K&N Air Filters: Performance & Quality

Here's something else about air filters. I installed a panel filter from K&N in my VW T4 TDI (111 kW). It's been running with it for about a year now. So far, there have been no problems. There hasn't been any change in performance, which I didn't expect. However, the turbo responds faster, and most importantly, it hardly produces any soot when accelerating at full throttle. I think that alone makes it worthwhile. Also, electrostatic filtration should be finer. At our company, we have a special vacuum cleaner, or rather, a cleaner, which is equipped with a single-layer electrostatic filter. Even the finest dust from the workshop doesn't reach the filter holder/air outlet.
"I also have a K&N filter in my 1.8 A3. Now, it reaches its maximum RPM about 400 RPM earlier, and it revs freely all the way to the limiter. Before, there wasn't much happening below 3300 RPM, and above 5000 RPM, it didn't want to rev much higher. What do you think about that? I'd be interested to hear your opinions. CIAO DAVID"

Hello, I mean, if your old air filters are dirty, it's clear that a new panel filter is better. Otherwise, I refer you to the article "Comparison of paper air filters vs. fabric air filters."
If you've already read this, I'm wondering what else you want to know?

Best regards, Rainer.

. . . what long-term effects advertising and similar things can have (don't take it personally, David - especially if you hadn't read the technical article before your post ).

Even though Rainer's test article is not "scientifically proven," it clearly indicates the basic trend, which is that "nothing significant is happening."

But somewhere in the subconscious, the slogans about increased performance, the images of beautiful girls, etc., still have an effect... pleasant ideas and their associated thoughts tend to stick around in the mind very stubbornly.

The theoretical reasons why changing the air filter in a TDI engine might not make much (or any) difference are actually quite straightforward.

A different air filter doesn't increase the amount of air being drawn in (which is determined by engine displacement and boost pressure, naturally dependent on RPM), but rather improves the filling of the cylinders. However, in turbocharged engines (of any type), this filling is almost entirely determined by the turbocharger and its pressure. Therefore, a different filter can't make much of a difference.

The only advantage is the reduced maintenance, and in non-VTG TDI engines, a slightly better response in the low-speed range where the turbocharger hasn't yet built up much pressure, effectively operating in 'naturally aspirated' mode (simplified). In that range, the filter improves the air intake slightly. However, with VTG TDI engines, the difference is barely noticeable.

Reiner's values are very interesting; they essentially confirm the statements.

Best regards,

Hello,

The values also don't change within the suction range of my TDI.
For those interested: The measurements include data from engines without any air filter at all. Therefore, everyone can check for themselves how much, and whether a fabric air filter might cause the turbocharger to engage earlier. -> NO change.

Best regards, Rainer.

I believe that in the case of the AFN engine, there is no change in the suction range. The engine speed at which the turbocharger kicks in is significantly lower than, for example, in the 1Z engine. For the filter and its effectiveness, the flow rate and thus the engine speed (without turbocharger boost) are naturally important.

. . .. it seems that "sports" filters don't really offer any benefits.

Docter wrote:

The only advantage is the maintenance, and in non-VTG TDI engines, the better response in the area where the turbocharger has not yet built up much pressure, and is therefore operating in "naturally aspirated" mode (simplified). In that area, the filter improves the filling process slightly, as mentioned above. However, with VTG TDI engines, you hardly notice any difference.

Rainer also also performed an idle measurement, which definitely showed no boost pressure being generated.

At a resolution of approximately 2% of the measured value, I believe that significant differences should also be noticeable at idle, especially since a diesel engine does not have a throttle valve and already receives a "full" cylinder charge at idle (although I would describe the load operation as an "overfilled" charge *g*).
Therefore, a better cylinder filling before the loader starts up (which already begins just above idle) is, in my opinion, likely just wishful thinking...

I also doubt that there's anything fundamentally different to measure in naturally aspirated engines: while they may rev higher under full load, they only achieve a full cylinder charge, not an "overfilled" one.
Therefore, despite having approximately 50% higher RPM for the same displacement, its airflow is likely still significantly lower than that of a TDI engine with around 1 bar of boost pressure.

