Bought a low mi 2014 4 in early 2020 after foolishly selling our red ‘11 4 with only 118k mi to ease move ME-FL. Was barely broken in/perfect inside/out. The 14 was not getting MPG we were accustomed to, so checked/replaced clean oil and found a K&N in air box. Was clean, but K&N’s screen was huge. MPGs came up indicating viscosity was culprit. Not convinced K&N useful in anything more than racing rigs?
The K&N filter tests were done by dumping "dirt" of a known size into an air-stream at a constant rate and over the equivalent of several thousands of miles measuring what got through on the test rig. Not only were there more particles but they were bigger. Consumer Unions and one of the Car mags did similar tests probably 5+ years ago.
