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I may have mentioned in one of my other posts about a noise coming from my car after the motor swap....and just didn't know what it was.....

Well, I had some friends with subaru turbos ride with me last night, and they're pretty sure it's wastegate flutter. You hear it mostly when initially building boost, especially if I'm in 4th, low rpms, and then give it some gas. As RPM's climb, I don't really hear it much, but it's probably still there. They did however mention that it didn't sound too bad, at least compared to his forester.

I remember Vikash mentioning something about STi guys having wastegate flutter or some issue with the waste gate after switching from the stock down pipe, due to the increase flow, and lack of back pressure around the wastegate.

Those of you with either the CES system, bell mouth, or some other aftermarket down pipe, have you experienced anything like this?

I expirence a similar sound. I have a 3in DP with stock STi catback.
Mine sounds like a fluttery noise at around 0-5psi then it stops.
It sounds more like compressor surge to me. Which is caused by the compressor making boost before it is designed to. Do you have a MBC?
When I used the factory boost controler, boost built slower, and I didnt have the noise.

just some thoughts

I'm hoping to have my boost gauge in by the weekend. Once I get it in, I'll be able to see a little better what's goin on when.

Nope, I don't have a MBC, everything's stock as far as boost control and such.

Maybe you should try using a wastegate helper spring to help hold the wastegate shut.

I haven't had any problems with my exhaust or turbo.

If it happens when you build boost, it sounds like your wastegate may be fluttering because the wastegate actuator is unable to keep the wastegate shut.

It seems that most VF turbos have issues like this, with relatively weak wastegate actuators.

A spring, similar to the spring on the clutch fork, would help keep the wastegate shut when it's supposed to be.

Yeah my buddy recommended replacing the spring, but due to the fact it's a sealed unit, I really didn't know how to change it.

I can try playing around with a helper spring. At least I'd hopefully be able to correctly identify that it is truly wastegate flutter and not something else.

I do have other wastegate solenoids. I could play with them and see if either of those require more force to open then the others.

Don't fuck with replacing the internal wastegate spring. Just add a helper spring.

You can use almost any wastegate actuator from a Subaru turbo. So one from a VF39 or a TD04 would also work.

I was talking about STi guys getting boost creep when they upgrade the exhaust, not wastegate flutter. That happens because the STi's turbo is goofy -- a big cold side and a small hot side. I don't think it's a concern here.

Putting another spring in parallel with the wastegate actuator's current spring will throw off boost control; I don't know if the stock ECU will be able to figure it out. If you want to try it, though, look up my "40-cent boost controller:"

http://www.graphics.cornell.edu/~v/pics ... legacy.jpg

So you added the spring??

Wouldn't the ECU compensate by decreasing the PWM of the solenoid feeding the wastegate actuator?

I've added a relatively light helper spring, and the ECU was cool with me making 10 psi because of it. I've been meaning to readjust it now that I've added the intercooler, so I can get back to 10.

Yes, I added that spring in order to raise boost levels.

The ECU may be able to compensate for the change by decreasing duty cycles; I don't know whether or not it would be within its range of flexibility.

Is your foot fully on the gas or just holding a constant rev?

If have a constant rev at around 4000rpm or up you will be generating boost pressure but have vaccum in the inlet manifold cusing the blow value to open slightly.

Could just be the sound of air passing out the blow off value?

I dunno, just an idea. This would explain why it stops when you put ya foot down and accelerate.

I will also add I do get some flutter, but I'm running a Brullen 3" bellmouth. Part of it sounds like the wastegate simply doing its thing, but the sound is amplified by the big downpipe, so that its noticeable.

The noise I'm hearing is under full throttle (foot fully to the floor) and is most noticable if I'm in 4th around 2-3k rpms, and floor it. Boost will build, rpms will go up. I don't hear the noise when rpms get past a certain point. I either just can't hear them, or they stop.

Mike, you may be right, it may just be doing its thing....I don't know.

I pulled the wastegate actuator off. It's fine, and tension is on the wastegate valve when it's just sitting.

I did find some other interesting things. There was a fair amount of soot on the shaft of the wastegate flapper, the one that comes up. So it's probably leaking exhaust gasses there. Which could contribute to the noise I'm hearing.

Also, when I removed the wastegate actuator, there was oil on it. The compressor is not sealed, and is leaking oil either from oil coming in through the PCV system, or seals.

Either way, I'd say this turbo is not in the best of shape. It's also another reason to get a catch can.

Other odd thing I noticed was that the wastegate control duty % read by the ECU is 1.6% at idle. The FSM says it should be 70% at idle.

hmm well i have a 3" ETS bellmouth DP and stock STI catback, and at part throttle, right around 10 vaccuum to 2psi it makes a weird sound, almost sounds like a supercharger. like a whining noise, but at full throttle is goes away to the turbo whistle. think this is the same thing? (i was running the turbo on wastegate directly from the compressor at that time) it may be different now that i swapped ECU's and got my stock boost control)

also at full boost with that setup i got crazy boost creep... wastegate should be around 6psi, it would creep up to 9 or 10 sometimes

Your issue may sound like something similar.

As for boost creep, I may have gotten an overshot of 1-2 psi, but I'm not sure because my boost gauge is tits up right now. I'd have to have someone watch the select monitor to verify.

my flutter does not come from full throttle. It's between 0-5 psi and under very mild throttle(like holding speed going up a hill). I get no boost creep.

Boost creep FTL


They are right about the wastegate flutter...It just sounded a lot like detonation...


Vikash is right about running a RRFPR and not running bigger injectors...and RRFPR's are cheaper than injectors...which is nice...

LaureltheQueen wrote:my flutter does not come from full throttle. It's between 0-5 psi and under very mild throttle(like holding speed going up a hill). I get no boost creep.

Yeah mine is very similar....is reproducable in light throttle circumstances around the same pressures or until rpms rise.

mine was at any rpm, worst down low though, and any time i went part throttle right around 0psi/vac is when it would do it the worst.

now that i got it driving on the correct ECU, ive noticed some CRAZY wastegate flutter and realize what you guys were talking about. because its a bellmouth, 3", and no insulation, i can hear it when it builds positive boost, and its just as loud or louder at WOT after it pegs at 9psi.

im glad to hear its not detonation, because for a moment i had no idea, no one ever said if this is harmful in any way..?

also now on stock boost control, i dont get boost creep, maybe just 1psi, but under 10

No it's not harmful, but it does rob power.

LaureltheQueen wrote:my flutter does not come from full throttle. It's between 0-5 psi and under very mild throttle(like holding speed going up a hill). I get no boost creep.

my car is the same way. i do have a bellmouth downpipe on it.

Can you descibe the sound? I get a small pulsation through the driveline when I'm in fourth realatively low rpms. I'm wondering if what I'm feeling is what your hearing.