General Please help me fix my compressor surge!

[silentsnow31802]

Im getting pretty bad compressor surge when trying to accelerate gently onto the highway. It makes the car quite hard to drive around normally.
This does not happen when at WOT or when im accelerating aggressively.
I think I can still hear it surging when cruising down the highway at 70 in 5th but its hard to tell if im imagining it or not because the car is generally pretty loud.

Does anyone have any tips on what to look at?
Im trying to not throw money at it trying to guess.
My initial thought was maybe some adjustable cam gears to try and get the valves to open a little sooner but im not sure if that will help since its happening when slowly accelerating.

 

[Justin DuBois]

A video would help to identify what you are hearing/feeling.
How do you have your Tial Q 50mm BOV configured? Picture of the engine bay please.
Surge is typically heard and felt when the BOV fails to open smoothly, and the intake pressure exceeds what is going into the engine, and forces its way backwards through the turbo compressor. (chew chew chew)

 

[silentsnow31802]

I will get a video ASAP. Wont be home until tonight.

It has a -11psi plain spring. I changed it to this to match my idle vacuum reading and to keep the BOV closed at idle. I will need to check the routing when I get home as well as get a current engine bay picture.

There is indeed a chew chew chew sound. Even when normally shifting the BOV doesnt "woosh" air it "chew chew chew's" out. Any time it opens even after WOT.

 

[Justin DuBois]

I will get a video ASAP. Wont be home until tonight.

It has a -11psi plain spring. I changed it to this to match my idle vacuum reading and to keep the BOV closed at idle. I will need to check the routing when I get home as well as get a current engine bay picture.

There is indeed a chew chew chew sound. Even when normally shifting the BOV doesnt "woosh" air it "chew chew chew's" out. Any time it opens even after WOT.

With this BOV, are you running speed density? It looks like you have a 1G MAF in the pics in your build thread.

 

[silentsnow31802]

Yes I am now on speed density.
Guess I haven't taken pictures for a while....

Added a log of the surge happening. Not sure if that helps anything but I had the file already saved.

 

[Justin DuBois]

Yes I am now on speed density.
Guess I haven't taken pictures for a while....

If you can add something with your current setup that will help.
How much boost are you seeing at part throttle? What kind of boost control are you using?

 

[Justin DuBois]

Log looks like 8psi at part throttle - and where do you have the upper port on the BOV plumbed to? 11 psi spring?
Maybe go back to the 6 psi spring.

 

[silentsnow31802]

Ill take some pictures when I get home.
Im using the Ingersoll rand solenoid controlled by dsmlink.
Ill have to look later what I have the BOV plumbed to. I redid the hoses recently trying to get a cleaner signal to everything.
Ive gone back and forth with the springs and it doesnt seem to make any difference. Deiced to keep the -11psi in so that the BOV stays closed at idle.
The log takes PSI from the intake manifold. Im not sure what the charge pipe between the throttle body and turbo is at.

 

[Justin DuBois]

You might want to ask - Is there pressure in the charge pipe at idle? There shouldn't be any. I think you may want to look at your boost control.

 

[silentsnow31802]

You might want to ask - Is there pressure in the charge pipe at idle? There shouldn't be any. I think you may want to look at your boost control.

I dont think there is. My boost gauge shows 0 at idle. Its plumbed into one of the ports on top of the throttle body that I think is on the boost pipe side.

 

[Justin DuBois]

I dont think there is. My boost gauge shows 0 at idle. Its plumbed into one of the ports on top of the throttle body that I think is on the boost pipe side.

0 boost at idle is 14.7 psi above vacuum in the intake manifold, so there is a differential, and this is what I think is lifting the 6-psi spring BOV open. As soon as you crack the throttle, the differential should go away, the the BOV should close. A lack of differential will keep the BOV closed until the pressure on the face of the valve exceeds the pressure of the spring. IMO, your BOV should leak at idle, or any time you close the throttle. Holding it closed with an 11psi spring, means at least some of that 11psi pressure is going back towards the turbo compressor.

 

[curt-s]

A 11psi spring for a Q is good for -20 to -21 inHg vac (about .75bar). I used to run the same for my BV50 before my cams. Off throttle it opened wide and clear just fine, as it should.

Is this a vac/boost gauge or just positive pressure?

We definitely should have video and a picture of the bay with indication how the BOV is hooked up

 

[DSMPT]

Deiced to keep the -11psi in so that the BOV stays closed at idle.

