Speedtoys

And..a restriction (pressure drop) only matters if your air needs are at that point where you need the test flow, etc.

WALTSTAR

I did the swap because while doing my engine check, I found full leaves under the stock filter and couldn't figure out how they got there. has anyone else had this happen? Guess I will just have to check more. Stock goes back in.

Speedtoys

You thought the stock filter let the leaves..through so the K&N would do better?

worf928

Large debris under the filter is due to not correctly seating the upper air box section with the filter and lower air box section. (This, assuming the straps are actually present and clipped...)

Or just not cleaning it out to start with. I've seen both.

worf928

Feel free to copy the URL and add it to a bookmark. It ain't like I didn't steal it from teh interwebs this morning. I had another one but wasn't available on my ipad:

Bmw635

Remember the MAF on 928 is NLA and the oiled K&N failed the MAF in mu car so I had it rebuilt. Same problem on my Supercharge E38 fouling the Bosch MAF- had to replace new MAF after 10K miles.

SeanR

HuH?

WALTSTAR

I didn't swap the filter as a result of the leaves (although I didn't want them in the cavity). I changed the filter as a WYIT thing when checking the engine and fluids.
Why do some people attempt to make others look stupid? The only reason to stay is for the communication with more reasonable persons.

worf928

I assume you refer to me. I'm not trying to make you look stupid. You asked a question. I didn't assume that you were involved in getting leaves under the filter. I answered based upon what I've observed with 928s brought to me.

There is (at least) one other way that leaves can get under the filter: one or both halves of the air box is warped (at the rear) and thus making it difficult or impossible for the filter to seat well no matter what. This I have also seen a couple of times. It is actually not difficult to accidentally mis-seat the upper half of the air box such that the filter isn't seated. If the air box stand-offs are bent such that the rear of the airbox is touching the firewall then it's even easier to get the upper lid mis-seated.

Mrmerlin

OR as i have noticed when removing the top half of the housing the rear edge of the filter comes free and the big parts drop into the lower half.
I just scuttled another KnN the other day , the whole lower housing was filled with micro dirt particles all of this was going right into the engine.

Bigfoot928

stock air filter usually is not a bottleneck. I was sucking the factory intake tubes flat on the dyno... with a factory air filter.

Speedtoys

No he meant me.

After all, the only reason he tied changing filters was that leaves got under the stock one...

I just made the jump given the information I was left with. If there was another reason _it was not mentioned_.

GIGO

WALTSTAR

Wrong again. Perhaps the way it was written led you to believe that I thought that the stock filter had voids large enough the allow leaves to enter and the K&N didn't. In fact, I had the K&N at hand and decided to change it out (not as a response to the leaves, specifically) since I wanted to test the flow for some time. At least you are cognizant of the insinuation... For future record, I am no dummy. I have written my own patents and engineered earthquake resistant structures among other things. I have engineered and built several models that reside in New York and Pennsylvania museums. I do understand dynamics and statics, so no, I wouldn't believe in the "leaf through the paper trick".

WALTSTAR

Worf928...No sir, not you.

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