Okay, so i'm confused from STFA...at idle is the wastegate open or closed? Open right?
10-27-2004, 11:23 AM
#5
....it's opened via boost.
With the N75, the ECU chooses when to allow boost to go to the wastegate to open it up.
So even if the ECU opened teh N75 all the way, you still won't open the wastegate, since there's no boost.
So even if the ECU opened teh N75 all the way, you still won't open the wastegate, since there's no boost.
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10-27-2004, 11:35 AM
#8
you generate boost by having the wastegate closed.., BUT
He was asking how it opens. The wastegate actuator is opened by applying boost to it.. applying boost OPENS the wastegate. The N75 is controlling boost (choosing how much and when boost is allowed to go to the actuator)
Wastegate is closed under idle since there's no boost to open it... and not enough flow to generate boost.. so in that situation, it's closed without boost.
Wastegate is closed under idle since there's no boost to open it... and not enough flow to generate boost.. so in that situation, it's closed without boost.
10-27-2004, 11:58 AM
#10
AudiWorld Expert
Here's some helpful hints...
In general,
- When the wastegate is open, that means air is bypassing the turbine (exhaust) side of the turbo.
- When the wastegate is closed, that means air is flowing through the turbine side of the turbo.
(even if stuck fully open, some air would be flowing through the turbine)
- The car's N75 (Boost Frequency Valve) allows an amount of air to flow to the wastegate (inverse to it's reading). A certain amount of pressure on the wastegate will open it a certain amount. Depending on how far closed/open it is, controls how much work the turbo is doing to pressurize the intake side.
- The higher the % you log for the Boost Frequency Valve (N75), the lower the amount of air gets to the wastegate, the higher percentage the wastegate is closed, and thus more boost is created.
If we look at some cases:
<b>Fully Closed: </b>
- This is how the car is at idle. This way, when you first want boost to build up, the wastegate is already closed, forcing all air through the turbine to spin up the turbo.
<b>Closed at idle (and Fully Open):</b>
- The other way you will notice this fact (closed by default) is when a car goes into "Limp Mode". You see, in limp mode, the car is telling the turbo to not do any work at all. That is, it's telling it to open the wastegate all the time. That is, the N75 allows all air to flow to the wastegate. The wastegate itself has a spring on it which exerts a physical pressure to keep it closed. Therefore, as air begins to flow to the turbine, it is still fully going through the turbine because not enough pressure is present to open the wastegate spring. Once there is enough pressure, that's when it opens up. You'll notice that the pressure needed is about 5 PSI, and thus why our cars see 5 PSI when in limp mode. There is no way to program the car with software to go any lower than this pressure, as it's a mechanical constraint due to the spring.
<b>Opens with Boost:</b>
- Well, I guess the 2nd example above really describes fully open. However, to illustrate that the waste gate opens with boost, all you have to do is check out a car with an External Wastegate. See our turbos have them built in, and thus when the air is diverted, it still goes out our stock exhaust path. A lot of cars with an External Wastegate don't provide a path for the exhaust to flow (and certainly don't use mufflers on it). Thus, when one of these cars reaches the desired boost level, the wastegate opens and the car gets very loud.
Hope that helped with some overview on this topic.
- When the wastegate is open, that means air is bypassing the turbine (exhaust) side of the turbo.
- When the wastegate is closed, that means air is flowing through the turbine side of the turbo.
(even if stuck fully open, some air would be flowing through the turbine)
- The car's N75 (Boost Frequency Valve) allows an amount of air to flow to the wastegate (inverse to it's reading). A certain amount of pressure on the wastegate will open it a certain amount. Depending on how far closed/open it is, controls how much work the turbo is doing to pressurize the intake side.
- The higher the % you log for the Boost Frequency Valve (N75), the lower the amount of air gets to the wastegate, the higher percentage the wastegate is closed, and thus more boost is created.
If we look at some cases:
<b>Fully Closed: </b>
- This is how the car is at idle. This way, when you first want boost to build up, the wastegate is already closed, forcing all air through the turbine to spin up the turbo.
<b>Closed at idle (and Fully Open):</b>
- The other way you will notice this fact (closed by default) is when a car goes into "Limp Mode". You see, in limp mode, the car is telling the turbo to not do any work at all. That is, it's telling it to open the wastegate all the time. That is, the N75 allows all air to flow to the wastegate. The wastegate itself has a spring on it which exerts a physical pressure to keep it closed. Therefore, as air begins to flow to the turbine, it is still fully going through the turbine because not enough pressure is present to open the wastegate spring. Once there is enough pressure, that's when it opens up. You'll notice that the pressure needed is about 5 PSI, and thus why our cars see 5 PSI when in limp mode. There is no way to program the car with software to go any lower than this pressure, as it's a mechanical constraint due to the spring.
<b>Opens with Boost:</b>
- Well, I guess the 2nd example above really describes fully open. However, to illustrate that the waste gate opens with boost, all you have to do is check out a car with an External Wastegate. See our turbos have them built in, and thus when the air is diverted, it still goes out our stock exhaust path. A lot of cars with an External Wastegate don't provide a path for the exhaust to flow (and certainly don't use mufflers on it). Thus, when one of these cars reaches the desired boost level, the wastegate opens and the car gets very loud.
Hope that helped with some overview on this topic.