This is a question which has been long debated. There are those who swear by K&N filters, and many who swear at them. From ‘Autoblog:’:http://www.autoblog.com/entry/1234000600057664/
Fortunately, a Duramax owner tired of the lack of scientific evidence pursued a path of testing that eventually ended with a lab performing the ISO 5011 procedure on a number of replacement air filters.
Read the ‘full test results here’:http://home.usadatanet.net/%7Ejbplock/ISO5011/SPICER.htm. The gist of the tests is:
The K&N and UNI filters were far less efficient at trapping dust, and note that they lose their flow advantage after filtering about 180 grams of dust.
From the ‘Impala SS Forum’:http://impalassforum.com/noncgi/ultimatebb.php?ubb=get_topic;f=8;t=015894
bq.. any cotton oil gauze filter is not going to filter as well as a paper filter period. Cotton gauze offer flow over filtering. More or less it’s a Cold air intakes new intake tract or location that will see the gain. If they made a paper cone filter to fit the Raiss I’d prolly run it.
Note from reading on the oil forums a dirty K&N or similiar filters better than a clean one. Also note that K&N is considered garbage in the performance filter area due to it’s poor construction, lack of pleats, and the ability to see light through the filtering element when held up to the light. S&B by far is considered to be a far superior filter to K&N. Personally if you don’t drive in really dusty conditons then use whatever you want, but if you’re in a heavyily dust enriched envir. then use paper.
It has to be said, bolting on a K&N filter kit does increase horsepower – but not because of the less restrictive filter, but because generally people end up changing the entire intake pipe to the manifold with the far less restrictive one which comes with the K&N kit for their car – so the reports of increased horsepower are true in those cases. But, just changing the filter only, according to any forums reports doesn’t do anything.
Most of the locally built jeeps have a filter box too small for the engine – so on these cars removing the filter box and attaching a K&N filter does increase performance – on turbo engines it can be up to 25%! Again though, it was the removal of the restrictive filter box from the air intake which caused the increase in horsepower, and not the addition of the cotton filter.
The general consensus seems to be that paper filters are the best when it comes to filtration, so for dusty conditions like we have in Pakistan a cotton gauze filter like the K&N is a bad idea.
- ‘An interesting discussion at a BMW forum’:http://member.rivernet.com.au/btaylor/BMWText/technical/K&NFilters.html
- ‘TWMX All Access: K&N Engineering’:http://www.transworldmotocross.com/mx/features/article/0,13190,1083863,00.html
- ‘Air Filtration and Flow Test’:http://www.bobistheoilguy.com/airfilter/airtest1.htm :: Another comprehensive test.