I realize that a CAI is usually one of the first mods that many pursue so I guess I did it backwards. My car already has a TSX intake manifold, a DC Sports header, and a custom 2.5" exhaust...with the stock air box. Unfortunately, I cracked my air box while servicing it (doh!) and needed a replacement...perfect excuse to install a CAI. After weighing my options, the K&N set up was the only CAI that included everything required for a complete install, had a custom designed heat shield, and was CARB legal. It was also the most expensive. So I did some searching and found a new, open box kit @40% off. Installation took only 1hr in my driveway with common hand tools, taking my time. The end result was...ummm....okay?? Yes, it does make "thoaty-er" intake sounds...but only slightly louder than what the TSX manifold had already provided. As for performance, I've already experienced noticeable gains with the previous mods and it quickly became obvious that this new K&N kit wasn't going to make a big difference. However, I do like the more intimidating sound as well as the appearance under the hood(...and the fact that I didn't pay $400 for it!).

Edit: Perhaps I was too soon to judge the increase in my powerband. That or I needed to drive a few more miles for the ECU to adapt. In any case, I eventually did discover where the increase in HP is...@ upper mid-range & high RPMs. I climb the same hill everyday on my way into work. My existing mods did a pretty good job and the car easily accelerates up the steep hill. With the new intake installed, the car really came to life as I approached 4k rpms and continued to pull as I reached 5k. The difference was noticeable enough that it did briefly cross my mind that the front wheels could break traction and caused me to lift on the throttle slightly. The sound during the climb was nothing short of hellacious compared to the quiet stock set-up.