There are conflicting views about the improvements obtained by replacing your car’s air filters to K&N Stock Replacement Drop-In Air Filters, with claims that due to the larger pores allowing more air into the engine for increased performance, it also allows in more dirt, potentially causing engine wear.
Personally, I think these washable cotton-pleat filters are ok, provided that they are cleaned periodically or when necessary using the right methods, and more importantly that they are oiled as per manufacturer’s instruction.
No matter how “large” the pores are supposedly claimed to be, I believe they are still not large enough to allow dirt big and coarse enough to cause engine wear. Anything too small that can possibly get past the pores is probably too fine to cause damage and not very different in size from those that are let in through stock paper or synthetic air filters.
The oil layer on the air filter acts as a tacking agent to capture these minute particles. You would do more damage by not replacing your engine oil following the recommended frequency regardless of the type of filter used. However, we will save this argument for another day.
Today, I’m going to show how I replaced the standard stock air filter in the Alfa Romeo 147 with a suitable washable cotton-type drop-in air filter by K&N – Part No.33-2218. You can get the correct Part No. for your car make and model on the K&N website, or click here to begin your search on Amazon – be absolutely sure to select the right K&N air filter based on your car model!
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Removing and Replacing the Air Filter
1. Open the car bonnet and find the air filter box, which is located next to and below the fuse and relay box. You will see two large clips that keep the filter box cover tightly closed to the filter box. This cover is connected to an elbow hose, which is then attached to the mass air flow (MAF) sensor housing, as shown in the next photo.2. As the air filter box is located in rather tight space, it may help to remove the filter box cover WITH the elbow hose entirely from the assembly. Use a pair of pliers to unhook the clip and detach the hose from the MAF sensor housing.3. Detach the elbow hose from the MAF sensor housing (the one with plastic mesh protection) with a slight pull and twist movement.4. Unlatch the 2 large clips and remove the filter box cover. You should be able to see the stock paper air filter (seen in yellow colour in the photo above).5. Remove the stock air filter from the air filter box.6. With the air filter removed, take this opportunity to wipe the inside of the box with a damp tissue or cloth.
K&N AIR FILTER – SELECT FOR CORRECT CAR MODEL
7. Remove the new K&N filter from its packaging and inspect it, making sure there are no manufacturing defects such as holes, and that the cotton pleat has been oiled. This is usually already done by the manufacturer, with the cotton pleats or filter medium appearing red due to the actual colour of the oil.8. For the Alfa Romeo 147, I have found that the K&N filter required a little trimming in order for it to fit into the filter box nicely. Without this trimming, the cover could not be closed properly. Only one shorter side of the filter lip (width side) needed to be trimmed off as shown in the picture. This filter side will later be on the top side of the filter box.9. Remember that only the upper lip needs trimming, not the entire side or you may ruin a good air seal. CAUTION: THIS MAY VOID THE WARRANTY ON YOUR AIR FILTER, SO PROCEED AT YOUR OWN DISCRETION. Note: You may want to try installing the air filter without this modification first.10. Seat the new K&N filter firmly in its box. Make sure all four edges of the filter is touching the box, and that the filter can go in no further.11. Replace the filter box cover and latch back the two large clips as shown. You should be able to see the lip of the filter between the cover and the box if you had not trimmed it. You can see here how the lip provides a good air seal once the cover is in place.12. With the filter box cover replaced, reconnect back the elbow hose to the MAF sensor housing and fasten back the clip with a pair of pliers. That’s all there is to install K&N air filter for the Alfa Romeo 147!
