Originally Posted by otto457

Check out the ISO 5011 tests for most any oiled air filter. I'll just use S&B's data for their filters as an example. Even they concede that their oiled filters don't do as good of job filtering as the stock paper or their dry filter. As far as the a/f ratios go, whenever the MAF environment is changed there is a chance a/f will be skewed. This mainly affects the slot style MAF in the newer trucks, but even the 2v motors can run lean due to MAF placement.
I worked in an SAE testing site for years, so it's not a problem for me backing my claims I'm use to it.