My example of the K&N air filter is a perfect example.
One day I was actually recommending to a buddy that he get a K&N for his 928. I run (and maintain) 3 vintage front engine Porsche cars, and I had fitted two of them with the K&N. He referenced me to ex NASA engineer and tech support guy at 928 Specialists, Wally Plumley. Wally told me they no longer will sell the K&N due to "no improvement in performance" and due to oil from the filter medium getting into the MAF wire and causing problems. Upon further digging, I discovered the K&N admits more dirt, becuase the holes are bigger. Another buddy of mine suggested putting a dab of grease on the inside of the air box, behind the K&N and driving for a while. Upon seeing what was deposited on the grease (dirt) I pulled the filters off my cars and burned them both.
It turns out, the paper filter medium won't flow as well as the K&N on an inch per inch comparison, but the paper filter has so many more square inches to make up for it, the resulting end flow is about the same, and the paper pulls out a lot more dirt. I think you can see from the photo below, if you stretched out the filters flat, the paper filter would have a LOT more filter square footage, and it doesn't need to flow as well as the K&N in order to perform equally well.
(Gimme a match !)
Just another example short of the Turbinator and Slick-50 drained from the Viper that drove around Manhattan with no oil in the sump.
The kit-of-parts we're shopping for on some of these issues will DETRACT from performance if we're not careful. Many of the kids are paying upwards of $400 for those fancy cone air filters, and many of them are to be mounted BEHIND the radiator, where they suck a nice hot charge from the radiator. We all know cool air is best for performance and fuel economy, yet they seem to sell a lot of that stuff becuase it's packaged nicely!
Regards,
Paul