Altitude Acclimation & Emergency Procedures

hi,
Here's a story from my vacation in the Alps.
During trips between altitudes of 1000-2000 meters, the boost pressure was up to 0.15 bar (0.7 bar absolute) higher than at sea level.
The Überschinger were also shifted upwards to this size.
In my opinion, it is explainable and can achieve the same performance.
After a long period of inactivity at an altitude of 2000 meters, my T4 was restarted, but it had no power.
Emotionally, the message seemed to be in a state of emergency.
After driving for just a few meters, everything was back to normal.

On the way back to Berlin, the tire pressure remained within the usual range (0.55 bar).

Okay, here are my questions:
Is the altitude adjustment normal when the boost pressure is increased?
Are there any altitude limits that could cause the motor to go into emergency mode?

Hi Leo,

Hello,

How do you measure your boost pressure?
As a pressure sensor in an analog or digital display instrument?
The error lies in the measurement method.

'Conventional' boost gauges display the overpressure that is generated. However, this value changes depending on the ambient pressure, as the boost pressure is regulated from a manifold absolute pressure (MAP) to an absolute pressure.

Okay, gib mir den deutschen Text, den du übersetzt haben möchtest.
You have 0.55 bar of positive pressure at sea level: In this case, your MSG (Manifold Supply Gauge) reads 980 mbar ambient pressure and regulates to 1535 mbar LD (Line Differential). Your LD (Line Differential) display sees the difference and shows 0.55 bar LD.

At higher altitudes, the ambient pressure is decreasing.
Your MSG (Manifold Static Gauge) shows 965 mbar, which is 0.15 bar less. However, to achieve the same performance, I still need to regulate the LD (Laser Diode) to 1535 mbar.

What does the differential pressure gauge show now?
Correct: 1535 mbar - 965 mbar = 570 mbar (0.57 bar ).

Since the engine power can change at high altitudes or in bad weather conditions, the MSG system regulates based on absolute pressure.

However, there is still an altitude adjustment feature.
As you can see from the example above, the turbocharger has to overcome a greater pressure difference at higher altitudes than at sea level. This simultaneously means higher compressor speeds, which would eventually overload the turbocharger.
Therefore, as the altitude increases, the turbocharger pressure is reduced, and the engine power is decreased.

Best regards, Jochen.

Jochen_145 wrote:

Hello, How do you measure your boost pressure? As a pressure sensor in an analog or digital display instrument? The error lies in the measurement method. "Conventional" boost gauges display the overpressure that is generated. However, this value changes depending on the ambient pressure, as the boost pressure is regulated from a manifold absolute pressure (MAP) to an absolute pressure. Okay, gib mir den deutschen Text, den du übersetzt haben möchtest. You have 0.55 bar of positive pressure at sea level: In this case, your MSG (Manifold Supply Gauge) reads 980 mbar ambient pressure and regulates to 1535 mbar LD (Line Differential). Your LD (Line Differential) display sees the difference and shows 0.55 bar LD. At higher altitudes, the ambient pressure is decreasing. Your MSG (Manifold Static Gauge) shows 965 mbar, which is 0.15 bar less. However, to achieve the same performance, I still need to regulate the LD (Laser Diode) to 1535 mbar. What does the differential pressure gauge show now? Correct: 1535 mbar - 965 mbar = 570 mbar (0.57 bar ). Since the engine power can change at high altitudes or in bad weather conditions, the MSG system regulates based on absolute pressure. However, there is still an altitude adjustment feature. As you can see from the example above, the turbocharger has to overcome a greater pressure difference at higher altitudes than at sea level. This simultaneously means higher compressor speeds, which would eventually overload the turbocharger. Therefore, as the altitude increases, the turbocharger pressure is reduced, and the engine power is decreased. Greetings, Jochen

.
hi jochen,
Yes, my LDA is analog!
I don't understand three things!
The difference between 980 and 965 millibars is 0.015 bar, isn't it?
2. Shouldn't analog LDAs only measure/estimate pressure based on spring force?
Surely, the ambient pressure should only contribute a very small proportion to the measurement result?
3. At an altitude of 2000 meters, the pressure is likely 830 mbar (normalized to 1030 mbar at 0 meters)?

Hi Leo,

hi jochen,
Yes, my LDA is analog!
There are three things I don't understand!
The difference between 980 and 965 millibars is 0.015 bar, isn't it?
2. Shouldn't analog LDAs only measure/estimate pressure based on spring force?
Surely, the ambient pressure should only contribute a very small proportion to the measurement result?
3. At an altitude of 2000 meters, the pressure is likely 830 mbar (normalized to 1030 mbar at 0 meters)?

hello leo


Good night,
Okay, it's later, and I made a mistake in my calculation. The correct value should have been 830 millibars.
Then the calculation will be correct again.

The examples provided are merely illustrations and should, on their own, demonstrate why the display is showing an incorrect reading.

If you have a gauge that displays vacuum pressure (e.g., -1 bar), you will only be able to achieve this with a differential pressure measurement.
My old VDO instrument works exactly like that. The needle points differently depending on the weather conditions.
I haven't driven my convertible in the Alps yet.

