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Discussion Starter · #1 ·
With all my new mods, I have developed a fluttering sound at WOT.

I am thinking my Forge came with a 15psi max spring and that is the fluttering sound, that I am exceeding that boost and the flutter is the BPV. By ear, the location is high drivers side front which is the right location.

Only other thing I can think of is the wastegate. Anyone else experience this?

I figure throwing a beefier spring in the Forge is a cheap way of diagnosing.
 

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Discussion Starter · #6 ·
hah... such strong opinions in that thread.
Yeah.

All I know is, with some links that SRP sent of Turbo Cobalt owners running Forge BPVs, they all describe the exact sound and sensation I am getting. They all point to shims as the cure or uprated springs and or shims. So I will try a shim or two first.
 

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Discussion Starter · #7 ·
Turns out I have the green spring which is rated 5-15psi. Cobalt people seem to great results with shimmed green springs holding 22psi with no issues. So off to Home Depot I go!
 

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You're fighting an up-hill battle if you have it installed incorrectly.
do you have it so the pressure from the vacuum hose is pushing the piston against the pressure of the charge-pipe?

(also, you won't need a heavy spring)
 

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Discussion Starter · #10 ·
well?? how'd it go?
I found kind of thin fender washers, put in two, it made the car laggy and I still had flutter.

I went and bought a gold 15-23 psi spring and will give that a try.

I did some boost logs and make a healthy 17.2psi in 2-3rd and 17.8 psi in 4th. It tapers a bit as expected at 6k, its more like 15ish.

You're fighting an up-hill battle if you have it installed incorrectly.
do you have it so the pressure from the vacuum hose is pushing the piston against the pressure of the charge-pipe?

(also, you won't need a heavy spring)
It's installed correctly. Again, I have had 0-issues, this flutter popped up after the added boost of the 18T install.
 

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What's your boost source for the valve?
You're not using the solenoid, are you?

Going straight from the manifold to bpv, I hope!
 

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Discussion Starter · #12 ·
What's your boost source for the valve?
You're not using the solenoid, are you?

Going straight from the manifold to bpv, I hope!
Correct, did the BPV mod a long time ago. I did put a proper cap on the line from the TB yesterday though, it was a bit ghetto rigged previously.
 

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Discussion Starter · #14 ·
New tune is in, 18-19psi, figured the green 15psi spring was not ideal. I put in the yellow 23psi spring.

I still get the flutter. However, I noticed it does not do it at WOT/100%, 50-90% I get the flutter. Wouldn't that point to a small vacuum leak causing the noise?

The only other thing I can thing of, there seems to be a bend/kink in the wastegate rod.
 

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I don't know, Jameson.

I have the base spring in my valve, and it's set up the way I said.

I have the recirc valve pressure line coming off the nipple with the fpr and the line that would come back from the solenoid capped on the throttlebody.

It works flawlessly.
 

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there seems to be a bend/kink in the wastegate rod.
This was done when Dave Kennedy built the turbo, it needs to be bent to work with the 6cm housing. A lot of waste gates utilize "bent" rods.



Never had any issues with fluttering. But also never ran at 18-19psi and very rarely even hit WOT.
 

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Discussion Starter · #19 ·
This was done when Dave Kennedy built the turbo, it needs to be bent to work with the 6cm housing. A lot of waste gates utilize "bent" rods.



Never had any issues with fluttering. But also never ran at 18-19psi and very rarely even hit WOT.
Good to know about the rod otherwise I could have replaced it thinking it was no good lol.
 

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I know Jak Stoll used to talk a lot about waste gates being blown open under too much boost. The c900 guys were using helper springs and such to cure the problem... not sure that would be the issue at only 18-19 PSI?
 
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