Vac operated Valve inside Airbox?

[S3DBW]

Inside the S4 airbox there is a Vac operated valve on the intake which takes it feed from just above the lower right hand radiator.

The default position for the valve is open, but does anybody know under what circumstances this valve is closed and what/where does it take its signal from?

 

[richy]

does it not close when the air that is inducted too hot and so taken from a different source?

unsure to be honest... but a wild guess never hurt...

 

[S3DBW]

Interesting thought, but given that this air inlet is seeing air which is ducted directly from the outside its always going to be the coldest available.

The other inlet is the visible one on top of the box, which again ducts air from the front of the car, so this too should only see air at whatever the ambient temperature is.

Just curious before I disconnect the vac line to leave it permanently open and see what effects, if any it has.

 

[richy]

the old saying goes..

if its not broke... don't fix it.

 

[S3DBW]

Very True, but dull!!

Just looking to see the advantages, if any, of getting some positive pressure into the airbox. By blanking of the resonator tube which exits at the back of the airbox and ensuring both other forward facing inlets are open, it should be possible to achieve some positive pressures which is always good for throttle response.

I'll let you know the outcome

 

[richy]

does the vent not go down the bulk head to the rear diff to keep it cool?

 

[S3DBW]

Quote
"does the vent not go down the bulk head to the rear diff to keep it cool"

Not sure what vent you are thinking about here?, if you mean the one that enters through the back of the air box, this terminates about 9" from the A-Pillar inside the top of the front wing, this is the intake resonator.

I still have to trace the vac line to see where its coming from, but initial trials with blocking up the resonator intake at the back are encouraging. Even my wife commented, without me telling her, that the response seemed better and what had I done to the car!