K&N high-performance air intake systems are designed to maximize airflow and reduce turbulence. This is achieved through an aerodynamic path and a filter design that increases the volume of air reaching the engine. The result is more horsepower and improved acceleration. To prove this, Jason Fenske from Engineering Explained tested a K&N air filter on a Subaru Crosstrek and found that it produced 164.3 hp and 142.5 lb-ft of torque.
For even greater gains, a complete cold air intake system should be installed. Most 77 Series intake systems have been declared exempt by the California Air Resources Board for applications in which each system is included. The usable filter portion of the effective filter area is calculated by multiplying the filter diameter by pi (3.141), multiplying by the height of the air cleaner in inches, and then subtracting. Each kit undergoes significant testing to help ensure that the filter and intake pipe are positioned to deliver large increases in airflow and power.
Dynamometer tests that indicate estimated increases in horsepower and torque compared to the OEM intake system will appear on the Product Details page for each high-performance exhaust system. To provide an even larger air volume to the engine, install the largest filter that fits in the allocated space. Short Ram (SR) intake systems use a one-piece intake pipe and locate the oversized K&N clamp filter at the original air box location. Alternatively, complete cold air intake (CCA) systems use a two-piece intake pipe and can be converted from a cold air system to a short ram system, in case of inclement weather, to prevent water ingestion by the engine.
The intake pipe houses the factory air mass sensor and a replacement silicone crankcase vent hose. Static pressures often vary from unit to unit, as conduits and factors other than the filter can influence pressure readings. For example, a filter 10 inches in diameter and 2 inches in height will provide more airflow than a filter 5 inches in diameter and 4 inches in height. Well, Fenske's tests revealed that high-performance air filters do indeed produce more power, but they also found that the paper used in filters was an important part of the problem - it's excellent for filtration but bad for airflow. While both types of filters trap contaminants, they are composed of different types of filter media and are not interchangeable.