What is very rapidly apparanent from this illustration is that there is remarkably little difference between the four different filters tested. The K&N filter differed from the others here in being of cotton guaze construction- the others being made of varying grades of oiled layered foam.

The second thing to note is the dip in the standard filter equiped engine torque curve at around 3,500rpm (1). This corresponds to the rev range typically employed in urban areas, resulting in sluggish pick up to throttle. Interestingly, all the aftermarket panels irradicated this torque dip, resulting in a far smoother torque curve.

For clarification, I have included this simplified graph demonstrating the power and torque curves of just one representative panel filter, in this case the K&N product.

K&N panel filter is shown with the open squares, the standard filter, the open circles.

Maximum power gain is only a couple of bhp, but the advantage here are the more linear power and torque curves.