I had one in my gas truck and for over 100,000 miles, I never had to buy an air filter. Just kept it cleaned and oiled and it was fine. If there was any increase in power or gas mileage, it wasn't really enough to notice, but it did sound cool. Like Iggy said, it had a little roar to it with the K&N.
Ed and Sharon
2010 Wildcat 28RKBS
2011 Ford F-250 XLT, 6.7L PSD
Ride-Rite Airbags and Airlift wireless remote compressor...nice!
I thought I was wrong once, but I was wrong!