i think that a clean stock filter will perform about the same as an aftermarket but will get clogged up faster so then the aftermarket filters will work better?
Im not sure if it was a previous thread here or on another forum but it was posted before that the K&N and the likes collect the dirt and tend to clog easier than OEM paper filters :dunno:
Also the gain wasn't worth the price compared to OEM (Bearing in mind at the time I was replacing a 318i filter)
to me the only filter that could be better is a foam filter because it works in a completely differnt way to normal filters also they are used in rally because they dont clog up and filter dust very well if constructed properly...but im not sure if foam is hte best for a bmw airbox
I was actually shopping for a BMC filter (and doing some research on the benefits) when I found this link ... I think the situation is slightly different once you start tuning the car. Then the air filter might become the bottleneck - however, for stock cars it seems that there is little conclusive benefits
I have tested stock paper filter on my 328iM against a dual cone filter and stock filter (if clean) came out best..!
Remember that this type of test are only good for the air speed simulated by the blower.
To be fair - we need to be able to vary the speed of the intake air as well.
to me the only filter that could be better is a foam filter because it works in a completely differnt way to normal filters also they are used in rally because they dont clog up and filter dust very well if constructed properly...but im not sure if foam is hte best for a bmw airbox