Compressor surge has nothing to do with blow off valves or lift off flutter!

Compressor surge is caused by the turbo going outside it's flow capability at a given shaft rpm, causing the compressor to aerodynamiclly stall.
(It's been said that a slightly more restrictive intake pre-turbo will supress any surge)

It can happen at low shaft rpm (as in my above vf34 video) as the turbo is starting to produce boost (hence a similar sound to lift off flutter).

I can induce it in my own car by lifting off slightly as the boost peaks & trust me seeing your boost gauge needle vibrate wildy between 10-24 psi is concerning. The sound is like an abrupt chirp or squeek along with a cough from the engine.

It's dangerous because:
1. the compessor & turbine wheels are getting shock loaded at 100,000 + rpm
2. the pressure surge inside the engine can cause catastrophic detonation in a single cylinder
3. it shock loads the engines bottom end
4. it plays games with map sensed ecu's

As Jungleboy said, it can be tuned out by lowering the target boost value at the surge load/rpm point.

Mine gets transient surge at 80-90% throttle opening at around 4000 rpm @ 1.65 bar, foot flat or <80% and it doesn't happen. I think 1.7 bar on my vf29 is pushing it beyond it's capabilities a little

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incorrect.

What you are describing is just flutter when you come off the throttle. Its generally not a problem.

Actual compressor surge happens at full throttle when the engine cant swallow the air as fast as the turbo is pushing at low rpm. Usually it happens as the turbo is building up boost at low rpms. It causes shock waves to flow backwards through the intake tract and turbo while the air is still flowing forward through the turbo. Thats where the chu-chu-chu noise comes from at full throttle. Very bad for the compressor blades. You get rapid fluctuations in boost pressure that the ECU hasn't accounted for which may cause a lean out and kill your engine too.

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RS Liberty - Because WRX's are only good for parts...

P.s OP: An SSQV is blown shut under boost, it can't leak.....That's the beauty of it's design.

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Well I took the car for a spin last night and I can easily cause the sound to occur in fifth gear. As the boost builds at full throttle and spikes at 1.5bar it will flutter a little then hold around 1.2bar. Sometimes occurs on 4th gear.

Good news to hear it can be tuned out once I get the verso tune. I'm not sure if replacing the boost solenoid for the tune will be an advantage at my level of modification. Guess I'll take it easy till I got enoungh cash for a tune.

Thanks for all your help, Anthony

Solid boost control is always a a good idea, get a 3 port boost control solinoid fitted, they aren't expensive. If you plan to mod in the future or run boost in the 1.3 to 1.8bar range it all helps.

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K.E.R.S!!!1

Is your noise more like the one in this vid?? http://www.streetfire.net/video/2006...htm#commentTop
Apparently that is wastegate flutter and is normal (very different cause and effect to compressor surge)

See here:http://forums.nasioc.com/forums/show...hlight=wastega

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MY99 WRX (Sold)
MY06 WRX 241hp 430nm atw (Sold)
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AUDM heads are small.. hence the flutter. Solution = lower boost.

JDM heads are bigger and ported, put that on and problem solved = $$$$$$

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GO APR

Maybe, it doesn't really happen in any gear other than 4th or 5th when cruising along. Makes the sound for about 3 seconds or so as it's building onto boost.

Has done it since the 34 went on. Didn't do it on the TD04 with the same downpipe. Has been on the same Verso tune for a few years now with this 'problem' with no adverse effects.

This is with 20psi - Suspect blommer may be right about the heads.

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Should have bought an STI

there's a reason why VF35 is used as a standard turbo for the AUDM GDBs. It has a smaller compressor wheel and had P15 housing as compared to the VF34. AS the AUDM heads are smaller, the amount of air entering is restricted, thus creating the flutter. Upboosting the VF35 will also cause fluttering as there's only 1bar or so of boost the AUDM can take in efficiently.

Whereas the VF34 came standard on JDM GDBs because it had bigger ported heads to complement with it.

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GO APR

i don't get any sort of "flutter" and im running a vf34/p20 @ 20psi on my audm my04 wrx.