[Disclaimer: At the outset we would caveat that this blog is not intended to be a selling tool for K&N airfilters and we advice you to decide on the purchase of a K&N or OEM / after-market filters based on your specific research and requirements]
To understand the K&N air filter, one needs to understand what an ordinary air filter is and what it does.
What is the purpose of an airfilter?
And to understand that we need to know how power is produced in an Internal Combustion Engine – In layman’s terms, when you step on the accelerator pedal, it opens a throttle valve which sucks air into the cylinder through an air duct that is exposed to the atmosphere. This air flows through an air filter before entering the throttle valve. The more you press the pedal, the more air (and fuel) is introduced into the system. As soon as air enters the cylinder, fuel is injected and the piston moves up to compress this air. Due to high pressure and temperature (and a spark in case of petrol engines) the mixture explodes, pushing the piston down, transferring different types of forces through a system of components – crankshaft, gearbox, axle, differential, drive shafts which ultimately turn the wheels of your car.
It is important that the air being sucked into the engine is clean and sufficient to allow complete combustion. If there are any particulates or abrasives present in the air, it can cause mechanical wear of the cylinder and pistons and engine oil contamination. And thus reduce engine performance and engine life over a period of time.
As the name suggests, an airfilter filters the air that enters the car’s engine.
An airfilter has a conflicting requirement which is to not impede airflow into the engine (if technically possible, allow ‘unrestricted’ flow of clean air into the engine). If air (oxygen) into the engine is restricted it could result in lower throttle response, reduced horsepower, lower mileage (to some extent) and even black smoke (due to incomplete combustion).
Simply put, two purposes – filtration and yet maintain proper airflow during the course of its life!
By understanding how K&N filters are designed and built to achieve both these objectives will provide answers the headline question.
Most stock or normal OEM air filters are made up of pleated paper or foam filter elements and fibrous materials with pores small enough to trap solid particulate matter or dust from the air. Due to high pollution levels, air filters tend to get choked with particulate matter and it is recommended to either clean or replace an air filter at every general service of your car. The air filter has a direct impact on the amount of (clean) air being supplied to the engine – If the pores are too tiny, it may have better filtration qualities but effectively restricts air flow. Also if the filter is choked with particles over a period of time, then less amount of air (and hence oxygen) are supplied to the engine.
On the other hand a K&N air filter is said to be made up of layers of cotton gauze layered between sheets of aluminum wire mesh. Thousands of microscopic cotton gauze fibers naturally hold specially designed oil in suspension to create a powerful filtering medium. The filtering medium is able to capture and hold dust particles that are much smaller than the actual size of the opening in the fibres.
A stock paper based filter loads its surface with dust in due course of driving while in the case of a K&N filter, there are multiple layers of fibres holding dust particles. Thus a K&N filter claims to effectively hold more dirt per square inch than a paper filter.
(Note – We havent been able to find any independent scientific test lab results which show the K&N filter is better in filtration capability than a paper based OEM filter)
Its a known fact that the filtration capability of any filter is inversely proportional to airflow rate in any paper based filter. Hence a paper filter that provide adequate filtration will be restrictive to airflow. And as the filter collects dust particles, they effectively choke the pores in the filter which then block airflow further.
In the case of a K&N filter, the manufacturer claims that it is designed to achieve high, virtually unrestricted airflow while maintaining filtration levels critical to long engine life. The dirt particles collected on the surface of the fibres in a K&N element (apparently) do not affect the airflow because there are no holes to clog.
There are several demonstrations that have proven K&N high performance airfilters (and similar cotton fibre filters) offer better airflow through the filter (measured in terms of pressure difference across the two sides of the filter element).
Replacement, Cleaning, Economics
Airfilters are typically replaced at every service interval or every alternate service interval depending on the make/model of your car. Volkswagens change their filters every service interval whereas Hyundai’s and Maruti’s change their filters every alternate service interval. (Note – our recommendation is to replace the airfilter based on condition / need irrespective of the service interval)
K&N recommends their airfilters be cleaned every 50.000 miles / 80,000 kms (although we suggest you clean them based on condition, for e.g. if you are driving predominantly in high dust areas). A separate cleaning kit is available for purchase for cleaning and reoiling the filter. Each cleaning kit can be used 10 times to clean a K&N air filter! K&N provides a “million mile limited warranty” (read exclusions here: http://www.knfilters.co.uk/warranty.aspx).
In terms of economics, a normal OEM airfilter costs between ₹300-800 on an average and the K&N equivalent costs between ₹4000-6000 so roughly 8-10 times. For a value conscious car owner, unless you maintain your K&N filter well and clock a lot of miles (30-40,000 km per year), you may not see a payback within a typical ownership period of roughly 5 years.
Some other myths and truths surrounding K&N airfilters
- x% increase in fuel economy: Neither does K&N proclaim nor it is to be expected that fuel economy will increase just with replacement of a stock filter with the K&N filter
- Dramatic increase in horsepower: The mere addition of a high performance airfilter (=more airflow) cannot increase horsepower of the engine unless other modifications are done to the inlet manifold and the ECU. However lowering the impediment to airflow into the engine does translate to better throttle response and some increase in horsepower (which again is difficult to ascertain even when tested on a dynamometer). Gains can be felt at higher RPM and wide open throttle (WOT) while driving
- Validity of OEM warranty – well any aftermarket part used in the vehicle can technically void your manufacturer warranty!
- Oil flowing from the K&N filter affects the functioning of the MAF sensor – again, no convincing evidence of this and K&N has been selling hundreds of thousand of airfilters every year and would not have been the case if it there was a serious issue. Having said that improper re-oiling of the filter will definitely cause issues.
As you may have realized by now, K&N airfilters are not for the casual car owner. If you are looking for performance gains at high RPMs and not really driving in a dust bowl environment everyday, if you are willing to work with your car and keep the filter cleaned regularly as recommended, it might be a worthwhile investment.