Visual proof of the importance of air filters. Back in 2017, I purchased and installed a UPD kit that installed a spacer in the air filter box to lift the air filter elements out of the air flow intake to improve air flow and horsepower. The kit came with the "oiled cotton gauze sandwiched between two layers of metal mesh" so I went with those filters. A little over five years and 91,000 miles later, when performing a maintenance service, I noted the cotton gauze filter elements were literally disintegrating. I pulled the filters and installed MB paper filters. This past week I was reworking the supercharger on my car and got a look at the compressor rotors. I will never install a "cotton gauze sandwiched between two metal mesh" filter again on anything I own.

 

Do you think the marks were caused by the cotton "gauze" or some of the metal mesh?

 

Metal mesh was fine. My hypothesis is particulates were adhered to the oiled cotton gauze and, when the gauze fell apart, the cotton and particulates were pulled through the supercharger.

 

Those sort of air filters are garbage, and have always been garbage. Use them when you would like the air filter to allow debris into the engine. Every time I service an oiled filter, the downstream air tract is filled with dust.

 

Years ago there was a guy who raced a Porsche 944 turbo, he used K@N filters and had to rebuild his engine frequently. Someone pointed out it was probably due to his air filters. The guy said to take a dab of bearing grease and put it behind the filters and see what you find in the grease. He did and he found small gritty particles. At the end of the season he rebuilt his engine put paper filters back in the car and only had to rebuild his engine after the full race season. Use stock filters.