Pneumatic LD Oscillators: Reduce & Optimize

Hello,

During the transition from idle to full throttle, the turbocharger (LD) quickly increases its speed, typically above ~1500 rpm, depending on the engine. To minimize overboost, the variable turbine geometry (VTG) must be opened with precise, millisecond-level timing as it approaches the target value.
"In engines that have been modified with performance chips, the increase in power output when accelerating at full throttle is generally faster than in the standard configuration, which can exacerbate over-revving. While the LD pre-throttle control can help mitigate this, it can also noticeably slow down the engine's response."
The software in my Polo is designed as a compromise, and so far, my LDA (Linear Dynamic Amplifier) has shown peaks of up to approximately 0.2 bar above the target pressure.

A weasel bite to the pressure line from the air-oil cooler (LuFiKa) to the engine pneumatics, combined with VAG's replacement parts policy, has unexpectedly resulted in a significant reduction in the LD over-travel.
The conical hose with the bite mark is not sold individually, but only as part of a complete set of hoses and tubes for pneumatics, and that was simply too expensive for me.
Therefore, I removed the external pressure components between the air filter housing (LuFiKa) and the solenoid valve block and sealed the connection stub on the air filter housing with a metal screw. The outside air now enters through a small fuel line filter, which is connected to the solenoid valve block via a short piece of hose.
Since then, the LDA has been showing pressure peaks that are about 0.1 bar lower when the engine is running at full throttle.

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

"Explanation:
"
The VTG (Variable Turbine Geometry) only opens when air flows into the charge air cooler, and this happens through very small OEM flow passages and long lengths of the external pressure line. The tapping hole in the air filter housing of the Polo (Ibiza / Fabia) is estimated to be only 1-1.5 mm in diameter!
This bottleneck restricts the airflow towards the charging chamber, thereby limiting the opening speed of the VTG (Variable Turbine Geometry) and causing significant overshoots.
The fuel line filter and the new hose piece, on the other hand, have virtually no flow resistance, which allows the VTG (Variable Turbine Geometry) to open more quickly and with smaller overshoots.

The significant reduction of a damping component (i.e., the air flow resistance on the way to the charging chamber) of the overall LDR system, while causing the charging chamber to oscillate slightly more during initial adjustment, results in a significantly reduced material stress overall.

The effect of such a modification depends, of course, on the previous flow resistance between the air filter box (LuFiKa) and the LD valve. This can be roughly tested by sucking through the magnet valve end: If you feel a noticeable "straw" effect while sucking, whereas you can suck relatively freely through the planned extra filter and hose, then I would expect a similar reduction in over-revving as I experienced with my Polo – provided that all components of the LD system are in good condition.

I'll give it a try; it would be almost too good to be true if...
that it would also have an effect on my AFN. It would actually be a good fit for...
"It fits my VTG rod, which is slightly shorter."


Best regards, Klaus.

I wish I had a swing set.

My 1.5 bar press (2500 mbar absolute pressure) is programmed with such precise zero-swing settings that it often doesn't apply enough force to the material.
Thanks to the pressure gauge on the can, you can see how "agitated" it gets long before reaching the 2500 mbar mark.

Perhaps I could use Ulf's observation in a "reverse" way...

m;

Klausel wrote:

I'm going to try that; it would be almost too good if that it would also have an effect on my AFN. It would actually be a good fit for... My VTG rod, which is slightly shorter, fits.

Based on my experience with my G3 AFN, I estimate that there will be less adjustment needed, because the pressure line between the air filter housing and the VTG valve is very short.

Quote:

Unless the drain hole in the air filter housing is a similar flow restrictor as it is in the Polo, then you can simply drill it out to match the inner diameter of the solenoid valve ports. However, you can probably save yourself 99% of the cost by not buying the bypass filter and extra hose.

My 1.5 bar press (2500 mbar absolute) is programmed so precisely to avoid any oscillation that it would rather not pull enough on the material.
Thanks to the pressure gauge on the can, you can see how "agitated" it gets long before reaching the 2500 mbar mark.

Perhaps I could use Ulf's observation in a "reverse" way... } Then you would need to incorporate something into the current path of the servo motor that throttles the current in the "VTG open" direction: for example, a resistor that is bypassed in the "VTG close" direction by a diode.
It's just a random thought, I have no idea if it could actually work.

Sorry if I'm about to ask something really stupid: In the crucial...
The adjustment point should be located at the injection point.
The outside pressure in the LuFiKa is actually good, meaning there is a good vacuum.
because it is located within the suction area of the powerful turbocharger.
Perhaps this contributes much more to this "Ulf's effect"...
Then I would also have hope regarding my AFN.

Best regards, Klaus.

Klausel wrote:

At the crucial moment of the pressure regulation, there should actually be good vacuum at the injection point of the external pressure at the air filter housing (LuFiKa), because it is located in the suction area of the powerfully operating turbocharger.

As long as the air filter is not completely blocked, the injection point will always emit (almost) external pressure, because there is no rapid flow there that could create a pump injector suction effect.