Verhalten hier im Forum, Luftfilter, Liefergrad | Posts 37+

davidshoes wrote:

I seem to have sparked a discussion. However, my concern was more about the filtering effect than about increasing performance (which I have actually tried myself). So, the question is whether a K&N filter cleans the air better, worse, or equally well compared to a paper filter. But please don't, because you can see through it or something like that... Perhaps someone has experienced engine problems due to contaminants, which might suggest this is the cause. Regards

It's just as good, but not for me!


Sure, that's fine.


But here's something else:

I believe that the effectiveness of textile filters is also determined by the difference in air-fuel mixture preparation and the measurement of air volume or mass.

In our family, we have equipped four vehicles with K&N filters.
1. G3, 1Z TDI 66kw series – Low mass, filter effect close to zero.
2. Lupo, 1.0L engine (37kW) chipped to 48kW – neither air mass sensor nor fuel mass sensor modified – here, the ideal air-fuel mixture is regulated based on the lambda sensor. The effect of the filter with the chip is yes (difference of 2kW on the dynamometer), without it (subjectively) no.
3. G3, ABS 1.8l 66kw, same fuel injection system as the Lupo. The effect of the filter is very slow, but the engine revs up a bit more willingly.
4. Jetta1 GLI, DX 1.8l 82kw: Everything here is non-standard, starting with the G-camshaft, the throttle body from a 5E model, the cold start valve from a 5E model, polished channels and intake manifold, and even the air mass sensor from a 1600 GTI (which does NOT lean out the mixture!). The effect of the textile filter is very noticeable!

Assuming that the K&N filter has a lower flow restriction, it is likely (as Rainer measured) that the airflow through the mass airflow sensor (MAF) is slower, which means the MAF sensor reports lower air mass values than the actual value (and consequently, less diesel is injected - resulting in less soot). Performance??)
In the older Jetta models that have a mass airflow sensor, the throttle plate is lifted higher, which results in more fuel being added.
I haven't given much thought to the Monojet (G3 ABS, Lupo ALL) yet... It should also be the case that the amount of fuel is increased.

Hi.

Here's a simple question: What does a "bad" filter do?

IMO, the only possible effect is that it creates (an unnecessarily high) resistance to the airflow.
This creates a pressure drop across the filter, analogous to the voltage drop across an electrical resistor carrying current.
The total mass flow rate (mass per unit of time) decreases, again in analogy to electrical current. Before the filter, the average flow velocity also decreases (assuming the external pressure remains constant), because this is the only way to reduce the mass flow rate.

Behind the filter, the air flows faster again, but it continues to be "thinned out," so that the air mass meter should also notice this.
At the same engine speed, ultimately, less mass of air should reach the cylinder per kilowatt.

That's exactly what Rainer measured. The result is that there are differences between the individual filters, and even some that are disadvantageous to the K+N filter.
What, in my opinion, clearly demonstrates is that the K+N filter has a slightly higher flow resistance for the A3 air filter housing compared to the used paper filter.

However, it is likely that this cannot be automatically applied to other comparisons between standard and "sport" versions of aircraft.
Perhaps the standard filter for Bertil's Jetta actually has a higher flow resistance due to its design compared to the K&N filter for the same car.

However, Rainer's sample clearly demonstrates that, at least in the A3 AHF configuration, the K+N filter offers no performance advantages.

ulf wrote:

Although the air flows faster after the filter, it continues to be "thinned out," which the air mass meter should also detect. At the same engine speed, ultimately, less mass of air should reach the cylinder per kilowatt. That's exactly what Rainer measured. The result is that there are differences between the individual filters, and even some that are disadvantageous to the K+N filter. What, in my opinion, clearly demonstrates is that the K+N filter has a slightly higher flow resistance for the A3 air filter housing compared to the used paper filter.

