Smudo

My 951 is driven on weekend from spring to autumn and sees a track days a couple of times per year. Engine wise it has some slight modifications, with improved K26/6 and running standalone engine management (thus AFM is replaced with SS tube). Due to various reasons I need to retain the original airbox (I put new one last year as the original was in bad shape). As I am running 1.15 bar or around 17 psi of boost, I would like to reduce the intake restrictions and improve turbo spool-up by changing the original air filter with K&N original replacement filter (PN 33-2081). Does anyone have any experiance with those and would like to share?

MAGK944

Smudo

Thanks for the feedback. When referring to throwing oil in the intake, are you talking to the oil that is in the filter for filtering purposes? Should we worry about that at all, considering that the filter is before the turbo and you also get some oil usually from the turbo to the intercooler that goes also to the intake?I am more worried about the filtering capabilities, but they say, that it fulfills the OEM specs (if maintained properly). I know that many run cone filters, that are even more exposed?

MAGK944

V2Rocket

if your ECU runs a MAF (hot wire) sensor, a K&N will lead you to many trips home on a tow truck.

ask me how i know.

If MAP, you'd be OK, but the stock paper filter is cheap and works just fine.

Smudo

I have MAP sensor, thus the filter oil should not do any harm. Has anyone made back to back comparisons with original air filter box and original vs K&N replacement filter. If I will order it, I might try to do it.

V2Rocket

maybe apples to oranges but Rogue did back to back testing on a 944 NA on a dyno with stock paper, K&N, and no filter at all and saw 0 difference in output whatsoever.

H.F.B.

And my VEMS MAP WOT reading saw exactly 0 difference between stock paper and K&N filter.

mj951

I've been running the factory airbox and a K&N filter for over ten years without issue.

MAGK944

mj951

It suggests the K&N filter won't do harm to our engines, or at least it hasn't to mine in the past 10 years.
I've never compared air filters from a performance point of view but the OP might be more comfortable knowing others are using the K&N without issue.
I know i would. Just as i appreciated your feedback on Bridgestone tires even though it didn't answer my specific question.

I often wonder why people point fingers but I guess we each have our concerns.

Droops83

I'll weigh in on this subject with my experience in the matter.

I work at a Porsche/BMW repair shop, and about a dozen years ago we started seeing a spate of MAF sensor failures in Boxster and 996 cars. The common denominator at the time was that all had aftermarket K&N air filters.

The reason that K&N air filters flow better than paper filters is that they don't filter as well; the oil is needed to make finer particles stick rather than pass through the filter media. K&N swears up and down that their filter/oil system doesn't affect MAF sensor wires if applied properly. It is true that the customers in question may have over-oiled their filters, or applied the oil to the wrong side, but it was a common failure mode at one point, so we replaced all with paper filters at the time.

In subsequent years, we learned that the particular type of MAF sensor used in the 986/996 (Bosch HFM5 I believe) was particularly prone to contamination of the wires from oil and other debris from the crankcase ventilation system. The wires become coated and thus insulated from the passing air mass, which causes them to over-estimate airflow at idle/part load (the heated wires don't cool down quickly enough after throttle is closed) and under-estimate airflow at higher load (the insulating layer causes the wires to not cool down enough when there is a lot of mass airflow). So, we have replaced many more of the same type of MAF sensors for the same reason, different cause.

Bosch later redesigned their MAF sensors to be much less prone to wire contamination, but even these ones can fail in different ways.

I'm not sure what exact types of MAF sensors are being used in past and current 951 MAF kits, but the above is something to consider. However, there are a number of companies that make dry high-flow filters which require no oil.

As for me, I now have a VEMS system which uses speed-density/MAP for airflow calculation, and I adapted the factory airbox (with a paper filter) to keep things looking original and to ensure lower intake air temps (this is probably causing a restriction for my new K27 hybrid turbo setup, but that's a different story

RonD.

I know the argument that when using the stock AFM with factory airbox and snorkle vs the Lindsey Racing Air Filter kit air intake temps should be lower but obviously more restrictive. So, Is any body running the LR type set-up and getting any notable
gains in performance? I prefer to and currently use stock set-up for aesthetics. I'm asking because I recently did some slight mods Super 48, Custom chip, Headers( cracked stock manifold), Full 3" no cat, Dual port WG, 3Bar, stock injectors, etc. I know this is old school stuff but that's ok with me car definitely performs a lot better. Just trying to optimize.