I found the link to this study on a Lincoln Town Car forum:

Air Filter Comparison Study

While it was done using air filters for a GM Truck, the conclusions are interesting:

1. choosing a filter type or style for ‘more flow’ for either performance or fuel mileage is useless, as they all flow about the same

2. there is a wide variance in the ability to filter contaminants; the best was an unoiled synthetic fiber passing less than 1% of the contaminants introduced, while the worst was an oiled foam allowing 40% to pass. To bring in some 914 relevance, the K&N was second-worst, passing 35%.

I make no claim that this applies directly to our 914s, but I found it interesting since I've always used K&N filters on my performance cars.

That study or test is not surprising, & there are a few others out there coming to the same conclusions.

My long time 914 Porsche Mechanic (he trained on them in `69) had said the same thing about K&N & the other suppusedly "higher flow" air filters - they don't add appreciably more air flow, but do add significantly larger particulates into the engine & systems due to the more porous filter material.

He said flat out not to use them - & instead use a very good quality OEM 914 filter (or whatever make/model it is).
He said in his Austrian accent: "I haf my vays to get performance out off deze engines!"

The other thing that K&N tries to hook you on is that they're "reusable filters" - but per Hans: "Der iss no vay dat you can get dat filter completely clean!"

I've been taking my 914 & other cars to Hans since 1975, & he PPI'ed & rejected 2 dozen 914s in `75, before I got his blessing on the 73 2L I got & still have. So I trust him implicitly!


Tom
///////

More flow means more particles getting into your engine. I still remain baffled at the hotrodders who run open air intakes because they look cool. Who cares about air filters?

I understand if you break your engine down after every race.

Hello to everyone else. Put a damned air cleaner on your damned car.

When working for a company in the late 90s specific to light aircraft /experimental we ran Rotax engines and most of the filters were k&n the thing explained to us that when flying there were allot less contamination then when on the ground.. Tests showed for auto relates for k&n were horrible at that time.. I will never ever run a k&n again.. Completely a waste of money..

Makes sense at altitude. Still gotta get up there.
I hear the echo.
Do you use air filters? Birds might the biggest worry. I guess the bugs are lube.

That is classic forum crap

I see these tests on every forum there is but there are always variables not taken into consideration such as air box design, acoustic tuning of intake manifolds, and many others when it comes to flow.

A flow bench made from a used MAF sensor (and one that was known to be inaccurate even when new!) and a 5hp vacuum is useless.

Every car is different, pick up a few different filters (foam, cotton, synthetic), strap your car to a Dyno and see which one works best for you.

As far as contamination, let me know when you find a pile of 5 micron dust in your intake

I agree that the airflow test is flawed. It tells us only how the filters compare at a single vacuum pressure and we have no reference for that pressure. They didn't even report the airflow with no filter in place. I have no idea how the suction of their 5HP vacuum compares to a 914 or Lincoln at 5000 RPM. To do it right, they should have tested the filters at a range of vacuum pressures that mimic typical road and track values from idle to redline. You can imagine that filters may perform similarly at low vacuum pressures (idle) with differences increasing as the amount of suction increases.

The filtration study, OTOH, I think is very telling. Again, it would have been better with testing through a range of vacuum pressures but the fact that any filter passes 30% of 5 micron at any vacuum pressure is alarming. Correct me if I'm wrong, but I don't believe the job of an air filter is to prevent your engine from clogging with dust, but rather it is to prevent abrasive particles from running through the combustion chamber and tearing the up the engine.

When I bought my carbs over 30 years ago, I thought the K&N filters that came with them were about the coolest thing ever. But the more I looked at them, the more I realized that red stuff you spray on them is snake oil and I decided they would never be run on my car.

One of the late Captain's favorite rants.

Average particulate size for a paper filter to stop is 3-5 micron, the loosest aftermarket material is usually about 10 microns (this doesn't include steel mesh). There is a balance between filtration and flow.

Most engines don't even notice particles this small in the intake tract as they are usually soft materials unless you live near a sandy area(aka silica). These particles get wet down by fuel and burned in the combustion process without doing any harm.

The filter oil for the K&N and other brand oiled filters actually does work when applied properly. It decreases the size of particles trapped by the cotton/gauze element. If over applied it can cause issues in car with MAF sensors. In a carb car it will just suck the excess oil out and burn it with the fuel.

Like I said in my previous post, every car is different, every engine is different, do the testing with your car to see what works best for you.

NEVER take forum crap as truth unless there is actual usable data to back it up (not a vacuum cleaner!)

Yeah, I was trying to be funny with my "snake oil" comment. I do realize the oil does work, but when I gave the old eyeball test to see the pore size passing through the K&N gauze, I realized those filters were not for me. Oil or not, a lot of fine particles are going to make it through that filter. I have 3 miles of dusty dirt road between my house and the nearest pavement. Most of that fine dust is clay that contains various silicate compounds that I'd rather not suck into my engines if I can help it. The fancy filters might have their place on the race track, but for my street cars, they don't make any sense.

K&N's "fact" page on the subject sets off my BS detector. For example, they say, "Studies have shown most engine wear is caused by particles 10 to 20 microns in size." They provide no citation. So which studies show this? Is it all or at least most studies, or just a few cherry picked from studies that show otherwise? And what is "most engine wear"? That could mean 51% which leaves 49% of the wear for particles NOT targeted by their filters to cause.

I agree with you, propaganda and pseudoscience abounds on the Interwebs. Reader beware.

The best way to get the late Capt Krusty fired up was mention K&N air filters for our 914s!

Miss his knowledge and krustness.