you would be more then wasting your money. it also depends on the style motor you have as well, they made 3 different style motors for the focus in 01. we need more info and also if you do some detailed searches in buy sell trade sections you can sometimes come across some really good deals. hope this helps
^^This guy speaks from personal experience as you can tell. lol
If you go with the long tube header and flex pipe combination you are going to turn on the CEL. Most of the long tube headers have locations as to where you can install the o2 sensors but they won't work properly. Anytime you remove the catalytic converter you are either going to need a tune to shut off the second o2 sensor or you will need to get a mil eliminator.