All cars now will have a MAF (mass airflow) sensor connected to the intake somewhere! By the sounds of it this is a universal induction kit? ie will fit all cars and not model specific?
I would highly advise against such a mod! Reason being ford have spent time developing an airbox which will allow adequate air in whilst sheilding the intake from engine bay heat (heat soak) you will take a drop in performance if you just replace the airbox will a universal cone filter regardless if its a good brand such as k&n!
Instead just buy a k&n panel filter to replace the stock filter inside your current airbox! If you have an airbox with a stock cone shape filter i would recommend a green cotton replacement or the K&N 57s kit which only replaces the stock cone for a bigger one and a reshaped airbox lid to increase airflow
Exellent answer! exept the K&N 57s i have looked at do not appear to be fully encapsulated (allows warm underbonnet air into the filter) - you need to go for the BMC CDA or Pipercross Venom for fully - encapsulated cone filters
The Mk1 Focuses have flat - panel style filters - the 1.6/1.8/2.0L & RS use the same filter
Scott - can you let us into your secret? - is your mk 1 Focus a petrol or diesel? whats the engine capacity/ type?
PS - welcome to the forum!