PaulCarrera

84 928 S2 euro
Just about to change my air filter and I can get a normal one or I can go for a K & N one that is supposed to be better air flow but also cleanable for twice the price so wondering if they are really any better and if you can really clean and reuse them. Anybody with any experience of using them?

Also I have come across the pipercross washable foam ones that sound good for a little less than the K & N with lifetime warranty

hacker-pschorr

Stock, easy to find and they work.

After you've taken out a number of K&N filters only to find debris on the MAF screen, you realize they let more dirt through.

I won't even go into the controversy of the K&N oil killing the MAF hot wire.

Speedtoys

Unless youre over 700Hp, stock filter works fine, and filters 10x better than a K&N dirtflow.

PaulCarrera

thanks guys I will stick to stock then

OTR18WHEELER

...just make sure you don't install the original spec filter upside down, ...it's as bad as not knowing you are missing the jump post cover.

The Forgotten On

^^ for most others, it causes it to run lean.

Speedtoys

Which makes no sense.

Its not a carb/jetted engine.

OTR18WHEELER

I don't think the k&n causes a lean condition, it will allow more air through though.,....wait a minute, that would cause a lean mixture.

hacker-pschorr

The paltry amount of additional air possibly allowed through by a K&N filter is well within the operating range of the air meter from any year 928. If these cars had that narrow of an operating range, you couldn't drive from death valley to Pikes Peak without re-tuning the engine.

The Forgotten On

It's the hump of the air filter that prevents air flow if flipped the wrong direction

jcorenman

The MAF meters airflow, whatever it is, so a restrictive filter or high altitude won't change the air/fuel mixture: less air means less fuel.

Where things do get messed up is that the MAF only measures airflow in the little venturi gizmo, in the central 1" or so of the MAF housing. If the flow is uniform across the whole MAF then this central measurement is an accurate estimate of the total airflow. And uniform airflow requires some plenum volume upstream of the MAF, so that the air has a chance to settle down and flow smoothly.

Which is Blake's point, and is exactly right-- the hump in the filter does reduce the "headroom" above the MAF intake, which does restrict the airflow to a degree. But it also messes up the distribution of that air flowing through the MAF. If the flow is now weaker in the center then the MAF will under-estimate airflow and reduce fuel to match, which results a weak mixture.

Bottom line: Do it like the factory did it, stock filter and right-side up... Or change it completely (velocity stacks through the hood?) and re-tune.

Mrmerlin

I have a brand new KnN filter that came on my 80 Euro 5 speed,
I was going to give it away.
Doh thats not nice ,
I will just stick it in the trash
lots of little stones under the new filter, musta leaked around the edges

corellian vette

OK now you have me questioning - which IS the proper way to mount the air filter? There were no markings on the one I got - and the look like they fit either way.

In my case, the Flat part is facing DOWN (towards MAF) and the HUMP is facing up. Did I get it right?

skpyle

Stan, that's what I did with mine...

Speedtoys

Yup!