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Andy, its not a spring thing, it does adjust peak boost but its still double what it should be at high rpms.
Spoke to Doug at MRC, he said something is definitely wrong, it should come up to whatever the mechanical boost is set at by the spring then stay there as it revs out. It should not keep rising and end up at 2 bar on a 1 bar spring. This means the WG is not controlling the boost which he would normally only expect to see on a bigger turbo like a 35R, not a 3071.. He suggested I pipe the turbo pressure side straight into the WG to check the WGFV is not leaking, which I've done and its no different. He also said it can be caused by an exhaust thats too good, ie not enough back pressure and suggested I try running with a baffle in the tail pipe to simulate more back pressure. I may well do this tomorrow when I can work out a method..
Or maybe my Wastegate is just worn out?
Well, its probably a 1.9 bar spring but what I mean is its set for 1 bar of boost, on the old RS2 turbo it would give 1 Bar at anything less than WOT. At WOT the WGFV would upp the boost to about 2 Bar.
Today I'm going to put a stock spring in to see if it makes any difference.
@newsh
To little back pressure seems unlikely, Iam running 3" exhaust turbo back and no cats, no middle silencer etc. and the wagner EM. Does seem to me that your lower part of the wastegate is leaking into the upper part. This would cause high boost since the the wastegate stays closed.
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.
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.
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.
Cheers'en, AndyC
1994 ABY Coupe - Projekt Alpinweiss
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?
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