Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Cold air intake for 7.3 powerstroke

I have used K&N; air filters exclusively for the past 15 years and they work great. The diesel engines use a lot of air and the air filters see a lot of bugs, dust , etc, so the air filters tend to clog quicker and really don't clean ups o well, so instead of reusing them, I typically replace them every 30 or 40,000 miles, depending on how dirty they become. No matter how dirty they become though, they are a big improvement over paper filters.. In my cars, they last about 100,000 miles before I replace and I clean them every 30,000. Mileage and power seem to be better than stock, but not as much an improvement as claimed by K&N..;Ken