Hello ulf,

Given that the used air filter had the highest "air mass flow rate" in Rainer's test series (but also likely the highest flow resistance), I would say that the mass airflow sensor (MAF) is "lying" because the pressure conditions (within the MAF) do not correspond to the stock condition (new air filter).
The wire in the mass airflow sensor (MAF) is cooled too much due to the high airflow, causing the reported air mass to be too high, leading to excessive diesel injection - the result is black smoke. With K&N, it's quite the opposite.
However, this also reinforces Rainer's claim that K&N filters don't improve performance, because the amount of diesel being injected is being reduced!

...
2. Lupo, 1.0L engine (37kW) chipped to 48kW – neither air mass sensor nor fuel mass sensor modified – here, the ideal air-fuel mixture is regulated based on the lambda sensor. The effect of the filter with the chip is yes (difference of 2kW on the dynamometer), without it (subjectively) no.
3. G3, ABS 1.8l 66kw, same fuel injection system as the Lupo. The effect of the filter is very slow, but the engine revs up a bit more willingly.
4. Jetta1 GLI, DX 1.8l 82kw: Everything here is non-standard, starting with the G-camshaft, the throttle body from a 5E model, the cold start valve from a 5E model, polished channels and intake manifold, and even the air mass sensor from a 1600 GTI (which does NOT lean out the mixture!). The effect of the textile filter is very noticeable!
...


Regarding the Lupo, I'm quite certain it also has a mass airflow sensor (MAF). The Golf III definitely has an air flow or mass sensor. The 'L' system only regulates it. The fuel injection quantity is primarily determined by the amount of air. At full load, the L control system is even deactivated.

Here's the translation:

'Regarding the difference between air flow meters and mass flow meters.'

Both systems measure the air mass! This is absolutely necessary because the Otto engine requires a very specific air/fuel mixture ratio to be set (stoichiometrically 13.x kg of air per 1 kg of fuel), and only then can an accurate injection timing be determined. The mass airflow sensor (MAF) sends a signal directly indicating the air mass to the engine control unit (ECU), while the air flow meter measures the quantity of air, and the ECU additionally determines the temperature of the intake air and calculates the air mass. While this has its drawbacks, even with a mass airflow sensor, the engine control unit (ECU) can accurately determine the amount of air mass involved.


Given that the used air filter had the highest 'air mass flow rate' in Rainer's test series (but also likely the highest flow resistance), I would say that the mass airflow sensor (MAF) is 'lying' because the pressure conditions (within the MAF) do not correspond to the stock condition (new air filter).
The wire in the mass airflow sensor (MAF) is cooled too much due to the high airflow, causing the reported air mass to be too high, leading to excessive diesel injection - the result is black smoke. At K&N, it's quite the opposite.
However, this also reinforces Rainer's claim that K&N filters don't improve performance, because the amount of diesel being injected is being reduced!


I believe that too, and it explains why Otto is so thin.

...here are my own experiences regarding textile filters.

My current car (35i, 1Z):
'First, with my old JR filter from the engine bay, it was sluggish and slowly deteriorating. A paper filter was a better temporary solution, but still not great. However, with a K&N filter, my gut feeling tells me that below 2000 RPM, which is where the 1Z engine falls far behind the AFN engine, the response is noticeably more eager. There's no noticeable difference in power at higher RPMs or in fuel consumption, and the intake noise is barely audible anyway.' So, it's basically just a matter of 'I'll never buy another air filter again.'

The predecessor, the 35i, had 90 horsepower and ABS.
The JR filter was newly installed, and I also removed the throttle bodies from the top and bottom of the air filter housing. I replaced the 'Greenpeace placebo,' also known as the catalytic converter, with a nice tubular exhaust manifold from Supersprint, which conveniently had a thread for the oxygen sensor. With these two relatively simple modifications, the car was completely transformed. According to the speedometer, the top speed was about 25 km/h higher. Before, it took a lot of effort to reach 190 km/h, but afterwards, I could cover the same distance at 215 km/h (I never really cared about real-world measurements). The acceleration was significantly improved, and the most impressive thing was the fuel consumption. It was at least 2 liters less than stock! Even with extremely fast driving on the highway from Starnberg to Aachen, it uses no more than 9 liters per 100 kilometers. With a catalytic converter, it easily uses 12 liters.

