[skark_burmer]

I was running a cobb stage 1 tune with stock downpipe and didnt notice the noise, but when i went to a stage 2 tune and one of their downpipes i am hearing a noise i would classify as "not right".
Im new to the STI world but am a rather competent mechanic, with that being said it sounds as if the wastegate is bleeding off pressure making a fluttering noise at partial throttle.
At about 1/4 to 1/2 throttle i'll hear the noise, but when i get deeper than 1/2 throttle, the noise goes away.
Mostly this happens around 2.5 to 4k rpm, i dont partial throttle past 4k.

My 08 is fully stock other than the tune and downpipe, 5k miles, 150 with the stage 2. No boost gauge so im not sure what im boosting.

Any thoughts?
I also have an e-mail in to Cobb, i'll post their reply if they offer insight.

[Savarak]

use the ap's live feed to find your boost

[Shag-e]

Could it be that you are hearing the stock BOV (blow off valve)? I know that when I ran a DP on my legacy you could hear it when I lifted.

BOV was my first thought.

[waktasz]

Have you ever driven someone else's car with a bellmouth downpipe? What you are describing sounds normal to me.

[fullerton]

fluttering wastegates are not a problem.

[96accord]

Mine does that on my 07 wrx (stage 2).. it's normal

[skark_burmer]

Originally Posted by fullerton

fluttering wastegates are not a problem.

Are you sure? (Thats a question, not a statement.)
my past experience with turbos (aircooled porsche's, no subie experience) says that the wastegate should be closed when on the throttle. When accelerating the wastegate should be firmly closed and not letting the partial boost push it open. In stock 911's the vacuum applied to the wastegate at full throttle/low rpm isnt enough when running a race exhaust so a additional spring or a vacuum accumulator is required on the wastegate actuator.
Im thinking i am having the same issue with the Cobb downpipe, the new exhaust has much less backpressure so the wastegate is being slightly overpowered as compared to a stock setup, being sucked open slightly.
While not a engine damaging issue, i dont think its right.

I have been doing reading on past years STI's and fluttering wastegates are common when mods are done. The earlier cars had a adjustable nut you can move, although if you go too far people are reporting boost spikes. I expect the 08 has the same adjuster nut, but i cant see cause i re-installed my heat shield and it covers the area in question. Hey, it was late last night, i'll peek this weekend.
Although if i do have the adjuster nut, im not going to fiddle with it till i get a boost gauge, or i hear back from the Cobb folks as im not sure that is the best solution.

[kts262]

Originally Posted by fullerton

fluttering wastegates are not a problem.

+1, it's wastegate flutter. it's normal to hear on a freer flowing downpipe, especially a bellmouth and it's nothing bad.

[fullerton]

The adjuster is not on the STi's VF34 or newer turbos. It is on the WRX's turbo.

There is a certain boost target for a set rpm/load that your car is tuned for. If you are creating more boost pressure than the set level, it has to go somewhere or you overboost. The wastegate is simply fluttering to keep you within the levels the computer has been programmed to meet.

[skark_burmer]

Originally Posted by fullerton

The adjuster is not on the STi's VF34 or newer turbos. It is on the WRX's turbo.

There is a certain boost target for a set rpm/load that your car is tuned for. If you are creating more boost pressure than the set level, it has to go somewhere or you overboost. The wastegate is simply fluttering to keep you within the levels the computer has been programmed to meet.

Ahhh, that makes sense. I figured the actuator was more than strong enough to make up for the exhaust change.
Super sweet, thanks man.

[vmaxlvrs]

OK, a lot of this went over my head ,........i will be going to a tbe in the very near future is this flutering preventable what would need to be dont to eliminate this from hapening?

[mofoSTI]

Its normal.

[skark_burmer]

Originally Posted by vmaxlvrs

OK, a lot of this went over my head ,........i will be going to a tbe in the very near future is this flutering preventable what would need to be dont to eliminate this from hapening?

From what i gather (anyone feel free to correct me if im wrong) the fluttering is supposed to happen. Apparently the turbo is creating more boost than the computer thinks is ok and therefore the actuator is allowing the wastegate to open slightly to bleed some off. This is also happening on a stock car, you just dont hear it.
With a TBE you have less backpressure so more fluttering is evident, also the aftermarket pipes make the noise seem even louder.