Turbo Flutter/slow BOV

Roadrunner · Postby **Roadrunner** » Wed Apr 22, 2020 7:00 pm

Ever since my SE IHI turbo was upgraded to a GT2860RS (about 2000kms ago) I've not had a distinct BOV pshhh, more a fluttering sound, not full turkey gobble though. I've since had an engine rebuild and there's no change to the sound.
Isolation has given me time to look into it and will try to get video of it tomorrow.
Today I disconnected the recirculation hose and it was very noticeable when I let off the throttle instantly the flutter is definitely from the turbo/intake side and then half second to a second later I hear from the BOV side a peehhhhhh of air coming from the BOV. Almost sounds long and slow, not a harsh PSHHT like you'd expect.
Obviously the BOV isn't opening quick enough and air is going backwards out the turbo
This happens at all PSI levels from vac all the way through to 20psi.

After extensive googling the topic, So far I have:

- Lubed the BOV piston (turbosmart Kompact plumb back) with Turbosmarts secret sauce lube = same
- ran the BOV vacuum source from the larger manifold PCV barb for a larger reference line as suggested by turbosmart = same
- swapped in an identical known working bov = same

I'm now a little lost as to why the BOV isn't venting instantly like it used to on the IHI turbo. Turbosmart say the Kompact BOV is suitable "up to 40psi"

Why did this change as soon as the GT2860RS was put on? Is this characteristic of this particular turbo?

bruce · Postby **bruce** » Wed Apr 22, 2020 8:13 pm

Different turbo means different flow of air results in different effect on BOV.
BOV only regulates air on closed throttle. Wastegate regulates max PSI.

Luke · Postby **Luke** » Wed Apr 22, 2020 9:30 pm

No idea, but the Turbosmart BOV on my SE with a 2860RS Turbo just plain sneezes if any boost is present. I'm setup at a max of 16 PSI.
I have the 3/4inch size one as I have the BEGI intake elbow, with the stock size option.
I see you have the FM one which is 1 inch from memory.
No idea if that would make a difference, other than that you should have a unit that can pass more air, so higher boost capable.

Roadrunner · Postby **Roadrunner** » Wed Apr 22, 2020 9:49 pm

Thanks that's good to know Luke. Even on my 13psi track tune it doesn't sneeze at any psi. If you're turbosmart BOV is smaller and works as expected on the same turbo then there is definitely something not right with my setup. But what....

The American · Postby **The American** » Wed Apr 22, 2020 9:59 pm

Is the vacuum line in good shape, no kinks etc?

Nevyn72 · Postby **Nevyn72** » Wed Apr 22, 2020 10:00 pm

The American wrote:Is the vacuum line in good shape, no kinks etc?

My thoughts exactly, sounds like a vacuum leak, or blocked vacuum line......

Nevyn72 · Postby **Nevyn72** » Wed Apr 22, 2020 10:02 pm

Hang on a minute, in the picture above, is the vacuum line for BOV connected to the boost soleniod? :shock:

Roadrunner · Postby **Roadrunner** » Wed Apr 22, 2020 10:34 pm

The American wrote:Is the vacuum line in good shape, no kinks etc?

Tried different larger vacuum line when I hooked it up to the large PCV barb on the manifold and a different hose again when I tried it on the small barb that the charcoal canister normally connects to.

Nevyn72 wrote:Hang on a minute, in the picture above, is the vacuum line for BOV connected to the boost soleniod?

No it runs behind the intake elbow and up to the barb on top of the manifold. Boost solenoid connects to the right hand side of the intake elbow.

Luke · Postby **Luke** » Thu Apr 23, 2020 12:16 pm

Crazy idea, but is the throttle actually fully closing when the accelerator pedal is fully released?
Or maybe is it even rotating a little to far because of a broken stopper or similar?
Only asking as I can see the Inlet manifold has more than likely come off for painting at one stage.

StuwieP · Postby **StuwieP** » Thu Apr 23, 2020 5:55 pm

Luke wrote:Crazy idea, but is the throttle actually fully closing when the accelerator pedal is fully released?

That shouldn't matter should it? As I understand it the BOV is actuated by the pressure differential either side of the valve, as supplied by the vaccuum line? If the throttle isn't closing, then the boost pressue should still have somewhere to go (into the engine) and shouldn't cause the turbo to stall/flutter?

FWIW I also have a turbosmart plumb-back that quite happily releases anywhere up to 18-odd PSI. Also a 2860RS. I don't think it's turbo-related. Most likely at the BOV side of the equation.

Roadrunner · Postby **Roadrunner** » Thu Apr 23, 2020 6:13 pm

Luke wrote:Crazy idea, but is the throttle actually fully closing when the accelerator pedal is fully released?
Or maybe is it even rotating a little to far because of a broken stopper or similar?
Only asking as I can see the Inlet manifold has more than likely come off for painting at one stage.

Checked it out just in case and all looks fine.

Here's 2 videos.

First:
Recirculating back to the intake pre turbo as in the picture in first post. The BOV vacuum/reference line for these videos is hooked up to the PCV port on top of the manifold to rule out too small vacuum line.

Second Video:
Recirculation hose unplugged from BOV. The Mic is under the bonnet on the BOV side and was getting overwhelmed by the volume of engine and road noise. It's harder to hear but you can still hear the tsu tsu tsu which is definitely from the intake side and you can also hear the BOV release air from the right side. Both noises are a lot clearer in person.

On listening to the second video there is no delay in the BOV releasing like I thought there was and just before the end of the vid I let off the throttle in vacuum and it releases air as expected quite clearly.
So the BOV is working instantly i let off the throttle, but still getting chopped air noise out the intake. Obviously when the BOV recirc hose is plumbed in you can't hear the BOV release at all over the turbo flutter. This only changed after changing turbo (brand new) and intake etc.

As my setup is the same as Luke's bar the intake piping and he runs a smaller BOV than me, I can't understand why this isn't working properly.

bruce · Postby **bruce** » Thu Apr 23, 2020 8:29 pm

Must be an essential trip!

Roadrunner · Postby **Roadrunner** » Thu Apr 23, 2020 10:38 pm

bruce wrote:Must be an essential trip!

Grocery shopping is an essential trip.i recorded the drive there and back. Plus im fortunate enough to have a job to go to at least 2 days a week gives me an opportunity to get it out of the shed :roll:

The American · Postby **The American** » Fri Apr 24, 2020 6:36 am

Do your BOV have adjustment for the spring tension?

It certainly sounds like it is working a little better in the second vid, but not opening far enough to bleed off with a convincing “ppppsshhh”.

Roadrunner · Postby **Roadrunner** » Fri Apr 24, 2020 12:01 pm

The American wrote:Do your BOV have adjustment for the spring tension?

It certainly sounds like it is working a little better in the second vid, but not opening far enough to bleed off with a convincing “ppppsshhh”.

It's not adjustable but I'll get a softer spring for it and see what happens. It's the only thing that makes sense. Engine makes normal vacuum, lines are large and clear, piston is lubricated and free moving.
It's not a complicated device and it's sending me insane haha