My personal conclusion: it depends on the car and how the engine determines the change (it happens, regardless of what a mass airflow sensor might indicate numerically). It also depends on how the engine control unit (ECU) can handle it, meaning how much room there is in the mapping to process the increased amount of air and compensate by enriching the fuel mixture.

Which actually brings us to the next point...

In theory, any changes to the intake system in a diesel engine can only have an effect if they are accompanied by a corresponding increase in fuel delivery. The reason for this is that we talk about quantitative control (in gasoline engines) and qualitative control (in diesel engines). Quantitative control means that the engine is regulated by the amount of air it draws in, specifically through the throttle valve, and this amount of air is then mixed with fuel to achieve the ideal air-fuel ratio of Lambda 1 (14 kg of air to 1 kg of fuel). An open throttle (Luffi) is typically detected by the mass airflow sensor or the oxygen sensor. If possible, and if the engine control unit's mapping allows it, the system will attempt to compensate for it, resulting in a slight increase in power, but also potentially leading to a richer fuel mixture. In conventional systems (what we all drive...), the engine is controlled by the amount of fuel injected, and it 'draws' the amount of air needed for optimal combustion. Furthermore, in modern engines, the maximum power output above 4200 RPM is already reduced, so what's the point of more air? Technically speaking, the engine doesn't 'need' it.

Regards,

Dominique.

Docter wrote:

Okay, I'm quite sure the Lupo also has a mass airflow sensor (MAF). The Golf III definitely has an air mass meter. The "L" system only regulates it. The fuel injection quantity is primarily determined by the amount of air. At full load, the L control system is even deactivated. ...

The Lupo and the Golf III have a single-jet injection system (although it's debatable whether it can really be called an injection system), and it definitely does not have a mass airflow sensor (MAF). There's nothing before the air filter, and immediately after the air filter comes the throttle valve and the fuel injector. If you want, I can email you some pictures. I've had four cars with this Monjet engine (I still have one), and if you disconnect the oxygen sensor, it's roughly equivalent to disconnecting the NBF (Notlauf/limp-home mode) on a TDI.

Docter wrote:

... I believe that too, and that explains Otto's emaciation...

Yes, it can become lean, but the lambda control system will enrich the mixture again because the L1 value needs to be restored. I had to re-tune my Jetta with the K&N filter (using old-school methods – no engine control unit or other fancy gadgets).

Okay, I'm surprised that the Lupo has a MonoJet engine, but whatever, I don't know much about the Lupo.

What I am certain of is that both systems must work with a measurement of the air mass. It is possible that this measurement is not performed by an air mass sensor (MAF) as in a TDI engine. As I have already mentioned, there are several ways to determine the air mass, including using pressure flaps or the throttle valve angle. EVERY injection system, including single-injector systems, must use air mass as an input parameter, as this is the starting point for quantitative control.

But I'd be happy to take a look at the Bosch documentation this afternoon or evening and tell you how the MonoJet system works.

Best regards,

Okay, let's get down to business:

The Golf III with ABS does not have a MonoJet system, but rather a MonoMotronic system, and the Lupo likely has the same.

Regarding how it works:


6.2.2 The Mono-Jetronic.
The Mono-Jetronic features a central injection system located directly upstream of the throttle valve. The distribution of the air-fuel mixture occurs similarly to a carburetor. The control is electronic, and the injection is intermittent (occurring in intervals). Fuel is pumped from the electronic fuel pump to the central injection unit, where the electronics inject the fuel into the intake manifold. This is controlled by a control unit that processes and evaluates data such as intake air mass, engine speed, engine temperature, intake air temperature, lambda sensor signal, throttle valve position, and battery voltage. When preparing the mixture, the goal is always to achieve an optimal fuel-to-air ratio, regardless of the operating conditions. This type of central fuel injection is still occasionally found in small cars and in weak, large-displacement American six- and eight-cylinder engines.

