most car already have CAI, ours are 1 of them, a short ram to draw cold are from the front to our airbox, and will the paper filter to filter out particulars from the air into our throttle.
many ppl change it due to they needs "more" air in to the throttle, so, they change it to a bigger diameter ram to draw more cold air into the airbox, same time also need to change to high flow filter to allow more air to get into the throttle smoothly and faster air flow.
some even want more & better flow of amount of air with less restriction/blockage, they change it to an open pod filter.