K&N Air Filter
I have used K&N filters and other manufacturers over the years. I have learned the hard way that generally speaking the OEM filter is superior to the aftermarket filters. I had a 2001 NSX that I supercharged. The internals were stock but I was pushing around 400 hp at the wheels. That is intense for a 3100 lb car. I found that when I used the foam filter that requires spraying an oil onto it to insure it captures dirt and dust that ultimately some of the dirt gets past and covers the butterfly in the intake manifold. This then causes the car to run rough. I found that I had to clean out the intake to get everything back to normal. When I spoke to Comptech who at one time were the Tuners for Honda/Acura I was told that the OEM paper filter is superior to the aftermarket filters and protects the internals. You just need to make sure you change it periodically. After returning to OEM filters, I never had a problem again. I would check the condition of the butterfly and it would always appear really clean. So keep that in mind when you think about aftermarket filters. On a 1991 Infinity Q45a I added an aftermarket cold air filter system with a K&N filter. The system allowed significant increase in airflow. I also added a engine chip from Wolf Racing. My performance improved significantly, as did the noise of the intake. The problem was that the airfuel ratio could not adjust sufficiently for the increase in air. So I ran rather lean. The only way to eliminate detenation was to run racing fuel at 100 octane. That was rather expensive at $9.00 per gallon. Evenventually, I blew a piston crown and destroyed the block. $15,000 engine. The car was very fast though......
I am leaving the Volvo alone. Heck, I never thought I would be old enough to drive a Volvo. I do really love the car so far.