Source of vacuum on FSI?

A2Steve

A2OC Donor
Wales
Since increasing the turbo pressure on my FSI I’ve been having quite loud churping from back pressure when the throttle is closed. Not a bad sound at all, but certainly not doing the turbo any good.

The planned and fitted fix was a Blow off valve or “dump valve”. Fitting has gone fine and has eliminated the back pressure.

Now to my question. The dump valve relies on vacuum pressure and boost pressure to open and so I’ve take a vacuum feed from the upper inlet manifold. This vacuum pressure is too great. It’s opening the dump valve at relatively low pressures and so I need a vacuum source on the FSI that’s going to be at a lower pressure.

Can anyone with some knowledge of the FSI think of a source of vacuum after the throttle body?
 
Can you take the dump valve apart. Usually there is an internal spring that controls the pressure. By fitting a stronger spring you then increase the pressure. There were dump valves a while ago that had a screw and lock nut where you could adjust the pressure by increasing the spring pressure in the valve.
 
Alternatively you could fit an electronic dump valve kit such as this one...


 
Yes it’s an adjustable one that I’ve fitted, already on the hardest setting and loosing pressure under acceleration. With the vacuum disconnected the car is boosting fine and only blows off at the dump valve after closing the throttle at 4-5k revs.


Could you put a threaded adjuster into the existing vacuum line so that you can vary the input?

Now that’s something I hadn’t thought of. A bleed valve essentially?
 
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Alternatively you could fit an electronic dump valve kit such as this one...



Im not sure what the electronic element of that one is but apart from the diverter part it’s essentially what I have fitted as below.

4913FBE7-B6B5-4F03-8F70-66EACCA86565.png
 
Yes it’s an adjustable one that I’ve fitted, already on the hardest setting and loosing pressure under acceleration. With the vacuum disconnected the car is boosting fine and only blows off at the dump valve after closing the throttle at 4-5k revs.




Now that’s something I hadn’t thought of. A bleed valve essentially?
I don't think an adjustable valve in the vac line would work. A valve will only vary pressure (neg or pos) if there is flow across the valve. You need flow to create a pressure drop. In @A2Steve application, the vac line is a closed circuit, so, no flow.
What about the vac line into the solenoid valve that controls the flap actuator? From the crankcase I think.
I'm guessing it's not used on Black Beauty?
Mac.
 
I don't think an adjustable valve in the vac line would work. A valve will only vary pressure (neg or pos) if there is flow across the valve. You need flow to create a pressure drop. In @A2Steve application, the vac line is a closed circuit, so, no flow.
What about the vac line into the solenoid valve that controls the flap actuator? From the crankcase I think.
I'm guessing it's not used on Black Beauty?
Mac.

Yes I was thinking of using that one as the vacuum pressure may be sightless lower than connecting to the upper inlet directly. I think I’ll have a play about with it later and see if I can find a suitable source.

Im only guessing here, but I wonder whether the high compression ratio of the FSI engine is the reason behind the high levels of vacuum. Obviously on a car that’s been designed to be a turbo’d car from factory then the compression ratio would be a lot lower and have a lower vacuum pressure?
 
Fit a vacuum regulator? You can then set the vacuum to that required.

RAB
 
Now that’s something I hadn’t thought of. A bleed valve essentially?
[/QUOTE]

I'm guessing so - it was an off the cuff idea and I think has already been countered by someone knowing what they are talking about in the next couple of posts above - but then wonder if @RAB 's vacuum regulator is essentially what I was intending using the correct terminology.
 
Yes I was thinking of using that one as the vacuum pressure may be sightless lower than connecting to the upper inlet directly. I think I’ll have a play about with it later and see if I can find a suitable source.

Im only guessing here, but I wonder whether the high compression ratio of the FSI engine is the reason behind the high levels of vacuum. Obviously on a car that’s been designed to be a turbo’d car from factory then the compression ratio would be a lot lower and have a lower vacuum pressure?
Vacum is usually created, at least in cars, with a venturi, like a carburettor (remember them?). Air flows through a narrowing path, to raise pressure, then the path widens, the air pressure drops, and creates a vacum. You tap off of that to power your actuator etc. As long as the circuit is closed, it works. If you fit something to regulate the vacum to your device, you should also fit a non return valve between the source of the vacum and the regulator, so you only regulate the vacum to your device, not the vacum circuit itself (don't want to upset the brake servo for example!).
Mac. .
 
I’m not familiar with those, could you show me an example?

Choosing the correct one with the correct specification might be a problem. I'll leave that to you!

A vacuum regulator is also a non-return valve, i.e. it only regulates downstream. Note that there would have to be flow downstream of the regulator, otherwise the vacuum would be fixed which is perhaps not what is required.

RAB
 
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Thanks for that Rab.

Another adjustable valve to incorporate into the system ?

Between the boost controller the adjustment on the blow off valve and possible adjustment of vacuum it’s going to take me weeks of trial and error to find the perfect setup.
 
I’ve just been out and disconnected the vacuum pipe that runs from the outlet at the top of the manifold to the solenoid for the flaps. Can’t see it causing an issue because it’s redundant on a Pro Boost car.

I haven’t been able to take it for a drive yet, but just revving it in the garage I can hear no loss of boost under load and even got a little bit of back pressure through the turbo implying that there is now a little bit of room to soften the dump valve slightly.

Will take it for a run later but fingers crossed it’s working.
 
Caution! The vacuum regulator requires that the vacuum source is on the downstream/outlet side of the regulator, which is less than ideal!

RAB
 
Hmmm

Just took it for a run and no it’s still loosing pressure under acceleration, remove the vacuum and the cars fine again.

Perhaps the only real option is a higher rated spring?
 
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Hmmm

Just took it for a run and no it’s still loosing pressure under acceleration, remove the vacuum and the cars fine again.

Perhaps the only real option is a higher rated spring?
@A2Steve e
Have a read here:
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I'll have a ponder too.
Mac.
 
The TFSI turbo has an inlet for recirculated pressure already in place. At present the crankcase is breathing back into it.
 
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