Filters offer a cheap and easy way to improve the performance of your EXA. Many aftermarket filters (such as K&N, UniFilter, HKS, etc) improve airflow and extend time before servicing them. Midrange torque and high-end torque should improve noticably, but it works even better if you have an exhaust system and/or powerchip.
Pod-type filters aren't an easy fit in the Nissan EXA (CA18DE). Simply because the airbox is removed and the EFI sensors are attached to this box. This means you must custom fabricate a bracket to hold the sensors. Also you'll be drawing more heat from the already tight engine bay, so you may have to think about cold air induction and a custom box to house the pod.
Personally, I don't like to stuff around so I picked up a K&N replacement filter which sits in the original air box.
This took about 5 minutes to install and the results were instant. Torque improves slightly and fuel economy is also a bonus. Averaging about 10.5L/100km even on premium unleaded petrol and driving fairly hard. The cost? $95Aust for the filter. For an aftermarket air filter to work properly, I'd highly recommend fabricating a cold air induction pipe. I was so amazed with the results that I've created a whole new page on cold air induction, check it out!