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Ive been thinking about this for a long time after hearing that K&N filters don't flow as well as stock. So...I rigged up my mercury gauges to a box and tried it out. For those interested (and not likely to beat me up over it), the K&N does flow better as the vacuum signal was much lower. Yes, these are just showing the setup and I had the filters secured with the bottom of the air-box when testing to ensure a good seal.
I remember an old Rennlist thread and the problem with K&N wasn't lack of flow, it was particles getting through. I think there was discussion about the affect of the filter oil on the MAF too.
Bugatti Veyrons use the same exact filter as the 928. The stock filter. If the K & N was a superior filter, wouldn't it make sense that Bugatti would be using them?
Many years ago we dyno tested my oldest Strosek car a 4,7L S2 Euro. We could not see a difference in engine power between the stock vs. the K&N air filter.
Åke
yes, the oil is not good for the MAF , can ruin it. Of course no problem with CIS cars.
I just replaced a K&N with a oem. I had the problem that the border sandwiched between the air boxes is not thick enough , so the straps were "loose" .. oem is thicker and fits better.
Cool test. The analysis of your results are most likely correct, but are not definitive. You need to have a complete understanding of the flow characteristics (performance) of your source (shop vac). Take a look at the attached curve (upper one); it is the performance curve of a high performance Aerospace fan. Note at 10 CFM, the static pressure (pressure drop) is lower then when it is flowing 20 CFM. Your shop vac may have a similarly shaped curve, so knowing where on it you are operating is important.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Many years ago we dyno tested my oldest Strosek car a 4,7L S2 Euro. We could not see a difference in engine power between the stock vs. the K&N air filter.
Åke
This——^ X 928,000.
I did a dyno test 20 years ago with the K&N and stock filter: no statistically significant difference between the two.
IIRC, Louie Ott did dyno tests and lost power with the K&N.
There is basically no good reason to mount a K&N. And nobody ever f#$%ing cleans them anyway.
Just recently the Project Farm YouTube channel did a comparison test video of a number of air filters, including a K&N filter.
His finding was that the Wix and Purolator filters had the highest filtration, but also the most restriction.
A long time ago I had a K&N because I drove off road 4x4s and it was supposed to be the best. Then got a 944 Turbo and continued using K&N from it's off-road recommendations. Then got a 928GT so put a K&N on it. After a month I heard the K&N let lots of dust thru. So, opened the filter box and looked under the filter. The bottom (intake side) was coated with a very fine dust. Immediately cleaned it and replaced K&N with a stock filter. Have never had dust under the filter again.
When using K&N on the 951 cleaned and re-oiled it. Was very difficult oil the filter without getting too much oil and fouling the MAF.
Just recently the Project Farm YouTube channel did a comparison test video of a number of air filters, including a K&N filter.
His finding was that the Wix and Purolator filters had the highest filtration, but also the most restriction. Video linked here
And more importantly, the K&N let in the highest amount of particulate matter.
03-24-2020, 12:46 PM
K&N vs stock
