[rjd_F30]

Originally Posted by BunkerJ

Flutter is created from boost hitting the blades while it's spinning. Think of a fan turned on and you blowing into it. The DV+ does this when you let off the pedal and the boost tries escape, it's now going through one hole, so some is bound to go back. That's why it's not as loud as your normal flutter, but loud enough to hear while in the car.

gotcha, makes sense. thanks

[ilivas]

That flutter is compressor surge. Not good

[allen841231]

Originally Posted by ilivas

That flutter is compressor surge. Not good

can you elaborate a bit more? thanks in advance

[BunkerJ]

Originally Posted by ilivas

That flutter is compressor surge. Not good

Originally Posted by allen841231

can you elaborate a bit more? thanks in advance

I stand corrected on our issue now that I think about it. In our case, it's highly unlikely that we're getting compressor surge. It's very likely valve flutter that we're getting. If you're getting during WOT or after WOT, then I'd call it compressor surge. This only occurs at low boost in my case, which is causing the valve to bounce. Normal and not harmful

[Solidjake]

OP, THANKS for the steps. No way the 5mm will fit if it's not grinded? Also how is the wastegate removed. Thanks

[lonecitizenfour]

Originally Posted by BunkerJ

I stand corrected on our issue now that I think about it. In our case, it's highly unlikely that we're getting compressor surge. It's very likely valve flutter that we're getting. If you're getting during WOT or after WOT, then I'd call it compressor surge. This only occurs at low boost in my case, which is causing the valve to bounce. Normal and not harmful

Where does the valve flutter come from? That noise sounds exactly like compressor surge... is there another part that is a fan somewhere and has air hitting from the blowing side (i mean even if that's not turbo, it can't be good no?)

Thanks

[1SLO4G]

Originally Posted by Solidjake

OP, THANKS for the steps. No way the 5mm will fit if it's not grinded? Also how is the wastegate removed. Thanks

Your welcome, and yes you need to be girded down the tool because you won't able to fit the tool between the block and DV the clearance is super tight and you need to go in an angle already. The waste gate is held by 2 screws and you won't be removing it you will be moving it up and to the side. Hope that helps.

[rjd_F30]

Originally Posted by lonecitizenfour

Where does the valve flutter come from? That noise sounds exactly like compressor surge... is there another part that is a fan somewhere and has air hitting from the blowing side (i mean even if that's not turbo, it can't be good no?)

Thanks

that's kind of what I was thinking. I know compressor surge is no good, but that's the flutter you hear on supras and the like. if the DV+ causes this, then I'm definitely going to avoid it. but if not, like you asked, where is this flutter coming from? what valve, the diverter valve?

[ilivas]

Originally Posted by allen841231

can you elaborate a bit more? thanks in advance

Compressor surge is when the valve doesn’t open and the air doesn’t escape the bypass valve because the spring is too stiff. This causes the excess air to bounce back and forth between the throttle body and the turbo. This can damage the turbo. Basically the air is banging into the compressor wheel of the turbo, that’s the flutter sound.

[ilivas]

Originally Posted by BunkerJ

I stand corrected on our issue now that I think about it. In our case, it's highly unlikely that we're getting compressor surge. It's very likely valve flutter that we're getting. If you're getting during WOT or after WOT, then I'd call it compressor surge. This only occurs at low boost in my case, which is causing the valve to bounce. Normal and not harmful

That flutter is compressor surge. Since it’s only at low boost, it’s not as bad, but still harmful.

Many high hp turbo cars get low boost compressor surge because the springs are so stiff in their blow off valves because they need to hold 50 psi of boost so during normal driving and low boost the valve will not open.

[BunkerJ]

Originally Posted by rjdnyy224

that's kind of what I was thinking. I know compressor surge is no good, but that's the flutter you hear on supras and the like. if the DV+ causes this, then I'm definitely going to avoid it. but if not, like you asked, where is this flutter coming from? what valve, the diverter valve?

Originally Posted by lonecitizenfour

Where does the valve flutter come from? That noise sounds exactly like compressor surge... is there another part that is a fan somewhere and has air hitting from the blowing side (i mean even if that's not turbo, it can't be good no?)

Thanks

Again, I'll say that this is not compressor surge. This is diverter valve flutter. What happens is when you release off the throttle at let's say 50 to 75% and it flutters, the boost is escaping, but because of the pressure changes and one hole, it flutters as it rapidly changes. This also GFB's intention of how their DV's work in general. When you rebuild the system, in addition to the reduced number of holes, you also put in a stiffer spring. This is to ensure that only enough boost gets out that is needed to PREVENT compressor surge. Their intention of doing this is so that you can retain as much boost as you can without hurting the turbo, which is why you get great throttle response with their DV+.