... remains at 0 bar even under pressureless conditions, even at an altitude of 2000 meters.
Measurement range: -1.0 to +2.0 bar. Manufacturer: "jom".

Hi Leo,

... is always at 0 bar when not in use, even at an altitude of 2000 meters.

Of course.
what does 'drucklos' mean?
Engine off, or turbo not in operation, therefore LD = ambient pressure.

Therefore, the differential pressure is 0 bar!

The turbocharger needs to be working for you to see this phenomenon.
Oh, sorry, you already .

Best regards, Jochen.

I can only say one thing about that:
Analog or digital displays show the pressure difference relative to the ambient pressure. If you drive into the mountains, the zero point of your display should change (if it's a "good" display). If it doesn't adjust, then the readings are inaccurate.

I'm comparing this to my tire pressure gauge, which has an adjustable scale. Most of the time, I don't need to calibrate it, but in extremely bad or good weather, I sometimes have to adjust the zero point. The boost pressure gauges don't have that same function.

Your engine control unit regulates the boost pressure in relation to the ambient pressure. The effective boost pressure does not increase! The turbocharger simply has to work harder to build up the pressure. That's why turbocharged engines have less or no power loss compared to naturally aspirated engines when driving in the mountains. I'm thinking of my last motorcycle trip in the Alps.

Quote:

.. is always at 0 bar when not in use, even at an altitude of 2000 meters.

The mechanical LDA cannot display values less than 0 bar, or is there no stop/pin for the pointer?

Rainer K. wrote:

Quote: .. is always at 0 bar when not in use, even at an altitude of 2000 meters. The mechanical LDA cannot display values less than 0 bar, or is there no stop/pin for the pointer?

Look what he's writing:

Quote:

.. measurement range: -1.0 to +2.0 bar manufacturer: "jom"

So, theoretically, it is already possible.

I guess that this device measures the overpressure or underpressure compared to the sea level pressure (1000 mbar). The only question that remains is why this device shows a higher reading in the mountains than at home. According to this theory, it should show a lower reading .

Hmm, or is my theory about the control unit wrong?
What do you think about that, Rainer?

Hi,

I would say whether it indicates more or less depends on how it is mechanically constructed.
The best way is to check measurement block 10 in the engine control unit (ECU) using a diagnostic tool, as it contains information on ambient air pressure and boost pressure. These are measured by two separate sensors.

Best regards, Rainer.

Hello everyone,

Typically, these simple and inexpensive LD displays are differential pressure instruments that compare the LD reading with the (current!) ambient pressure.
I have already explained the operating principle above. The ambient pressure is then the air pressure in which the instrument is located.
These instruments can be identified by the fact that they only use the pressure hose as a connection, linking to the intercooler system.
(+ possibly two cables for the lighting)


Best regards, Jochen.

Jochen_145 wrote:

Hello you two, Typically, these simple and inexpensive LD displays are differential pressure instruments that compare the LD reading with the (current!) ambient pressure. I have already explained the operating principle above. The ambient pressure is then the air pressure in which the instrument is located. These instruments can be identified by the fact that they only use the pressure hose as a connection, linking to the intercooler system. (+ possibly two cables for the lighting) Greetings, Jochen

.

"That's understandable, but why does this device also show a higher pressure reading at higher altitudes? Since the external pressure is lower, the displayed pressure should also be lower, but according to leo_b, it's actually higher."

The 'classic' boost pressure gauges indicate the overpressure that is generated. However, this changes depending on the ambient pressure, because the boost pressure, measured by the MAP sensor, is regulated to an absolute pressure .

Okay, gib mir den deutschen Text, den du übersetzt haben möchtest.
You have 0.55 bar of positive pressure at sea level: In this case, your MSG (Manifold Supply Gauge) reads 985 mbar ambient pressure and regulates to 1535 mbar LD (Line Differential). Your LD (Line Differential) display sees the difference and shows 0.55 bar LD.

At higher altitudes, the ambient pressure is decreasing.
Your MSG (Manifold Static Gauge) shows 835 mbar, which is 0.15 bar less. However, to achieve the same performance, I still need 1535 mbar of LD (Line Pressure) that is being regulated.

What does the differential pressure gauge show now?
Correct: 1535 mbar - 835 mbar = 700 mbar (0.7 bar ).


ok, it's later, I made a mistake in the calculation; 830 mbar would have been the correct value..

'Those who can read have a clear advantage.'
I have 'as a precaution' corrected the calculation error in the quote, so it should be clear now.

Best regards, Jochen.

Okay, I get it now.

Thank you, Jochen.

Okay, let me summarize this:
I assume the message is fine.
Therefore, the LD regulation works.
So, the motor is filled with a pressure of 1,550 bar (absolute).
At an absolute ambient pressure of 0.850 bar, this represents a difference of 0.700 bar (as described above).
2. Since the LDA (Laser Doppler Anemometer) always remains at its zero setting, it can only be a differential measurement instrument.
The internal pressure (measured value) corresponds to the external pressure in the idle state.
Therefore, the LDA (Laser Doppler Anemometer) must display a reading of 0.700 bar at an altitude of 2000 meters.

"quod erat demonstrandum"

4. Consequently, the LDA can serve as a load indicator for the turbo.

Hi Leo,