6.2.5 The Motronic.
The Motronic is the current state of development. It combines fuel injection and ignition systems using microcomputers. By using a sensor for various functions, such as the one for ignition, which can also be used for fuel injection, components are saved and the reliability of the system is increased. Air mass measurement is performed here using a pressure sensor and is calculated per piston stroke. However, the greatest advantage of this system is its scalability. The fuel supply can be changed at any time, allowing it to adapt to various operating conditions. Furthermore, systems such as air conditioning and ABS are also integrated with the Motronic. It calculates the optimal fuel consumption for each operating condition, and even the ignition timing can be controlled by the computer.


'However, the last paragraph is no longer accurate. The Motronic system has been using hot-wire mass airflow sensors since 1995, not hot-film sensors, and certainly does not use throttle valve measurements.'

Furthermore, an Otto engine cannot be controlled using the L-regulation because this regulation is out of operation under full load. Thinking about it more closely, it's actually impossible to control the engine using this regulation... well, it doesn't really matter now. And misses the point...

Please provide the German text you would like me to translate.
http://www.koopiworld.de/pub/motorind.htm

Just a note on the topic... the LMM (Laminar Mass Flow Meter) must detect the better filling, even in cases of resonance or other phenomena. I was mistaken in my previous understanding. What's unclear (and what others are also unsure about) is how it reacts to different flow rates. The differences should be minimal.

Hi Doctor,

Right and wrong:

1. The Lupo actually has a monochrome display - sorry for the typo in my previous message.
2. The Golf has a MonoJetronic fuel injection system.

The most important difference between Motronic and Jetronic is: Motronic controls the ENTIRE engine, while Jetronic only controls the fuel injection system. The Golf does not have a map-based ignition system, but the Lupo does. It needs it because it has cylinder-selective knock control. Both systems have almost identical mechanical designs.

I took an electronics course at MonoJet a few years ago, and I don't recall anything about a mass flow meter.
It's also correct that you mentioned the throttle angle. Both MonoJet and MonoMotronic systems have a throttle potentiometer (which often fails), but this only "estimates" the amount of air and adds fuel accordingly based on a pre-defined map. The lambda control then performs the "fine-tuning" of the fuel mixture. These injection systems do not have a true LMM (Low-Pressure Mixing Module).

Take a look at the Bosch vehicle data record; it doesn't mention a mass airflow sensor (MAF sensor) being installed! "Not for either vehicle!!"
VW (VOLKSWAGEN) Golf III Variant 1.8 07.93-09.94; Estate/Wagon; Engine: ABS
VW (VOLKSWAGEN) Lupo 1.0 10.98- ; Sedan; Engine: ALL.
It's also amusing how the control units are named: control unit, Jetronic/Motronic (MP 9.0). - So, is it Motronic or Jetronic??

Okay.

I probably should have looked into the ABS system more closely... I'm not sure anymore whether it's a MonoJet or not... but I believe you.

The difference is correct...

Both systems don't have a true LMM (Mass Air Flow sensor) in the strictest sense, as I mentioned before. Instead, they measure the airflow using valves (the DK potentiometer only provides the load state) and calculate the air mass based on the temperature. This is necessary for all systems due to the quantitative control. All of them determine the amount of air being drawn in. Each system has its own advantages and disadvantages, but going into detail would be too extensive. This also explains why the airflow sensor in the first TDI (Audi) became a mass airflow sensor in the model that came out a year later. Furthermore, both systems provide backup signals for each other, allowing the lambda control to function even if one system fails. If the L sensor is defective, the engine runs very poorly...
I just want to point out that even a MonoJet knows the amount of air it's dealing with and works with that information. Whether it's LMM (air mass meter), air mass through the bypass valve, or temperature, the primary factor is the same.

