Here is a link to a study done comparing different airfilters. I was suprised by some of the tests and the results.

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

I saw the article several months ago. As far as flat filters the AC Delco looks like number one to me. :grinyes:

I've always used AC Delco air filters with good results. I even reccomended them to my customers when I used to sell auto parts. GM spends millions of dollars in research to better their products and tests like this show that. I don't recall ever getting a return on an AC Delco air filter or spark plugs that I sold, and my customers were happy with the performance of the products. Remember the old saying, "Keep your GM car all GM."