Originally Posted by Petza914

Great test.

For various reasons, I've ended up running K&N air filters in all my cars.

• 928 - custom through fender custom intake into carbon fiber airbox that mates to the supercharger
• RUF 997 (60k miles running this intake since 30k) - electric active aero rear spoiler that doesn't leave room for the stock airbox where the spoiler rams come down into the engine bay and with the supercharger and exhaust setup on this car, the increased flow of the K&N intake filter actually makes a difference at high RPM
• Other 997 (105k miles running this intake since 40k miles) - Evolution Motorsports intake with K&N oiled filter for the Twin Turbo active aero rear spoiler that's on that car too - same problem with ram clearance but those are hydraulic
• Cayenne TTS (45k miles running this intake since 35k miles) - lots on intake, exhaust, boost mods and a tune where the filters improve performance
• 914 (who knows how many miles) - runs dual 48mm carbs so have to be those types of filters
• BMW X5 (95k miles running this filter since 90k miles) - needed a new filter - why not based on my history with these types of filters - buy one once and keep it maintained like the rest of them
• GMC pickup (195k miles owned since new and running this intake the entire time) - has K&N full intake instead of the stock airbox - just because

I have never replaced a MAF in any of these cars.

There are no issues with using a properly maintained K&N filter, and by properly maintained I mean correctly cleaned and reoiled, and not over oiled. I run a Used Oil Analysis on all my oil changes and have never had a Silicon (dirt) content ppm rating above single digits. The intake on my supercharged 997 is off right now and there was no dust lining the intake piping. The secret is to stuff and wrap the filter after oiling it with a lot of paper towels so the paper towels absorb any excess oil that isn't well captured by the gauze filter media. This excess oil is what contaminates the MAF wires.

As an example, here's a UOA history I have a photo of from the Normally Aspirated 997 since it has a full history filling the page where you can see the silicon levels over a 25,000 mile period using an oiled K&N filter.






Honestly, with these filters, I likely clean them more often than I'd change a replaceable paper filter, just because I'm under the hood and decide that now is a good time to freshen up the filter. I bet on average they get cleaned and reoiled every 15,000-20,000 miles. In the cylinder style filters where they are exposed I use a K&N Hydrophobic prefilter on them that sheds any water instead of it letting it soak into the filter media. This improves the filtering efficiency and prolongs the filter cleaning interval vs. leaving them exposed to the rain.

In the 997 forum, user "gasongasoff" did a scientific study with a Fabspeed CAI on a 997. He tracked MAF values to see if the car would perform any better with the K&N intake vs the stock airbox. The theory was that if the MAF readings were higher where the car was supplying more fuel because it as flowing more air, that the performance was increased, providing the car maintains the proper AFR, which the 997 does automatically via the DME, which when you think about it makes perfect sense. That thread is here for anyone interested - https://rennlist.com/forums/997-foru...surements.html

For 928 content, here's the custom intake I have on my 928 with CF airbox and 4" fender inlet


Passenger side Fender Inlet with Hydrophobic screen. Radiator for Heat Exchanger lives here too.

CF airbox with oiled K&N filter enclosed for a true cold air intake to the supercharger

Originally Posted by WALTSTAR

I am impressed & like your style in craftsmanship and informational backup.
The reason to keep coming back to Rennlist.
Thanks again.