@Docter: Please don't take my second complaint today personally .

@Ulf: I don't have a problem with that .

However, in some areas of the vacuum system, the engine is charged by resonance (1.1 bar absolute) (TDI 2 bar absolute). Of course, this is not comparable.
However, when considering the absolute amount of air, the differences become smaller.
However, with vacuum cleaners, the filling of the cylinders is more important, and noticeable effects can definitely be observed!

All in all, I agree with you... these filters, whether here or there, don't really achieve a significant performance improvement.

Hi Doc.

Quote:

With a vacuum cleaner, however, the filling of the cylinders is more important, and such effects can definitely be noticed!

. . . that is to say, if there are significant differences in the flow resistance of different filters, Otto engines will be more sensitive to them than TDIs.

--> Ladies and Gentlemen, we proudly present:

The diesel mechanic's insider tip for gasoline engines is Rainer's used standard paper air filter!
I'm laughing my head off .

But please don't confuse the filling with the amount/mass of air drawn in. These are not necessarily the same thing.

In a naturally aspirated engine, the motor has to work less to draw in the air, while the amount/mass of air can be the same.

Hello everyone, aviation enthusiasts!
So, I have somewhat mixed feelings after reading your responses.
'With Klaro, the filling depends on the boost pressure, which is not the case with Turos.'
However, the advantage is that the boost pressure becomes available much earlier, which significantly reduces turbo lag!
However, replacement filters don't really make much of a difference, because a chain is only as strong as its weakest link.
The problem is actually the connection to the air filter.
What's the point of a filter that can let a lot of air through if not enough air actually reaches it?
'Open filters,' also known as 'mushroom filters,' can provide a solution.
There's even one now that's available with the necessary approval for TDI engines!
Furthermore, the airflow can be designed so that it only draws in cold air and not, for example, warm air from the engine compartment!

In this sense, breathe well!

I'm sorry, but that's not true at all.

An open vent = warm air = performance loss in any case!

Using an open air filter also changes the length of the intake path (which is less important for turbocharged engines), allows more dirt to be drawn in, and so on. Performance tests on naturally aspirated engines even showed a noticeable decrease in power with an open air filter!

Wenn du willst das der offene Filter nur! Kalte Luft bekommt musst du den komplett abschirmen und die Luft von außen holen! Wo ist dann der Unterschied zum Filterkastensystem? Das hat aber noch eine Art Puffer Funktion! Sonst ist es das gleiche! Also kein Unterschied zum Tauschfilter im org. Box.

And as I already mentioned, a higher fill level doesn't necessarily mean more air (because a different filter might not draw in more air!). And the fill level itself is changed by the filter, and that's the point that could affect performance!

Please also refer to Reiner's measurements for more information.

I also don't believe in a noticeably earlier boost pressure (see also Reiners' measurements). The boost pressure is determined by two factors: the exhaust gas flow and the resistance required to compress the air for the turbocharger's speed. How much difference does a slightly lower flow resistance make in compressing the air to 1 bar? And what if there's less exhaust gas flow available?

Hello Doc,
You are right about the shielding, and that is indeed the case even with the TÜV-approved version.
Around the entire filter is an aluminum housing.
You can attach a hose to this housing and then install it inside the radiator grille in such a way that it only draws in cold air.
Furthermore, while riding, you experience wind pressure on the tire, similar to the 'ram-air system' found on some Kawasaki models, or the well-known 'Ari-in-take' used on the Golf 3.
'Klaro' might get dirty faster because of the filter, but it's washable, and besides, dirty filters are still the best!!

Sure, here is the translation of the text from German to English:

'Hello'

Hi.

Quote:

Around the entire filter is an aluminum housing. You can attach a hose to this housing and, by doing so, install it from the inside into the radiator grille, ensuring that only cold air is drawn in.

Indeed, a great thing... What do you think, why are coolers, among other things, also made of aluminum? Because it's not only lightweight, but also allows heat to "pass through" quite well.

