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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 03-08-2013, 06:11 PM   #1
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Have I got compressor surge ?

Hey there guys,

For those that don't know my turbo is a G-pop shop big T-28. I usually run 13lb base boost and spike around 27-28lb boost.

Now this noise I'm talking about has allways been there, since day one of this turbo.

The noise is this:

In 3rd and 4th gear wot pulls you can hear the turbo whistle sucking as the car revs higher and higher, then when it's in the full boost range the turbo whistle seems to "flutter" a bit, under boost,full power.

Now the car always revs cleanly and never coughs or farts when this "flutter" noise happens. The engine never misses.

In this video I have backed my boost way off. Base boost is like 10lb and spiking at 21 lb but still making the fluttering noise at full boost .....WTF?

Turn the volume up and try to focus on the turbo whistle in the background. You can hear it sucking cleanly then flutter at full boost.

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Old 03-08-2013, 06:17 PM   #2
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Sounds like an issue with a vacuum hose or turbo bypass valve.
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Old 03-08-2013, 06:26 PM   #3
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What's the turbo by-pass valve ?
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Old 03-08-2013, 06:32 PM   #4
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Connects to the intercooler to throttle body pipe. Has a single vacuum line running into it. I dont know what setup you have, but its either a turbo bypass valve or blow off valve.
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Old 03-08-2013, 07:02 PM   #5
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Lolz, you mean the BOV ?

Out of curiosty I'm out in my garage testing my BOV now.

Does the BOV need to have the vacumm hose conected to be tested?

Or can you test it seperate from the car ?
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Old 03-08-2013, 07:13 PM   #6
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Lolz, you mean the BOV ?

Out of curiosity I'm out in my garage testing my BOV now.

Does the BOV need to have the vacuum hose connected to be tested?

Or can you test it separate from the car ?
Lolz, I just worked out that under Vacuum the the valve is in the open position all the time and and is only closed when the car is under boost.

Testing continues.......
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Old 03-08-2013, 07:38 PM   #7
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What brand BOV?
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Old 03-08-2013, 07:39 PM   #8
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If you disconnect the vacuum hose from the BOV and drive it, it'll make that same flutter sound, but more pronounced.
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Old 03-08-2013, 08:46 PM   #9
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What brand BOV?
Forge

I just ran the red spring with two shims = no noise, The fluttering noise is gone.

I think I need to set up my BOV properly
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Old 03-09-2013, 08:25 AM   #10
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Be very careful, this is how one screws the pooch in regards to the turbo. When I put a t3 super 60 in my old car, this did the same thing right off the bat. Replaced spring in diverter valve, fixed!

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Old 03-11-2013, 11:07 PM   #11
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Yeah, mine makes the same noises...which is why I posted about it a couple days ago. Thanks for putting a video up...my car has an exhaust note that overwhelms the camera. Mine is louder though. I don't know if this is flutter from the BPV or surge. Same Chtchtchtchtcht rapid flutter kinda sound.
I actually took some shims outta my forge unit as I was getting compressor stall when I let off the gas at lower boost--a hallmark of too-tight a BOV spring.
I am currently designing a system that doesn't rely on goddamned Precambrian technology. I am using a a rotor-barrel valve and a stepper motor and a delta switch hooked up to the TPS...perhaps some logic with an Arduino.
I hate BPV's/BOV's...they all require compromise--balancing spring just-so that it almost doesn't release under low-boost, but holds for high boost, while ensuring it opens fast enough and wide enough to dump everything at high boost and rapidly shut throttle conditions.


So now the question; is it a BPV/BOV issue or is it the outer fringes of compressor surge? If we T28'ers pursue the BOV issue when it is actually surge, then we run the risk of worsening an already precarious situation.
Be nice if these things had compressor maps w/surge lines.
-Cm
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Old 03-24-2013, 08:09 PM   #12
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Yeah, mine makes the same noises...which is why I posted about it a couple days ago. Thanks for putting a video up...my car has an exhaust note that overwhelms the camera. Mine is louder though. I don't know if this is flutter from the BPV or surge. Same Chtchtchtchtcht rapid flutter kinda sound.
I actually took some shims outta my forge unit as I was getting compressor stall when I let off the gas at lower boost--a hallmark of too-tight a BOV spring.
I am currently designing a system that doesn't rely on goddamned Precambrian technology. I am using a a rotor-barrel valve and a stepper motor and a delta switch hooked up to the TPS...perhaps some logic with an Arduino.
I hate BPV's/BOV's...they all require compromise--balancing spring just-so that it almost doesn't release under low-boost, but holds for high boost, while ensuring it opens fast enough and wide enough to dump everything at high boost and rapidly shut throttle conditions.


So now the question; is it a BPV/BOV issue or is it the outer fringes of compressor surge? If we T28'ers pursue the BOV issue when it is actually surge, then we run the risk of worsening an already precarious situation.
Be nice if these things had compressor maps w/surge lines.
-Cm

check out synapse synaptic blow off valve. it works with a vac line and is instant compared to old style its alot better.


it works better at boost levels that differ. if you set your bov for full throttle 50psi and expect it to blow off great for 1psi with a conventional bov your wrong. the pneumatic design is the best ive seen. it will work for any boost level and blow off just as qucik



http://www.youtube.com/watch?feature...&v=k_hlqNbfdmE

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Last edited by pitman; 03-24-2013 at 08:18 PM.
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Old 03-25-2013, 06:42 AM   #13
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Quote:
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check out synapse synaptic blow off valve. it works with a vac line and is instant compared to old style its alot better.
https://www.saablink.net/forum/perfor...-9-3/60792.htm
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Old 03-25-2013, 07:07 AM   #14
 
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That sounds far better than the nasty SSVs.....
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Old 03-25-2013, 07:08 AM   #15
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The video sounds like real comp surge, not the lift off turbo stall noise.
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Old 03-25-2013, 06:45 PM   #16
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Originally Posted by pitman View Post
check out synapse synaptic blow off valve. it works with a vac line and is instant compared to old style its alot better.


it works better at boost levels that differ. if you set your bov for full throttle 50psi and expect it to blow off great for 1psi with a conventional bov your wrong. the pneumatic design is the best ive seen. it will work for any boost level and blow off just as qucik



Synapse Engineering Company Overview 2012 - YouTube

Actuator Based On Synchronic Technology - YouTube
Yeah this is the one I recommended. We had one on a 300 HP miata. The change in throttle response between shifts was very noticeable. I would be seriously considering their dv if it wasnt for the turbo I'm looking at already having one integrated in the compressor housing.
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Old 03-25-2013, 08:26 PM   #17
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awesome. glad to see your still in the saab. do you have a gt30r still or hx35? its been awhile since ive been on here. i need another saab.
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