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Discussion Starter #1
I removed the snorkus a few days after buying the car in November so I can't honestly say if I was hearing this sound before but since then...

At right about the transition from vacuum to boost I get a hissing sound that sounds almost hydraulic. Doesn't matter if the pressure's on its way up or down. The range is pretty narrow: about -.5psi to +.5psi MRP and I can keep the sound going by keeping the boost right at 0psi. It's not the recirc/relief valve. I can make that pop by letting off the gas abruptly after heavy boost and it doesn't sound the same.

Any ideas?
 

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2016 Forester XT
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That's probably exactly what it is though, many FXT's get a bit of wastegate flutter in that exact pressure range for the same reason. It's totally different sounding than when it dumps...
 

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brett s said:
That's probably exactly what it is though, many FXT's get a bit of wastegate flutter in that exact pressure range for the same reason. It's totally different sounding than when it dumps...
I was thinking the same thing.
Mine became much more noticeable after I did the snorkus removal too.
Being a retired teamster, the sound kind of reminds me of my old Mack CH613, just a little softer.
 
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So what's the state of that valve with the engine running at idle or low RPM? Open?

If so, then as the turbo starts to spool up I guess I'm hearing it pressurize the manifold and as soon as the pressure builds up enough to close the valve actuator, the external noise stops. It'd be the same as the turbo slows down. It's still supplying pressure but not enough to keep the valve closed so I hear the noise until the turbo slows down enough.

Yeah?
 

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2006 RX8
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Mine started doing it immediately after upgrading to an ITG filter and doing the Snorkus removal. All of my hoses were tight and airbox secure. It a whistling kind of noise and its pretty annoying to me. I have had CAI's cause that kind of racket in the past, but not a modified air box. I did the same kind of mod years ago to my WRX air box and don't recall it being noisy like my Fxt. It bothers me enough at times that I have considered replacing the snorkus.

As far as what it is, I think its simply the air drop and vacuum noise as the turbo starts to spool-up. With the snorkus in place the air draw is much more indirect and baffled, which I think muffles the noise.

Bottom line is that you are not alone! :wink:

Jeff :)
 

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Subaru call it a "resonator" but it seems more like a de-resonator. The noise is always there (a kind of hiss) but until you remove the "resonator" the noise gets suppressed.
I did the same on my previous Imprezas and got the same noise as on my S Turbo so I'm relaxed about it.
It has also "amplified" the BOV - but not as loudly as the I had one that vented to atmosphere which made people look and old ladies faint. My defence was it was fitted in Japan before I bought the car.
 

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BLUE WASABI, (#2 Info Provider)
2008 SG Model D
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I love the sound...I wouldn't mind having a scary BOV sound to startle people but having an atmospheric BOV will only be detrimental to my performance w/ my current power level.
 

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it sounds to me like you are describing the sound of the waste-gate opening to bypass the impeller. The way I understand it is that the wastegate is closed until the target boost is reached, then the waste-gate actuator opens the waste-gate to bypass boost around the impeller to keep the compressor side from building more boost.

I wasn't as pronounced untill after I removed my snorkus either.
 
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Discussion Starter #12
oldgit said:
N10S said:
Sort of like the bad guys in the movie that put a snorkus on their pistol?
Its about the only use I can think of for the thing :lol:
Maybe we can have a contest...

"Creative things you can do with your snorkus"
 
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Discussion Starter #14
sirwilliam said:
Mod it and use it as a CAI.
I was thinking of that. Just chopping off the part that returns into the engine compartment. Right now I've got a short piece of 3" flexible aluminum duct stuck into the airbox just to keep water from splashing on the underside of the filter.
 

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Harbor Fright
2005 XT
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Running with the snorkus removed can be a little loud... and while opening up the throttle response and top-end a bit, the torque seemed to suffer. Fortunately, that went away with the Stg. 2...

After experimenting with in-fender intake tracts using all kinds of ducting and plumbing parts (PVC pipe & fittings, various rubber donuts), I have settled on one plumbing part: not sure exactly what it's called, but it is the inner rubber piece from a 3" to 3" clamp designed to join two PVC pipes together (found at the local Home Center). It looks like a band of corrugated aluminum with two worm-type screw clamps riveted on (maybe ~$5-6?).

I have taken it apart and turned the rubber piece inside out and fitted it through the fender hole into the airbox (the stock inner ring on the airbox also removed, leaving the opening >3") - there is a ridge around the center of the rubber (again, when turned inside out) that holds it in place when located between the airbox and fender wall.

The goal here was max air volume entering the airbox while smoothing the incoming flow, but keeping the resonances, etc. out of the engine compartment. So far so good- it's been on there since August. It's quiet on the prowl, but barks when stepped on. :twisted:
 

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JDM Foz [sold]
2016 Mercedes E220 AMG Auto
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I take it you guys mean your getting a hiss noise on acceleration and a pssst noise when you ease off the accelarator?

I removed the stock air box and filter and replaced mine it with an open air filter, similair to the K&N 57i filter.

When you put your foot down you can hear the air being sucked into the engine, and when you take your foot off, if the revs are over 3500rpm you get the same noise as a BOV and it is quite loud. There are two tunnels about 3/4 mile long near my home and travelling through those my mate who was travelling behind me could hear when I lifted off and you get the PSssst! noise.

mike
 

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2004 Forester XT
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RemyJ said:
I removed the snorkus a few days after buying the car in November so I can't honestly say if I was hearing this sound before but since then...

At right about the transition from vacuum to boost I get a hissing sound that sounds almost hydraulic. Doesn't matter if the pressure's on its way up or down. The range is pretty narrow: about -.5psi to +.5psi MRP and I can keep the sound going by keeping the boost right at 0psi. It's not the recirc/relief valve. I can make that pop by letting off the gas abruptly after heavy boost and it doesn't sound the same.

Any ideas?
The noise is likely a leaky bypass valve. It's not the air being sucked in, because the hiss only happens (on mine anyway) at part, but heavy, throttle. If I "floor it" the hiss goes away, even though there's even MORE air getting sucked into the engine.

The bypass valve is designed to open when more pressure is on the turbo side of the throttle body than on the engine side (throttle slammed shut, for example.) Unfotunately at part throttle the pressure on the engine side isn't high enough relative to the turbo side to keep the valve closed, so it leaks. Once you go WOT, that problem goes away.

Mitu Eclipse bypass valves suffer from the same problem, and frankly look to be almost the exact same design. Crushing the mitsu valve SLIGHTLY put more spring pressure on the valve and helped the leakage, I've been tempted to try it on the Subie, but haven't gotten around to it.

Jack Zhe
 
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Discussion Starter #18
Zhe Wiz said:
The bypass valve is designed to open when more pressure is on the turbo side of the throttle body than on the engine side (throttle slammed shut, for example.) Unfotunately at part throttle the pressure on the engine side isn't high enough relative to the turbo side to keep the valve closed, so it leaks. Once you go WOT, that problem goes away.
Yep, that makes sense, thx.
 
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