excellent thread!
Air filters are the first line of defence for automotive engines during the combustion process but unfortunately there is very little data available in Pakistan regarding airfilters available here since there is no real law stating that filters available here have to provide any data or undergo any testing etc.
Now in simple terms ALL air filters can filter particles down to 1 micron, but they will not be very efficient at it. Infact many filter manufacturers abroad have claimed that their filters can filter down to 5 microns, which techinically is true, but then again even a mosquito net can filter that low,.. but not efficiently. normal filters (usually made of paper and cotton gauze etc) are rated at certain particle sizes, for example some filters are 97% efficient at 30 microns (but might be 10% efficient at 29 microns etc). This does not mean that they cannot filter larger particles (obviously) but that at 30 microns it's at it's optimum efficiency.
In an ideal world we'd all be using high capacity foam filters for out air intakes since they would filter all sorts of sizes of particles and since the path of air is "baffled" the chances of particles getting caught are higher due to the next-to-infinite surface area. Also most good aftermarket foam filters have been proven to be more efficient than any OEM/off-the-shelf paper or cotton gauze filter. The reason filtering efficiency is important for the air intake is becuase whatever gets by usually ends up in the oil either pre or post combustion. like most OEM air filters, OEM oil filters (and most aftermarket ones) aren't too good at filterin partilces under 30 microns and sadly these are the particles which cause the most damage to an engine as they are abbrasive .
Never skimp on any filter for your engine or it'll not last as logn as it is supposed to (specially in our fine-dust environment), and please don't be fooled by "cold air intakes" which provide "intake sound" for EFI engines,.. they are usually made with the most inferior materials and 99.9% of the filters available in PK are worse than the original ones fit to your car from the dealership (applies to all manufacturers). Most aftermarket filters available in PK are probably 90% efficient at 100 microns,.. you can imagine the rest.
