Understanding BPV Flutter - Subaru WRX Forum
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#1 Old 10-14-2013, 09:36 AM
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Understanding BPV Flutter

So I'm looking for some insight and opinions/facts from people I know rather than don't on this topic, and didn't see any links pop up on the subject here or on google. I also know each situation is very different with this subject so that's why I created my own thread. But here's my story...

Was doing a 390m road trip into the mountains yesterday and I started to feel a flutter associated with my BPV. It seemed to only do it while shifting into 4th at high boost (16-18psi) but didn't really test it out at lower boost to see if it was only happening at high psi (didn't think of it). After reading threads about this subject this morning I now know low/high boost flutter can mean different things...so maybe more testing will need to be done.

But this was not under WOT shifts...more like 70% I'd say. I did testing in 1st and 2nd under the same boost/throttle levels and didn't hear any flutter though if this helps diagnose things.

Sooo...Any idea why?

What exactly makes the "flutter" happen? A leak of sorts?

I read this AM that cold weather changes can cause this with no other reason/problem. True? It was probably low 40's in the AM, but it still did it in the PM when warmer around 55 degrees so I doubt mine is temp related.

Should I try a different spring?

Can elevation change cause this?

What is the difference in a wastegate flutter and a BPV flutter? How can I tell the difference?




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#2 Old 10-14-2013, 04:08 PM
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I don't know much about it or have anything usefull to add but, when i was getting my tune done the first wastegate spring set-up my tuner had me run was either fully open or closed depending on throttle and boost. He had me change springs and now it's either constant flutter or closed depending on throttle and boost. It sounded much better without flutter. I asked if it was supposed to have a constant flutter and he said yes, its normal for many. Sure miss the fully open sound though.
Im guessing flutter is spring dependant based on this, although Im sure there are some more factors too (boost, throttle, boost control system, exct ...).
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#3 Old 10-14-2013, 07:26 PM
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Sounds like surge to me...

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#4 Old 10-14-2013, 07:29 PM
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Quote:
Originally Posted by psinuse View Post
Sounds like surge to me...
Can you school me on this Keith. I def have next to no experience with FI systems/terms.

I found this link with a half way laman explination, but I'm still trying to understand it....

http://forums.hybridz.org/topic/7758...nation-within/

So what causes this?
Tune related/fixable?




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#5 Old 10-14-2013, 07:55 PM
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I know the audio quality isn't the best, but this sounds exactly like mine!

http://youtu.be/03Hk1hIx4A4


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#6 Old 10-14-2013, 08:05 PM
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Here's another link of what mine is also doing. I didn't notice it in every gear though, just shifting into 4th.

Is the fact I only hear it in one gear a sign it's this or that?.?.

http://youtu.be/jEUWEsqoWz8

I just watched a bunch of "compressor surge" videos too and mine def didn't sound like that. That sounds horrible!


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#7 Old 10-14-2013, 08:28 PM
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This is suppose to be an authenticated video of compressor surge. The flutter is happening WHILE accelerating, as to where mine is happening after I let off the gas and shift gears. Is this a sign that I'm experience just BPV flutter?.?.

Need help guys!
http://youtu.be/nCj6Spwl1CU


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#8 Old 10-14-2013, 09:34 PM
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Are you getting any CELs at all? Compressor surge happens when you don't have enough air flowing out of your BPV and it flows back into the turbo going the opposite direction as the air coming in. Maybe your PBV isn't opening all the way.

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#9 Old 10-14-2013, 09:46 PM
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Blow Off Valves (BOV) & By-Pass Valves (BPV)

By-Pass Valve - does exactly what the name suggests. when you let off the gas and the throttle closes, the BPV opens to BY-PASS the turbo and send the air back to the intake. This has 2 benefits...it prevents compressor surge and at the same time utilizes that pressurized air to keep the turbo spooled when shifting.

