Updated Boost Control/WGFV Diagram

[UrS4boy]

Paul: Hope you don't mind. I did this this AM on my home forum to answer a question about the orientation of the N75 WGFV legs. Based on your diagram from S2Central.net but I've added some photos and comments.

Not sure if the upload will kill the resolution or not (I hope not).

Wastegate frequency valve info (click on the label in the lower left corner of the diagram (the other labels are live as well):

http://members.shaw.ca/speedtek/UrS%20Engine%20Bay%20Device%20Map.html

[UrS4boy]

Updated the diagram with fuel condenser (moisture trap) info.

[Thuppu]

The wastegate doesn't work like that.

[Jamo]

Agree wastegate is wrong way around as gas come in under the valve not through the side as shown in diagram

[cooperquattro]

The wastegate doesn't work like that.

it does on stock aby!! top part of w/g bleeds to air as standard

[Jamo]

Show me a stock ABY where the exhaust from the manifold comes into the waste exit rather than the entry?

[cooperquattro]

Show me a stock ABY where the exhaust from the manifold comes into the waste exit rather than the entry?

ahh ,i was refering to the n75 pipe work,ye agrree exhaust gas is wrong

[UrS4boy]

The wastegate doesn't work like that.

Agree. The diagram (not mine originally, VAG and then Paul N) is a schematic, trying to illustrate the basic principles of how the overall system works, not an exact replica of every component. I agree the exhaust enters the bottom of the wastegate and exits through the side but it is still exiting (or not) because of the wastegate valve and the actions (or not) of the wastegate spring and/or boost pressure as controlled by the ECU via the N75 WGFV. That is the point.

Quiz: What happens when you disconnect the pressure line between the WGFV and the wastegate?

A partially disassembled WG, photo courtesy of SJM Autotechnik:

[Avantus]

Quiz: What happens when you disconnect the pressure line between the WGFV and the wastegate?

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boost is unlimited then.

or atleast untill you get a boostcut.

[UrS4boy]

boost is unlimited then. or at least untill you get a boostcut.

Correct - Or until something blows up.

Bottomline: the WG is never going to open if that pressure hose between the WGFV and the lower chamber of the WG is disconnected.

[4WheelDrifter]

Quiz: What happens when you disconnect the pressure line between the WGFV and the wastegate?

Or:

What happens when you use a silicone hose that gets brittle due to heat?

[cooperquattro]

not strictly true!!!if there is no hose on the w/g then the opening point will be spring pressure,meaning the exxhaust gas will open the valve at the given pressure,NOT give unlimited boost

[Jamo]

Having done this as a test I can tell you you get boost until ecu cut
That was with a 1.1 bar spring and k26/k27
Cooperquattro it will only open at spring pressure with a boost source to the lower chamber

[prj]

boost is unlimited then.

or atleast untill you get a boostcut.

You can't get a boost cut, the ECU has no control over boost.
You can get a fuel cut, if that is not disabled in ECU.

not strictly true!!!if there is no hose on the w/g then the opening point will be spring pressure,meaning the exxhaust gas will open the valve at the given pressure,NOT give unlimited boost

You will never reach that point because your engine will blow up first/you will reach the limit of the compressor, unless you are running a 0.1 bar spring or something.

So yes, basically it will boost as much as the turbo is capable of.

[driftin jo]

not strictly true!!!if there is no hose on the w/g then the opening point will be spring pressure,meaning the exxhaust gas will open the valve at the given pressure,NOT give unlimited boost

Wrong, there might be a little gas pushing past the wast gate but not enough to stop out of control spool of the turbo, as said above the only thing stopping unlimited boost is the ECU cutting the fuel pump. If you don't believe it then hard wire you fuel pump and try it, you will get 2.5 bar, just before your con rods are turned into bananas.