A K&N air filter is the most cost effective, reliable, and simplest way to get your car ready for a stage 2+ ECU Upgrade.
We prefer the K&N drop in filter over a cold air intake (CAI) system for several reasons. First off its much easier to install. Second is that its performance is comparable to a CAI due to Saabs stock high volume intake systems. Lastly is the price, a drop in K&N is much cheaper than a decent CAI. Another reason we prefer a K&N is its reliability, they really do last the life of your vehicle. This saves money in the long run from buying replacement paper air filters every 15K miles. Add in the peace of mind of knowing you have something more substantial than a few layers of paper protecting your investment and the choice is easy.
Be sure to invest in a K&N recharger kit, its a must have when you own an K&N filter. We carry the kits with the aerosol filter oil which really helps to apply a light coat (vs. the squeeze bottles).
Brew City Boost recommends going "easy" on the K&N filter recharging oil (not included) when servicing your air K&N air filter. If its put on too heavy it can build up on your MAF sensor and cause issues. And always remember to only put oil on the correct side of the filter.