You can buy an induction kit that is just the filter in a cage and it clips on to the bottom of the metering unit. Sounds bloody awsome (especially on your V6), kills fuel efficiency. But you get the best airflow. Not sure if they do one for the XR4i thou.

Or you can just put in a performance filter into the box and leave as it to keep the noise down. Not as effective with the airflow as the full induction kit but an impreovement.

As above but drill the box for the induction noise and improved airflow.

But to be honest I wouldn't bother untill you have had work done to the head and need the de-restriced airflow. Otherwise you just kill your fuel efficiency for the smallest gain in power.