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hey guys. alright, so i am running an ard (17psi) green tune with an open air filter in my t5-r. i recently installed a forge cbv with a yellow spring (15-23psi) from viva performance, and i got a weird fluttering sound when i let off of the throttle. Initially i thought it was compressor surge, so I swapped in the stock green spring that comes with the valve. However I still get the sound when I let off of the throttle. The sound comes from the actual intake filter when i rev with an open hood. I've looked through the forums, and some say that the sound is compressor surge while some say that it's perfectly normal, called "wastegate chatter," and that the reason it's easy to hear is because of the open air filter. I've made sure that the cbv is installed properly, with the crescent lining up to the one on the housing, more towards the passenger side, and the nipple for the vac line turned towards the driver side. below i've added a link for the cbv that i have and a link to what sounds pretty identical to what i'm experiencing. Any help would be great.

http://www.vivaperformance.com/cbv-upgrade-piston-style-mitsubishi-td04hl-turbos-fmdvrmr/

http://www.youtube.com/watch?v=UUKtcCvZtVY
 

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It's wastegate chatter, I had the same CBV in my 2.5T S60. My stock R CBV also makes the same chatter noise.

The reason you hear it chattering is because when you let off the gas when boost is at mid pressure (5-10psi) there is only enough force to push the CBV open for a split second before it closes and the force builds back up again enough to open it. This happens multiple times in a split second so you hear this chatter sound, it's just the CBV opening and closing really quickly, it won't damage anything.

Compressor surge is dangerous and sounds completely different to the trained ear. If you had compressor surge you would know something was seriously wrong.
 
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