What does this mean for the (presumably also lightweight = thin-walled) filter housing? That heat from the engine compartment easily seeps through the housing, and the cold air, which is already laboriously drawn through the long hose, is warmed up again.
Simply brilliant, roughly the logical counterpart to LLK --> an SLH = supercharged air heater .
While it might be less effective than a liquid cooling system due to the presumably smaller heat exchange surface area, if we're already discussing individual degrees of cooling performance, I think we should also consider the purpose (??) of an aluminum air filter housing.

--> Those who want to keep the intake air as cool as possible , probably have no choice but to wrap old towels, corrugated cardboard, or anything else that allows air to pass around the nice-looking(?) aluminum casing.

Even the standard plastic enclosure is significantly more practical, because any plastic is a highly effective heat barrier compared to aluminum.

Sometimes, it seems to me that there's a secret competition among the providers of "sports" LED lights, etc., to see who can make the most money with the most blatant disregard for basic physics .
Was ihnen durch die Augen-Orientiertheit des Durschnittskunden auch recht leicht gemacht wird: "Aluteile im Motorraum, boah ey, Renn-Optik! "Sold, man!"

That reminds me of a riddle I heard recently:
Why should women be more likely to be pretty than intelligent?
Because men are better at observing than at thinking.

I hope I haven't offended too many people.

Okay, a sports air filter definitely makes sense! But most people here probably won't agree with that.

Okay, I need to elaborate a bit to make this understandable:



For example, in classic tuning, the channels are polished.
Why? To reduce the resistance of the flowing medium (in this case, air) against the channels in the intake manifold. Therefore, the engine has to do less work when drawing in a specific amount of air!


What does a sports air filter do? Have you ever breathed through a 'normal' air filter and then through a sports air filter?
Right, with the 'normal' version, the air flows back!
Why? Because the drag is lower!

Did you notice anything in common with the text above?


By reducing air friction during intake, the amount of work the engine has to do during intake is reduced. This increases the thermal efficiency and, consequently, improves the overall efficiency.


The increase in performance is there, but it's so minimal that it's not noticeable. But it's there, even if it's only 2 horsepower. Usually, it's more. I drive a Polo SDI (a naturally aspirated engine), and after installing a K&N filter, the fuel consumption decreased by about 0.5 liters per 100 km. There was no noticeable increase in performance. However, since that seemed strange to me, I reinstalled the old, cleaned filter, and the fuel consumption increased again by the aforementioned 0.5 liters. So, there's definitely something to it! I don't know how it behaves with a turbo, but it's probably similar. Has anyone tested this? (someone who is unbiased)


Best regards,
Ingo

ulf wrote:

Sometimes it seems to me that there is a secret competition among the providers of "sports" drones, etc., to see who can make the most money with the greatest amount of physical nonsense.

Okay Ulf, I'm giving up... From now on, I will no longer answer any further questions on this topic, and will only refer to the relevant article.

@Ingo: With a fabric air filter, the cylinder fill level remains the same in both naturally aspirated and turbocharged engines.
At the speeds used in the article, it is clear that without the use of the turbocharger, the amount of air drawn in per piston stroke, and thus the volumetric efficiency, remains approximately the same.
To check whether significant changes in the power consumption of the turbocharger occur at very high air mass flow rates, the Ulfsche flow test was performed three times for each filter used. The measured times remained within the measurement tolerance.
With the basic values of the ventilation calculator, a 2% change in performance results in a time difference of approximately 0.15 seconds.
This time difference was not measured, so the performance difference is significantly less than 2%, which in my case is less than 2kW.
Again: Don't compare apples and oranges. Anyone who compares a paper filter that has been glued in with a freshly cleaned fabric filter, or vice versa, can always influence the result to suit their own desires.
Die Ausgangsbedingungen müssen schon gleich sein, da mein Gewebefilter gerade mal 6.000km gelaufen war, müßte er bei den Tests ja wenigstens genausogut abschneiden wie der 12.000km Papierfilter. HaHe didn't do that, though.

I am closing this topic.

Best regards, Rainer.