I think there is a misunderstanding. The BOV spring pressure rate is to control the opening event of BOV, not to control to close by against the boost pressure. You are applying the same amount of boost pressure as in the intake manifold to the BOV while boosting, so it shouldn't open. If you have the surge only when go partial throttle but doesn't happen when WOT, then you may have too stiff spring in the BOV. Try replace the spring with lower rate spring and make sure you take the vacuum/boost source for the BOV from intake manifold. Not from the throttle body ports. Some throttle body port doesn't have sufficient stable vacuum for the BOV.

 

[pauleyman]

Either you have a boost only gauge or it's hooked up incorrectly.
Here is tials chart for bov.
Show us the gauge and where it's hooked up.
Notice tial doesn't ask how much boost you're running.

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[silentsnow31802]

Yes that is the chart I went by when I ordered the spring.
The spring is there to hold it closed during vacuum.
The boost gauge does show negative in/hg but is hooked to (I think) the P port of the throttle body at the moment so it shows the pressure on the piping side of the throttle body, not the intake side.
I did this to keep the T's in the vacuum system to a minimum while I was troubleshooting things.

I get home in about 4 hours. Ill take some pictures then.

 

[pauleyman]

Yes that is the chart I went by when I ordered the spring.
The spring is there to hold it closed during vacuum.
The boost gauge does show negative in/hg but is hooked to (I think) the P port of the throttle body at the moment so it shows the pressure on the piping side of the throttle body, not the intake side.
I did this to keep the T's in the vacuum system to a minimum while I was troubleshooting things.

I get home in about 4 hours. Ill take some pictures then.

Move the boost gauge tap to intake manifold. See what vacuum is. Choose spring accordingly. I think you could have the wrong spring. I assume you have the BOV hooked directly to the intake manifold?

 

[Justin DuBois]

Thank you for the charts and details, that explains a lot about this design. Now thinking you should confirm the hose is going to a port on the intake manifold - not the throttle body, as @DSMPT mentioned.

 

[curt-s]

Yes that is the chart I went by when I ordered the spring.
The spring is there to hold it closed during vacuum.
The boost gauge does show negative in/hg but is hooked to (I think) the P port of the throttle body at the moment so it shows the pressure on the piping side of the throttle body, not the intake side.
I did this to keep the T's in the vacuum system to a minimum while I was troubleshooting things.

I get home in about 4 hours. Ill take some pictures then.

The P port is the correct source for a vac/boost gauge. As stated, for your BOV, you want an unteed line directly from the manifold. Using a TB port really doesn't give you the airflow needed to actuate the BOV fast enough or affect the pressure in its hat fast enough on changes, and can cause delayed opening or chattering issues. This is especially true for a big BOV like a 50mm Q.

Given your airflow, there's no way you're surging a 16g at that RPM. You're just not producing enough to outflow what the engine can injest at 7-8psi and 4k rpm.
I'd sooner say you're having difficulty keeping your BOV shut.

 

[silentsnow31802]

So I went and had a look at my vacuum routing. Sorry if the pictures kind suck. It's dark out.

The gauge is in the P port on the throttle body. This is only for a boost display. The car does not use this to run anything.

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The BOV is a direct line to the intake manifold on the passenger side port facing the front of the car.

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The fuel regulator and MAP sensor are on the intake manifold driver side port.

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The boost controller is plumbed to the turbo J pipe.
Left side is the J Pipe and right side is the wastegate.

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[Justin DuBois]

The plumbing choices look normal.
Is your BOV the Q version? How many ports are on the Q?

 

[silentsnow31802]

I believe it is the Q version.
There is only 1 port.

 

[curt-s]

Have you done a BLT at the turbo to see if the BOV opens at various pressures and to validate your lines are free of splits

 

[silentsnow31802]

I just replaced all of the lines with new hoses so I would hope they're not leaking.
What am BLT?

EDIT: Boost leak test? I have done this up to 30psi at the turbo inlet and everything held.
How would I do this to make sure the BOV is opening?

Wonder if I could safely strap a gopro under the engine bay to watch the blow off valve while driving around, without melting the camera...

 

[Justin DuBois]

A camera under the hood would certainly help determine if the BOV is making the choo choo sound, or if its the compressor.

 

[curt-s]

You'd only be taking video for a short period, it should last. Just don't fix it to the exhaust manifold or something silly like that.
Can we see the whole log or, at least, a larger portion of it including the hard accel area where you say it doesn't happen? I stand by my call that there is a complete lack of ability to surge a 16g at 8psi with a 30% open throttle plate and 4000rpm.