Performance Filters - Not always the best option
 

I thought I would post up this little piece of info, as I thought some of you would be interested.

As you know I also now have the Leon K1 and the 1st little modification was to be the obligatory K&N Panel Filter. Primarily due to a pending Revo session where they recommend a performance panel filter (although one of their own).

I wasn't sure whether to go for an ITG/VWR, Green or K&N. I was keen on the Green as I know they flow well from experiences in the Subaru world.

However, a new K&N popped up so I grabbed that knowing that you can't go far wrong with a K&N.....or so I thought.

The filter was fitted last week, and it's not such and easy job. On the 2.0TFSi EA113 engine it is located inside the engine cover. So it requires disconnection from the air intake, disconnection from the turbo intake, removal of MAF connection and complete removal from the car (engine cover is held tight on rubber mounts). You then have to break open the engine cover with about 10 captivated self-tappers.

So K&N fitted, sticker applied and I thought all would be good.

Over this last week, when it has had the opportunity for a quick squirt it just didn't seem to have quite the same pull.
A quick diagnosis with the Torque Pro App lead me to get the Laptop out and log with VCDS.

Although this was reporting that actual boost was tracking specified boost (as close as any other logs I have seen from other owners), the MAF Airflow G/S seemed low, as I had seen people report this should be 190 (ish). I was only seeing it pegging at 170G/S.

So is this K&N over oiled ????

I have since replace the OE paper filter and re-logged.
The car now feel back to where it was and the MAF is reading anywhere between 187-191G/S.

So the supposed 'Performance' Filter actually flows less than the OE paper filter.

If you use the G/S - BHP Conversion rule of G/S divided by 0.8, this actually equates to a loss of 26BHP (more than a 10% drop). Hence what I could feel (I assume)

170/0.8 = 212BHP
191/0.8 = 238BHP

Car is specified as 240PS which is 236BHP, so it looks to be performing as expected.

I had read a bit previous to Subaru ownership about the oil on a K&N sometimes upsetting the MAF, not just because of the flow issue as you may have stumbled across but also the oil itself being drawn onto the MAF sensor and hindering its ability to measure air flow.

I was always surprised that such a well known and trusted product had such reported ill affects.

I used a Pipercross filter in my Leon R as no oiling was required but I currently have a K&N in the Scoob and have considered changing it out for a while, I might be looking to do this now sooner rather then later!


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I always rated K&N, but TBH I had a Green in the Scoob when it ran the OE Airbox.
That flowed a lot better than my previous JDM STi paper filter, as the Injector duty shot up by about 4% to cope with the extra airflow.

The K&N in the K1 was new and was sealed in the box. The plastic bag it was in did have some oil in the corner.

ITG used to be quite bad for Scoobs as they would pool oil in the corner of the airbox. I think it was these that started the whole MAF killing rumour, although the MAF's are pretty fragile anyway.

I've heard plenty of bad reports of K&N filters, so this isn't a big surprise.

Interesting to see it was so noticeable though.

Good right up Scott,
Personally I wouldn't use an oiled filter in maff cars such as a scoob , there weak as it is,
But it's very interesting to say what you have logged ,
So what will you run now? I like the cosworth stuff, used in couple of my scoobs,

Be worth writing to K&N Scott with your findings and see what they have to say for themselves, I'm guessing over oiled from factory.

I've personally never had issue with K&N filters on mine in the last 7 years, on the current one or the panel one I had before in classic and newage (both cone and panel), but I've not over oiled it, and always removed any excess oil after wicking is complete etc.

I have a do-luck foam panel one somewhere that came with masses of oil on it, but was supposedly the highest flowing filter available for a standard airbox, I was not convinced!


Certain Subaru models have been known to have weak MAFs others are known to be better, v5/6 classic for example are prone to failure,

I have a Cosworth filter which has been excellent.

Used a green in wagon, no probs, hks foam in rb5 no probs.
K&n on golf r32 cai, issues, lack of power etc, stuck hks from Evo 7 on golf cai, no probs.
K&n in my modded Audi, 57i kit, sucked itself almost inside out loosing 50+ bhp when running around 300bhp.

I Agree,i have been running K&N filters since I was pushing up my Renault 5 turbo 20 years ago now and have never had no problems with them,but I do agree that over oiled filters can cause havoc with the MAF sensor on Impreza's and usually that is the problem. You should still contact K&N with your findings,as really for a performance air filter,a brake horsepower lost of that magnitude is not good enough.SJ.

Not good results for the K+n so just ordered a cossie one and time for a change,thanks for posting up results

my opinion is that oil impregnated cotton filters are good when no maf or a maf far upstream of filter and not turbo'd. hence oil shouldn't hit maf. these filters have good filtering abilities.

foam filters, high flow, no oil to worry about, but not as good at filtering.

that saying, jo has no filters on her twin 45'd pinto in the 7, and so what if engine lasts only 50k miles, quick rebuild and away we go again.

To add to tha above review/performance of the K&N panel.
As you will of read from the above the K&N didn't perform too well when compared to the OE paper filter.
Well, I thought I would give it another go so threw it back in over Christmas and clocked up a few more mile on it with a run up to the folks. It's probably done about 800 miles now, so it was time for a touch more logging.

The MAF g/s are now reading high 170's / low 180's (i.e 181). Whereas the OE paper filter is reading high 180's with the odd flicker to 191.
So after 800 miles I assume a bit of oil has been pulled through the K&N and freed up another 10 or so g/s. But the OE paper filter is still outperforming it.
The g/s BHP maths work this out to be about a 12BHP variance.
So the OE has gone back in, in preparation for an R-Tech remap in a month or so.

Have you thought about trying a cosworth filter as there dry flow?

Green cotton filters are meant to be good never used them just what ive heard .