My 3B to RS2 project

[newsh]

Just fixed the interior lights which hadn't worked for 4 1/2 years. Thread Here
This was as the result of investigating a problem with the central locking which turned out to be related to broken wiring loom under the carpet near the bonnet pull.

[newsh]

Cheers Paul
Yes, thats where I'm up to with it. Could be there's some buld up of carbon on the valve stem preventing it from opening fully and I didn't notice on the other turbo cos it didn't blow hard enough at the top end.

At the moment the car drives a bit like a sports bike, its as if it comes on cam at 4.5k starts boosting and just builds power to the redline as the boost gauge sweeps higher and higher, definitely wrong but quite exciting

Anyway, need to get the WG off and changed and see what its like then. It is the original one AFAIK with over 200,000 miles on it Theres quite a bit of play in the valve guide and this is in effect a boost leak although I guess its supposed to be a known one and so can be mapped for. If you had a leak like that elsewhere in the system it would be a problem I'm sure.

[S2central.net]

See this video...

http://uk.youtube.com/watch?v=FJ_W6g04xso

Tis in German but seems to show an S2 WG under test with a 1.9bar spring... Cracks open ~0.5bar BOOST and full open 0.9bar boost.

[S2central.net]

Sorry - confusing myself here tonight with your recent posts about tests at lower pressures...

I remember attaching an airline onto the lower chamber of a perfectly good RS2 WG and was amazed at how much air it leaks into the escape chamber.

It was long ago and I remember speaking to Mihnea about it way back then - he assured me it was nothing to worry about as they all do this - the design is not supposed to be airtight - even though your gut tells you it should be.

Trouble is how much blowby is OK and how much is not ?

Only three things can keep your WG closed if the ECU is not involved...

1. The WG valve is sticking - sticking shut that is
2. There is insufficient air pressure getting to the lower chamber to open the valve (checked that line and/or WGFV for leaks ?)
3. The diaphragm is leaky and/or there is excessive blowby from lower chamber into the escape chamber

Does that make more sense ?

[newsh]

Too much boost Paul, it would have to be sticking closed or not opening enough..

I've had the thing apart, the diaphragm is good but there's quite a bit of play in the valve guide. Could be enough that the lower chamber is leaking down into the exhaust.

[S2central.net]

Smells like WG valve is sticking open...

Assuming your diaphragm (and upper chamber) is airtight you can use a vac pump to suck the WG valve up and off its seat... Then when you quickly release the vacuum from the upper chamber you should hear the WG valve make an audible clunk when it is pushed back onto its seat.

[newsh]

I think you may be right, only one way to check, so will be putting a new WG on.

[Jonas_R]

I think it is leaking between lower and upper part, or atleast leaking from the lower part because:

The more boost you make the more pressure you will apply to the lower part of the wastegate and thereby pushing the piston upwards in the wastegate which will then make air go through the wastegate instead of the turbo. If you cant get it to hold mechanical boost, then you can't have an airtight lower part of the wastegate.

[newsh]

This is with N75 bypassed.

[Jonas_R]

Right chaps, just did the stock spring experiment, i now have only 0.5 Bar of boost through the midrange rising at 4k5 to 2Bar at 5k. So the spring is definitely not controlling the high rpm boost.

Ross, I think you're right theres an issue here. Either the WG is closing at high revs or not flowing enough for some other reason.

Jonas, yes, 1 Bar of boost is 2 Bar atmospheric, springs are sold calibrated in atmosheric or "absolute".. can be confusing.

Well I would suspect that your wastegate is leaking between lower and upper chamber or perhaps you got a sticky N75, or was this tried without the N75?

[Rusty]

Something is a bit fishy there. You're only producing 0.5bar boost so the gas flow shouldn't be that great, certainly less than with an RS2 turbo at 2 bar gauge. Thus, with no WG control the boost should not rise, the WG should flow well enough.

IDEA, what if the pipe after the WG is blocked? Is defo worth trying another WG in there too.

[Jamo]

New wastegate time

[Greg_S]

Could it be that the valve in the wastegate is bent or sticking?

[newsh]

Right chaps, just did the stock spring experiment, i now have only 0.5 Bar of boost through the midrange rising at 4k5 to 2Bar at 5k. So the spring is definitely not controlling the high rpm boost.

Ross, I think you're right theres an issue here. Either the WG is closing at high revs or not flowing enough for some other reason.

Jonas, yes, 1 Bar of boost is 2 Bar atmospheric, springs are sold calibrated in atmosheric or "absolute".. can be confusing.

[Ross]

Suspect there's an issue here - I drove my 3B with the GT3071R on a custom MRC map to 1.5bar (for the K24). It was overboosting to 1.6bar in the mid-range as the ECU struggled to reign in that mighty efficient beast of a turbo, but it did bleed off boost near the top end. The point is, with a very similar set-up my stock WG had no problems handling it. An unmentionable person demontrated mechanical boost to me on my Avant with the GT3071R, set to 1.9bar on the spring, yet it was spiking & overboosting something crazy. My conclusion was to get it ECU controlled.