[vasillalov]

I've been gathering some logs of my car and I am seeing a discrepancy between the WGDC between each turbo. So, I've been wondering:

1. Is it normal for a small discrepancy to exist between the waste gate duty cycles on the two turbos?

2. What is considered an example of a good WGDC at WOT? Can we see some graphs as examples please?

Thanks in advance.

[vasillalov]

bump. anyone care to take a stab at this?

[nitehawk]

n00b question, does a WGDC of 0 mean fully open (as in valet mode)?
I'd like to start logging data on this.

[Joshboody]

Each WG is getting the same vacuum, both solenoids feed the same line.

[JamesM3M5]

Originally Posted by Joshboody

Each WG is getting the same vacuum, both solenoids feed the same line.

Yeah, they're connected together. So I don't see how one solenoid would have a different DC than another, unless the ECU can detect minor variations in reaction time of the solenoids and adapt accordingly.

[GoodtoGo]

Originally Posted by Joshboody

Each WG is getting the same vacuum, both solenoids feed the same line.

I have noticed this and I honestly don't know why the n54 even uses two WG solenoids and controls them individually if the vacuum lines are joined.

[vasillalov]

There are indeed 2 vacuum converters, one for each turbocharger. Those are items number 4 on this diagram:



How would one interpret a WGDC log at all? I mean, it is nice to be able to log all this data, but what does it mean and how does one determine if a problem exist?

[JamesM3M5]

That is true, but there is a piece of vacuum hose T connected between the two solenoids. They are incapable of controlling the turbos independently with that little piece of hose there. I suspect it's for redundancy, not for individual control.

Additionally, the ECU would need individual compressor output pressure transducers to determine whether one turbo needed a WG adjustment versus the other. Our cars have two MAP sensors, but they are both post intercooler where the charge pressure is homogeneous as far as the two turbos are concerned.

[vasillalov]

Thank you for the clarification. That answers question 1. What should we be seeing as a WGDC values when logging a car with "healthy" turbochargers?

[JamesM3M5]

Hell, I'd think 80-90% at peak boost? Maybe 100% for very brief periods? It would definitely depend on levels of modification. Stock everything means higher WGDC to achieve/hold the same boost as a car with intake and exhaust mods. Problem is achieving and holding 1, 2, 5, 10, 15 psi and checking via logging. It would require several users to undergo the same test procedures and report findings, and even then, improper technique and other factors would muddle the results.

[Ilma]

Generally.......a wastegate duty cycle hovering around 50% seems to the norm.

Even at peak boost. I'm running 17-18 psi of boost here with a stock exhaust.
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[BMWsky]

I'd really like to know this too. When I've done my logs, I seem to recall both WG's really close to each other and at WOT they seem to have touched 30 or so before leveling out closer to mid 40's to 50.

[Clarkson]

This seems legit to me:

http://www.cobbforums.com/forums/sho...w-to-interpret

I think of it this way.
Maximum Boost achievable = Fixed WG spring pressure + WGDC allowed pressure

From my experiments with the WGDC table.
40 in the ATR table equates to approx 100% observed/logged WGDC.

Once you hit 100% WGDC, that is all she has got.

[vasillalov]

Thank you for this link!

[JamesM3M5]

Originally Posted by Clarkson

This seems legit to me:

http://www.cobbforums.com/forums/sho...w-to-interpret

I think of it this way.
Maximum Boost achievable = Fixed WG spring pressure + WGDC allowed pressure

From my experiments with the WGDC table.
40 in the ATR table equates to approx 100% observed/logged WGDC.

Once you hit 100% WGDC, that is all she has got.

Hold on there. That's for a Mazda Speed 3, not a BMW. The BMW boost control is backwards to typical boost control systems. The boost pressure does not directly control the wastegate actuators. The wastegates rest fully open, i.e. no boost. The vacuum pump sucks down those two canisters. The ECU switches the solenoids to open, allowing the vacuum to reach the WGAs. The vacuum starts to suck the wastegates shut. Then the ECU regulates the solenoids via duty cycle to maintain proper boost pressure developed, which is read after the intercooler but before the throttle. (The sensor in the manifold is used as a redundancy check.)

Therefore, WGDC means wastegate is more closed, which results in higher boost pressure. The numbers are the same - higher WGDC means more boost, but the rest of the logic in the other forum post does not apply to these cars.

[rader1]

Originally Posted by JamesM3M5

Hold on there. That's for a Mazda Speed 3, not a BMW. The BMW boost control is backwards to typical boost control systems. The boost pressure does not directly control the wastegate actuators. The wastegates rest fully open, i.e. no boost. The vacuum pump sucks down those two canisters. The ECU switches the solenoids to open, allowing the vacuum to reach the WGAs. The vacuum starts to suck the wastegates shut. Then the ECU regulates the solenoids via duty cycle to maintain proper boost pressure developed, which is read after the intercooler but before the throttle. (The sensor in the manifold is used as a redundancy check.)

Therefore, WGDC means wastegate is more closed, which results in higher boost pressure. The numbers are the same - higher WGDC means more boost, but the rest of the logic in the other forum post does not apply to these cars.

Thanks for the info/heads up

[nitehawk]

Viewing live data on my Cobb AP, the WGDC hovers around mid 30s at WOT in 3rd gear.