TLDR: Fluttering at low RPM is perfectly normal with a DV+. This is NOT compressor surge and is simply the stiffer spring allowing only the amount of boost out needed to prevent compressor surge. If you get this at full throttle or full throttle liftoff/high rpm liftoff, then you might want to ensure it was installed correctly.

[BunkerJ]

Originally Posted by ilivas

That flutter is compressor surge. Since it’s only at low boost, it’s not as bad, but still harmful.

Many high hp turbo cars get low boost compressor surge because the springs are so stiff in their blow off valves because they need to hold 50 psi of boost so during normal driving and low boost the valve will not open.

See above post. This is not compressor surge.

[ilivas]

Originally Posted by BunkerJ

See above post. This is not compressor surge.

Agree to disagree.

If the valve is “fluttering”, this means it’s closing and air bounces back to the turbo and then back to the valve again to reopen it. This is a light surge.

If at any point during light throttle the valve opens, closes, opens, during a shift, the air has to go somewhere during the closed period. That’s back into the compressor of the turbo.

[BunkerJ]

Originally Posted by ilivas

Agree to disagree.

If the valve is “fluttering”, this means it’s closing and air bounces back to the turbo and then back to the valve again to reopen it. This is a light surge.

If at any point during light throttle the valve opens, closes, opens, during a shift, the air has to go somewhere during the closed period. That’s back into the compressor of the turbo.

And I disagree to misinformation. Please see the below cited:

"During assembly, you can choose to install the main piston spring (indicated below by the arrow) or not. Using the spring is recommended because it results in the best possible throttle response and minimum lag on gearshift, particularly on manual cars. This can sometimes result in a slightly different sound from the intake at low RPM, which is no cause for alarm – it’s simply the different way in which the valve works. If however the noise is objectionable, removing the spring will make the DV+ operate the same way as the factory valve, albeit at the expense of throttle response.

To explain further, minimum lag on gearshift on any petrol turbo engine is achieved when the diverter or blow-off valve vents only just enough air to prevent compressor surge. Venting more air than necessary increases lag on gearshift because the intercooler is completely relieved of pressure, meaning it takes longer to return to peak boost when the throttle is re-opened.

This is the basis behind GFB’s TMS principle (as explained in this article here), and is also the principle that all GFB valves operate on. The DV+ is no exception, because unlike the factory diverter, the DV+ opens and closes in response to both the ECU command AND the amount of boost pressure in the intercooler. So when the ECU triggers the solenoid, the DV+ piston will only open as far as the boost pressure in the intercooler can push it against the spring. The factory diverter on the other hand will simply open regardless of the boost pressure. The different sound you may hear on throttle lift-off at low RPM is simply because of this different operation method, and it does not adversely affect the turbo or engine.

Removing the spring means the DV+ piston will simply open and close when directed by the ECU, just as the factory diverter does. Rest assured that even with the spring removed, the DV+ will still continue to hold boost normally, however you will forfeit the benefit of the TMS principle and throttle response will be the same as with the factory diverter."

[lonecitizenfour]

So I understand it as the stronger spring in the upgraded diverter valve DOES cause surge at lower boost levels because it's stronger. But being stronger obviously can handle higher boost levels much better than the stock one. This seems like one of those "stock is a compromise of both X and Y application; this one is really good at Y application, but not good as stock on X"

[BunkerJ]

Originally Posted by lonecitizenfour

So I understand it as the stronger spring in the upgraded diverter valve DOES cause surge at lower boost levels because it's stronger. But being stronger obviously can handle higher boost levels much better than the stock one. This seems like one of those "stock is a compromise of both X and Y application; this one is really good at Y application, but not good as stock on X"

Again, this is not compressor surge. This is the valve venting as little as possible. DV+ does not compromise with anything unless you are simply turned off by the flutter at low RPM. At that point, don't buy the DV+ because then it's essentially like the stock one.

[rjd_F30]

I think I'm with BunkerJ on this one. after some reading, I understand the flutter is caused by the valve, which vents less boost at low rpm than the stock DV because the stock DV vents too much, thus allowing the DV+ to help hold boost. compressor surge would happen when not enough boost gets vented and bounces back against the compressor. if I'm misunderstood, please let me know, but I'm pretty sure that's how it works here.