By the way, MP stands for 'druckabhängig gesteuerte Motronic,' which translates to 'pressure-controlled Motronic.' I can't really make sense of the versions without any context.

...I haven't seen any. When the throttle valve is fully open, you can directly see the electric intake air pre-heater in the intake manifold (near the ABS unit). I need to take another, closer look at the Lupo, but I didn't see anything when I changed the air filter.


...
For vehicles with smaller engines, a centralized fuel injection system (Monojetronic, Single-Point-Injection) was developed, which only had one fuel injector for all cylinders (advantage: more compact and cheaper design; disadvantage: fuel injection cannot be measured as precisely). The main control parameter, besides the engine speed, is either the throttle angle or the intake manifold pressure. They also refer to this as the load signal.
...

Source: http://www.kfztech.de/kfztechnik/motor/otto/benzinallgemein.htm

-

Yes, both are load-dependent quantities, although the DK value can be measured more precisely.

Hi Bertil,

Quote:

The fact that the used air filter had the highest "air mass flow rate" in Rainer's test series (but also certainly the highest flow resistance) leads me to believe that the MAF sensor is "lying" because the pressure conditions (within the MAF sensor) do not correspond to the stock condition (new air filter).

Why shouldn't Rainer's old filter, when in new condition, not allow for slightly more flow and therefore be better than other new parts even after 12,000 km?
Or is it a "natural" law that only K+N and similar companies can produce optimally streamlined filters?

Quote:

The wire in the mass airflow sensor (MAF) is cooled too much due to the higher airflow velocity, causing the reported air mass to be too high, leading to excessive diesel injection - resulting in black smoke. At K&N, it's quite the opposite.

This argument overlooks the aspect of air density: the faster-flowing, "thinner" air pushes fewer molecules per unit volume past the hot film, which can absorb thermal energy.

Since density is inversely proportional to volume (when mass remains constant), the whole process boils down to a rule like "double speed equals half the density," so that the same number of air molecules pass by the hot film per unit of time.
As if the LMM (mass flow meter) were located before the air filter (because the mass flow rate per unit of time is the same before and after the filter), and it were measuring the reduced flow rate (due to the "braking effect" of the poor filter) under normal pressure and flow rate.

Therefore, I cannot currently follow your argument that there is a measurement error in the LMM due to a "bad" LoF at this theoretical level.
And so, I remain with the assumption that the LMM (mass flow meter) generally captures the mass flow rate correctly, and Rainer's measurements are therefore correct in that regard.

But this also supports Rainer's claim that K&N filters don't provide any performance gain, because the amount of diesel being injected is being reduced!!!

IMO, the above consideration is now moot.

Quote:

Hi Ulf,

I assume that the air density behind the used air filter (despite the higher flow resistance) is the same as the air density behind the new filter.
Therefore, my assumption is that the LMM is "measuring" incorrectly.
I don't doubt Rainer's measurements, it's just surprising that the used air filter produced the highest reading and the K&N produced the lowest. That's why I suspected that the air filter, whether used or a K&N filter, was causing inaccurate readings.
The K&N filter doesn't necessarily have to be better than a paper filter (and I agree with you on that). It should definitely be true that a used paper filter is worse than a new one.

Hi Bertil,

Quote:

I assume that the air density behind the used air filter (despite the higher flow resistance) is the same as the air density behind the new filter.

Hmm... the higher the flow resistance, the more pressure "is lost across the filter" (again, the analogy to electrical resistance) - and I don't think that's something that can be easily dismissed.
A pressure drop at the oil filter means that there is less pressure behind it than in front of it.
And if air is suddenly exposed to a lower pressure (i.e., after passing through the filter), it expands, and its density decreases.

Therefore: the higher the flow resistance of an air filter, the lower the air density behind it (of course, under the same conditions, such as engine speed, etc.).

Or where am I going wrong?

Hi Ulf,


That's all okay and understandable. But which theory is correct (equal pressure or not)?
If the pressure drops at the filter, the air behind the air filter should also be colder. Or?