Any such thing as an airtight WG ?

[S2central.net]

We've talked around this subject before, and I know that when I tested my WG, and a lower mileage spare from an RS2 that I bought ages ago I saw the same behaviour.

Hooked up a compressed air line to the WG centre chamber (where the WGFV normally connects) and discovered this chamber is not air tight.

Its not because a leak into the upper chamber via the diaphragm, but because the air must leak along the valve guide, and presumably past the control valve seat and into the lower chamber.

Now if I can push compressed air through that route, then a small amount of exhaust gas could also push past in the opposite direction during high boost running, and potentially get into the turbo intake whilst the WGFV is directing air to the MAF hose.

Tested my car yesterday with the WGFV disonnected and saw only 0.4bar boost with the WG spring alone. My WG is totally stock and has never been messed with.

So, I have a couple of questions - that I can't answer as my spare WG is in storage.

1. Can this behaviour be improved by stiffening the spring - effectively clamping the valve tighter into its seat and reducing WG 'creep' ?

2. Can the WG valve and the seat in the lower chamber be ground like a normal engine valve for an improved gas seal ?

The reason for Q2 is the WG valve must build up a certain amount of carbon deposits over time and that is bound to prevent it from making an airtight seal.

The reason I ask is that my car now has an annoying whistle on max boost - could be a shot turbo after 125k miles (some quite harshly driven) - or a cracked EM, but I also want to rule out the possibility of a worn WG.

I know some lads on the forum have access to machine shops so it should be easy to get the WG reconditioned/upgraded to a (more) airtight state of play. I'd happily offer up my spare one to scientific research, but its in storage...


Paul

[martinjs]

Paul, when i had a running problem last year i did think it might be the WG causing it. (erratic boost behaviour) especially after seeing steveh's old valve out of his WG which was very worn, mine had done 210k miles so decided to fit the spare WG i had, which had no play on the main shaft and was in generally good condition.
It didnt cure my problem btw.
So i took my original WG to bits, The main shaft had a bit of wear to it but it wasn't the cause of my problem.....which i never did find out what it was, it was cured when i had the car mapped properly by mihnea.

I'll dig the WG out (its all in bits somewhere) and post some pics later.
Agreed there is the possibility of gasses escaping up through the valve, but once the WG has opened slightly under boost i cant see a way of it being totally air tight.

martin

[S2central.net]

Agreed there is the possibility of gasses escaping up through the valve, but once the WG has opened slightly under boost i cant see a way of it being totally air tight.

martin

Agreed on that too... just think its a bit of weird engineering that the WG valve guide has to have sufficient clearance to prevent the WG from sticking, but there is no method of preventing leakage into the control chamber.

Obviously the vast majority of exhaust gas will take the path of least resistance by jumping down the WG pipe and into the exhaust system, but the possibilty of some exhaust gas 'crossing over' is a bit concerning for me.

Extremely hard to measure this of course... then again maybe not - guess I could remove the WGFV from where it connects to the MAF hose and hook up an exhaust gas analyser. Actually there's another thought - wonder how the thing would drive with the WGFV connected to atmosphere instead of the MAF hose - guess you'd have to radically increase the WGFV duty cycle in order to reduce the pressure presented to the WG control chamber... Sorry just thinking out loud here...


Paul

[audiman]

I have my WGFV venting to atmosphere. Makes no difference. There is no reason that the valve and seat couldnt be recut/ground in. Sounds like a very good idea. Also, where the dia. goes on the shaft, isnt that supposed to be sealed with loctite or something to stop pressure escaping there too???

[S2central.net]

Glad to hear someone else has a WGFV venting to atmosphere, but I'd like to know from a recent resident of Belgium if he had to modify WGFV duty cycle as a result.

The upside of doing this is that if there is any exhaust gas escaping the control port, then your dump yours to atmosphere instead of the turbo intake (via the MAF hose).

Do us a favour - stick an exhaust gas analyser onto your WGFV hose that vents to atmosphere and see what you can sniff under boost...


Paul

[audiman]

Only problem is the EGA isnt really suitable for testing whilst driving, and i havent got a RR I will see what i can do tho for you