Join Date: Mar 2014
Location: France - down by the Spanish border
Vehicle: 2014 SLK250
Other Toys: RS3, MacanS, MGBV8
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A poor/cheap filter will catch up with you later on.
You must decide if you want your air filter to have a flow bias or ability to trap dirt. There is a trade off between one and the other. Usually for a daily driver, you will want to trap dirt - then look for the micron rating - you want one that will let in minimal particles.
What environment do you live/drive in? If dusty, then an oil impregnated one replaced often is best. If you know the environment to be pure or you are racing, then the dry green filters might be favoured.
If you really want to select the correct filter, then look at their ISO 5011 test results - this will show all sorts of things like the micron rating, flow restrictions at various dirt capacities etc. Compare the findings and you will immediately see the better filters. Do not po-poo OEM filters though...