aamiggia said:
Not to Hi-Jack this thread, but why am I hearing bad things about K&N filters in 80's? Do they inject more dirt than the paper OEM filters?
Too late consider it now Hi-jacked,
yes K&N air filters do let more dirt past than paper filters,
first I ran into this was on a good friends Tacoma, he trailed it almost weekly , the local "dirt" here is fine clay, a group of trucks makes a cloud of dust. he was interested in a cleanable reusable filter as he was going through paper ones regularly, put in a K&N and regularly cleaned out the silt and re-oiled it, after a short period he started to notice a considerable build of dust in the box after the filter and in the inlet tube

, if you can see build up how much made it into the combustion chamber? how much blown past the rings? He spent more time in a dusty environment than I would or most of us would so call him the canary in the mine.
Some users report an increase in Silicon in their oil analysis when using K&N some see no change, I have not seen anyone report a decrease with using a K&N. IMO this shows than K&N’s are not as good at filtering dirt.
There is also the possibility of oil fouling the MAF sensor as mentioned above ,
Since then I have run into this test witch only reinforced my opinion of K&N Air filters
http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm
And the discussion about K&N's here @ Ih8mud:
1.
2.
4.
And at
BobIsTheOilGuy.com
Shots under a microscope of a paper towel, K&N and Paper filter, gives a visual for why this is happening.
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=15;t=000338
you can actually see these holes with the naked eye.
If you want more search the air filter section at BITOG, lots of debate between pro and anti K&N users some of it with backing evidence.
I did not and have not heard of anyone finding visible dirt in the intake tube of an 80 when using a K&N, I think this is because the centrifugal pre cleaner in the air box does a good job of getting the denser particles, it would have less effect on lofty stuff that weighs little compared to its surface area. also in my case the PO was a socker mom and never left the road,
If you drive exclusively on the street in a low dust environment, Seattle? Coastal FL? and never off road then a K&N will probably be OK but why bother? You are not going to get any more power out of a 1FZ from an air filter, the OEM filter has a large amount of surface area and as the above photo shows much more than the K&N. Even though paper is more restrictive than the cotton gauze of the K&N there is much more of it in the OEM filter that they may be even in performance,
K&N's were originally designed for carbureted American V8 hot robs used on street/track that had outgrown their stock air filters, a stock off road engine that is also expected to live for hundreds of thousands of mile is not the right application.