[BunkerJ]

Originally Posted by rjdnyy224

I think I'm with BunkerJ on this one. after some reading, I understand the flutter is caused by the valve, which vents less boost at low rpm than the stock DV because the stock DV vents too much, thus allowing the DV+ to help hold boost. compressor surge would happen when not enough boost gets vented and bounces back against the compressor. if I'm misunderstood, please let me know, but I'm pretty sure that's how it works here.

No, you are correct. While I understand what ilivas is trying to assert about when the valve is closed; however, we're talking about thousandths of seconds that this valve is open and closed. If the valve closed/opened at a much, much slower rate, then I would agree with him. This is not the case. Literally just imagine you taking your finger to an air compressor hose (something that wouldn't hurt, so low PSI) and rapidly covering the tip over and over. While we obviously can't match the speed of the valve, the pressure during the time of the valve closure does not overpower that of the flow outwards, especially in that short of time. Same principle applies to the DV+.

[ilivas]

Originally Posted by BunkerJ

And I disagree to misinformation. Please see the below cited:

"During assembly, you can choose to install the main piston spring (indicated below by the arrow) or not. Using the spring is recommended because it results in the best possible throttle response and minimum lag on gearshift, particularly on manual cars. This can sometimes result in a slightly different sound from the intake at low RPM, which is no cause for alarm – it’s simply the different way in which the valve works. If however the noise is objectionable, removing the spring will make the DV+ operate the same way as the factory valve, albeit at the expense of throttle response.

To explain further, minimum lag on gearshift on any petrol turbo engine is achieved when the diverter or blow-off valve vents only just enough air to prevent compressor surge. Venting more air than necessary increases lag on gearshift because the intercooler is completely relieved of pressure, meaning it takes longer to return to peak boost when the throttle is re-opened.

This is the basis behind GFB’s TMS principle (as explained in this article here), and is also the principle that all GFB valves operate on. The DV+ is no exception, because unlike the factory diverter, the DV+ opens and closes in response to both the ECU command AND the amount of boost pressure in the intercooler. So when the ECU triggers the solenoid, the DV+ piston will only open as far as the boost pressure in the intercooler can push it against the spring. The factory diverter on the other hand will simply open regardless of the boost pressure. The different sound you may hear on throttle lift-off at low RPM is simply because of this different operation method, and it does not adversely affect the turbo or engine.

Removing the spring means the DV+ piston will simply open and close when directed by the ECU, just as the factory diverter does. Rest assured that even with the spring removed, the DV+ will still continue to hold boost normally, however you will forfeit the benefit of the TMS principle and throttle response will be the same as with the factory diverter."

It doesn’t release ALL the excess pressure is what you’re saying. The pressure that is not released is still bounced back to the compressor. This is still a mild form of compressor surge. It’s not full on compressor surge, but some of the air still bouncing back to the turbo.

Some companies for turbo cars make multi piston designs to help mitigate this. I ran a tial single piston on my 700whp sti. It held boost but would get light surge, it does shorten the life of the turbo a bit, but not enough to where I would care since at that power level, things break a lot anyways on a 4 cylinder. In the grand scheme, GFB isn’t a super high end bpv, so I wouldn’t expect a lot out of it. People don’t use those at high power levels.

[ilivas]

Originally Posted by lonecitizenfour

So I understand it as the stronger spring in the upgraded diverter valve DOES cause surge at lower boost levels because it's stronger. But being stronger obviously can handle higher boost levels much better than the stock one. This seems like one of those "stock is a compromise of both X and Y application; this one is really good at Y application, but not good as stock on X"

This is correct, you’re not going to kill your turbo in 10k miles with light surge, but it does shorten the life of the turbo a bit.

[lonecitizenfour]

Originally Posted by BunkerJ

Again, this is not compressor surge. This is the valve venting as little as possible. DV+ does not compromise with anything unless you are simply turned off by the flutter at low RPM. At that point, don't buy the DV+ because then it's essentially like the stock one.

Ah okay. Understood. I might have a misunderstanding of what compressor surge is then.

Off topic... do you think it'd be possible to install this with long ball end screw drivers, patience, with just the intake and charge pipe off? I have a 428i xdrive n26 ewg... thanks.

[ilivas]

Originally Posted by rjdnyy224

I think I'm with BunkerJ on this one. after some reading, I understand the flutter is caused by the valve, which vents less boost at low rpm than the stock DV because the stock DV vents too much, thus allowing the DV+ to help hold boost. compressor surge would happen when not enough boost gets vented and bounces back against the compressor. if I'm misunderstood, please let me know, but I'm pretty sure that's how it works here.

There are varying degrees of compressor surge. Full on compressor surge happens when the valve is stuck shut or you don’t have a bypass valve or blow off valve at all.