Blow Off Valve - Blows off air to atmosphere at throttle lift. Bad for MAF based vehicle since you are releasing air measured by the MAF...this makes the car run rich and blow fireballs when shifting. BOV's only prevent comp surge and the turbo will slow more while shifting compared to a bpv since the air isnt recirculated to keep the comp spinning.

In both cases when you lift of the throttle the pressurized air now takes the path of least resistance.....if you put a 30 psi spring in your bpv and you're running 20psi and you let off the throttle....the spring is going to be too tight to open so the air has to go somewhere....which is through the compressor backwards. Thats compressor surge. You're shoving air through the compressor backwards.

BPV's and BOV's dont do anything at WOT...unless they are leaking. Their main functions (preventing compressor surge and utilizing the pressurized air to keep the turbo spooled while shifting) happen when you let off the gas.

I recommend the forge race bpv with spring kit or a Tial bpv with spring kit. The spring kits add adjustbility that stops them from leaking at idle. The HKS SSQV is the worst valve on the market...stay away at all costs.
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#10 Old 10-15-2013, 05:10 AM
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You do realize that all BOV leak?

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#11 Old 10-15-2013, 05:38 AM
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Quote:
Originally Posted by boo-key bear View Post
Blow Off Valves (BOV) & By-Pass Valves (BPV)

By-Pass Valve - does exactly what the name suggests. when you let off the gas and the throttle closes, the BPV opens to BY-PASS the turbo and send the air back to the intake. This has 2 benefits...it prevents compressor surge and at the same time utilizes that pressurized air to keep the turbo spooled when shifting.

Blow Off Valve - Blows off air to atmosphere at throttle lift. Bad for MAF based vehicle since you are releasing air measured by the MAF...this makes the car run rich and blow fireballs when shifting. BOV's only prevent comp surge and the turbo will slow more while shifting compared to a bpv since the air isnt recirculated to keep the comp spinning.

In both cases when you lift of the throttle the pressurized air now takes the path of least resistance.....if you put a 30 psi spring in your bpv and you're running 20psi and you let off the throttle....the spring is going to be too tight to open so the air has to go somewhere....which is through the compressor backwards. Thats compressor surge. You're shoving air through the compressor backwards.

BPV's and BOV's dont do anything at WOT...unless they are leaking. Their main functions (preventing compressor surge and utilizing the pressurized air to keep the turbo spooled while shifting) happen when you let off the gas.

I recommend the forge race bpv with spring kit or a Tial bpv with spring kit. The spring kits add adjustbility that stops them from leaking at idle. The HKS SSQV is the worst valve on the market...stay away at all costs.
Where'd you get this from Adair?


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#12 Old 10-15-2013, 05:44 AM
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Quote:
Originally Posted by psinuse View Post
Are you getting any CELs at all? Compressor surge happens when you don't have enough air flowing out of your BPV and it flows back into the turbo going the opposite direction as the air coming in. Maybe your PBV isn't opening all the way.
No CEL at all. How can I definitively tell which one I'm getting? And how can I fix it?

I plan on taking my BPV off this weekend and re-sealing things with RTV and was thinking about trying a different spring.

I know I have 2 shims in and the yellow spring at this point as that's what wa suggested to me by my tuner. Any recommendations on what different setup to run? Forge's website says the yellow spring is good from 15-23psi though...

http://www.forgemotorsport.com/conte...roduct=FMDVTUN

So how do I fix this?!


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#13 Old 10-15-2013, 06:12 AM
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Quote:
Originally Posted by the RIOT act View Post
Where'd you get this from Adair?


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My tuner.

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#14 Old 10-15-2013, 06:16 AM
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I'm gonna email my tuner now. I need to know whether this is def surge or flutter and how to fix it...


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#15 Old 10-15-2013, 06:22 AM
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Quote:
Originally Posted by psinuse View Post
You do realize that all BOV leak?
Honestly, I don't know if they all do or not. I've heard they do and then again I've heard some don't. I would like to believe there are some out there that don't.

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