I saw many conflicting reports on the real value of K & N filter vs. OEM.
2 years ago, I had a chance to test an OEM and a K &N filter , back to back, on the same dyno on the same day with my 1978 Corvette (350cu.in, slightly modified)
Results:No change in HP at the rear wheel from idle to 4,500RPM. From 4,500RPM and up (stopped the test at 6,700RPM), the OEM filter delivered more RPM, with a peak of 7HP more with the OEM at 6,400RPM. The K&N rep, that withnessed the test was speechless.
Nobody can feel a 7hp improvement at 6,400RPM.
If (and only if) K&N flows more than an OEM filter, it does it at the expense of letting more dirt through. This is a simple law of physic that nobody can change. Even if it has the same filtration capacity as a OEM filter, the more air through it, the more dirt.
As far as increase in MPG, a 1 to 4MPG increase can be due to the driver, temperature, humidity, barometric pressure, and/or a combination of all those factors. For those who think they can ''feel'' a power advantage with the K & N, it has to be related to louder sound emitted by the intake system.
If K &N was such a supperior product, it would have been endorsed by a multitude of quality car manufacturers. To my knowledge, none have done so.
An other proof that a good marketing campain can sell (at a premium price) a product that is not better (sometime worst) than the original.
Just my opinion