Is there really going to be a big difference between a K&N and any other aftermarket cotton fiber type air filter? (Here is a link to an e-bay auction of a similar type of filter that I am referring to)
http://cgi.ebay.com/ebaymotors/Ford-...36498155QQrdZ1

I am not looking to buy one of these $4 filters but I am wondering what makes people say that the K&N is so much better than any other air filter when I have never noticed a difference with one (on my Mustang GT at least). Realistically, I am thinking the difference may be some but not to a point where it is going to hurt performance over the stock intake set-up.

Your truck will only suck up as much air as it needs, regardless of what filter you have on it (stock, K&N, Cotton Fiber, etc...), right?

Also, is anyone aware of this study regarding air filters?

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

 

That filter on ebay looks like an S&B. S&B makes filters for many of the different aftermarket intake kits, including Air Force One

http://www.sbfilters.net/

here's an AF1 filter made by S&B

 

Results will vary with the vehicle that the air filter is installed in. Improvement in a Mustang GT won't be as noticeable as in a Taurus. I had a K&N filter in my '99 V-6 and I noticed better throttle response rather than harder acceleration or more horsepower. Probably the best benefit is that they help reduce turbulence that can create restrictions in the intake snorkel.