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Interesting note on the GFB website:

"Also, large front-mounted intercoolers can increase the likelihood of ‘flutter' for any given BOV, due to the larger volume of air present in the intake system. If the BOV is any good, some adjustment of the spring preload would be all that is necessary to once again eliminate the flutter."

When the factory turbo shat itself I put a larger 500x200mm core x 2.5in thick PWR intercooler on while waiting for the new turbo and bits were installed. Fingers crossed a softer spring will fix this.

Wouldn't a more efficient turbo also increase the volume of air in the intake system?

Lighter Turbosmart spring finally arrived. Still a tiny bit of flutter when jumping off the throttle at high boost but it's 95% better. Will try plumbing the vacuum source with large hose direct to the larger pcv nipple again to see if that cures all but for now that seems to have sorted it. If not I'm going to assume its just a characteristic of the short straight intake pipe off the turbo.

Will you record the sound as well?

I have been meaning to do the exact same thing with my SP - I had a bias spring arrive last week but I'm away for work!

I'm interested if you think it has had any affect on throttle response - particularly when lifting off and coming back on - as the purpose of correctly speccing the BOV bias is to prevent the turbo stalling?

Sure, I’ll do a video again when I get a chance. No effect on throttle response that I’ve noticed.

Roadrunner wrote: plumbing the vacuum source with large hose direct to the larger pcv nipple

Shouldn't the pressure be the same at both ends of the hose regardless of its diameter? The larger hose might cause a delayed reaction as the pressure change would happen ever so slightly more slowly?

The advice from Turbosmart is if you are having issues, one of the first things to do is use a larger hose from a larger manifold barb because larger diameter hose reacts quicker. I'm testing out the larger hose on the way to work today so will see what difference there is. I've been keeping a keen ear on it and from 0-8psi there is no flutter but at higher pressure there is. I get the pssst from the BOV but can also hear a woowoowoo from the air filter as well. So better than before but still not perfect.

So no difference at all with the larger vacuum hose direct from the manifold.
Its significantly better than before with the stronger spring. The valve is dumping hard short pssts the instant I back off so I’m going to assume the noise from the intake is just a byproduct of the large straight intake pipe welded to the turbo which would be like an echo chamber.
I officially give up.

Roadrunner wrote:So no difference at all with the larger vacuum hose direct from the manifold.
Its significantly better than before with the stronger spring. The valve is dumping hard short pssts the instant I back off so I’m going to assume the noise from the intake is just a byproduct of the large straight intake pipe welded to the turbo which would be like an echo chamber.
I officially give up.

Didn't you get a softer spring?

The other thing to try - and this is what I'll be doing when I finally get home - is hook the hose up to the barb closest to the valve as possible. If you look at the brake you'll see they're always hooked up close to the cylinder so that they pull as much vacuum as soon as possible. It could be the volume after the throttle that is causing the delay in activating the BOV.

Yes softer spring is installed which helped a bit. I connected to the PCV valve barb on the manifold but wondered if plumbing into the brake booster right at the rear of the manifold would make a difference (should be the first area to go into vacuum. I had considered tapping a barb on the rear of the flat top as it's only outlet is right after the throttle plate.
After the turbo install, but before the engine rebuild and flat-top was put on, the BPV was hooked up to one of the small rear ports on the SE manifold but still did it. But maybe the small barb/hose size wasn't helping then.

You don't have that on the SE? That is right in front of the first valve - that is what I was going to try.

lambertius wrote:

You don't have that on the SE? That is right in front of the first valve - that is what I was going to try.

Tried this spot yesterday. No difference. Also hooked into the brake booster line right at the rear of the manifold and also no difference. It's perfect up to 5 or so psi but above that it flutters. I contacted Turbosmart and they said a Kompact has plenty enough piston volume flow for 20psi and especially 12psi where it still happens. They suggested with everything I've tried it could just be the all metal free flowing intake and intercooler and short pipe to pod filter is amplifying the noise and that it should be fine. Currently the BPV routes back to the intake box so I'm going to try routing in to the intake pipe itself just before the turbo, if it changes nothing flutter noise wise it may just help a little with spool.

FWIW I've got an SP, and I've dríven two other SPs and we've got super long intake piping, a larger volume intercooler than the SE and a (I think) GT2560R turbo. They all flutter.

I've done as much as I can with mine, hooked up the BOV close to the valve with the softer spring. It did push the flutter further down (as in I need to drive it a bit harder for it to flutter now), it is also not as loud as previously, and the other owners agree that mine is less aggressive on lift off. I think in my case its a combination of the specific turbo and the large intake volume.

Ok that's good to know. I was finding it difficult to understand why I was the only one having this issue. I've got a M12 to 5/16inch barb that I'm going to tap into the rear of the flat top manifold as a dedicated vacuum line for the BOV tomorrow. I'm not expecting any change though

I just had a thought - have you replaced the OEM air box?