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Old 04-26-2004, 09:33 PM   #1
heffergm
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Default Intake silencer delete fluttering noise

A few weeks ago I removed my intake silencer. After doing so, I took the car for a drive, and noticed that under full boost, I got a really loud "flapping", or fluttering sound.

I figured it was the rubber seal around the hole leading into the airbox that was now "flapping the breeze" so to speak.

So, I decided to hack up my silencer, and I created an elbow so that everything fit together like stock at the airbox, and air would be pulled from the fender well.

However, tonight I noticed the sound again... same fluttering at full or near full boost. Not as loud as without my snorkel modification, but there none-the-less.

Any ideas as to what it might be?
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Old 04-26-2004, 09:41 PM   #2
MB38
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The sound is compressor surge. What blowoff valve did you put on your car?
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Old 04-26-2004, 09:42 PM   #3
heffergm
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It's not the BOV... especially given the fact that I don't have one. I'm running the stock recirculating valve. The motor is completely stock.
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Old 04-26-2004, 09:43 PM   #4
MB38
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Sorry, just an assumption. It still sounds like compressor surge to me, though. Do you have a camera that can capture audio of it to confirm?
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Old 04-26-2004, 09:55 PM   #5
04Scooby_Rex
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it is probably wastegate flutter, when the wastegate opens to bleed boost, the exhaust going around it can make the flap move around. it will then make the noise you heard. do a search for wastegate flutter.
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Old 04-26-2004, 10:03 PM   #6
03WRX83
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its normal man. Wait till you get a dp on.. its get louder.. then once you get the uppipe, and catback exhaust its even louder. Its normal sound of the wastegate.
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Old 04-27-2004, 01:10 AM   #7
blarg
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when I got my WRX I noticed that sound too and after reading all the stuff on the various forums I was afraid it might be compressor surge...I even took it to the dealer several times.

As it turns out it IS normal and its the wategate noise. Its actually a very muted and muffled version of the noise most people are looking for when they get their BOV....it the noise in all the movies and all the rally videos. Of course in those cases its dumping the wategate gasses to atmosphere, which is illegal for highway use, but it does get noticable at you remove more and more cats. Also - if you really like that sound, get a THINNER walled DP...that's bring out the noise even more.
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Old 04-27-2004, 01:37 AM   #8
MB38
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Wastegate flutter only happens at full boost, when the wastegate is open. When you come off the throttle, you instantly go into vacuum, slamming the wastegate shut. If you heard ANYTHING during shifts having to do with your wastegate, it would be a slapping noise one time. Wastegate flutter sounds like exhaust flatulence... like your car is ripping ass. If you've ever been next to a semi truck when it goes full throttle, you've heard this sound on a much larger and louder scale. It sounds like a flapping exhaust farty noise that's loud enough to startle those close by.

Unless something has mysteriously changed with the laws of physics or the concept of a wastegate, what you are hearing has nothing to do with the exhaust side of the turbo.

If somebody knows more than me, correct me, but I'm about as sure as I can be about this, all from first-hand experience.
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Old 04-27-2004, 01:45 AM   #9
MB38
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This is an Apple Quicktime sound clip of compressor surge on an STi. Somebody else posted this a while back, I moved it to my webspace for future reference. This is fairly decent compressor surge. If what you hear sounds anything like this, then we're talking about surge. If not, I'm way off target.
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Old 04-27-2004, 06:55 AM   #10
heffergm
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Nope, that's not it. The noise in the clip is flutter between shifts, at least as far as I can tell.

I get a noise (and it doesn't really sound quite like the noise in the clip) that occurs while UNDER full boost (i.e. foot to the floor).

Last edited by heffergm; 04-27-2004 at 08:10 AM.
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Old 04-27-2004, 05:18 PM   #11
MB38
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In that case, I retract all of my previous statements, I must have misread the post. I assumed that it was in between shifts, not at full boost. What you are hearing is, indeed, wastegate flutter.
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