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Compressor surge?

Posted: Feb 12, 2007 10:51 PM
by turbodan
Perhaps I havent notcied it until now, but when throttling back during light accel or when shifting I consistently get this soft fluttering sound. The best way I can describe it is "fthththththth". Its hardly noticeable most of the time. If I'm on it and I upshift quickly, it becomes harsher. If I completely drop the throttle between shifts, its almost a shriek. I do have a Bosch bypass valve installed, and its working correctly. The noise almost sounds like a peice of rubber flapping, like I've got a loose coupler and its farting a little bit. But if I get under the hood, rev it and quickly close the throttle the sound seems to come from the compressor inlet. Its almost a bark if I rev it hard enough before I clam the throttle shut. The BPV is bypassing at the same time, quite a lot actually, but the sound still persists. Am I barking up the wrong tree or does that sound like surge? Maybe I need an additional bypass valve? It runs hard under WOT, no problems until I throttle back. Around town its fine until I lift the throttle to shift, then I hear the flutter.

Posted: Feb 13, 2007 6:27 AM
by Boru
Sounds like your bypass valve... known for a long time in Saab circles as a "hooter" valve because of the noise it would make.
Which Bosch valve are you using?

Posted: Feb 13, 2007 10:38 AM
by turbodan
I think it was from a Ford 2.3 turbo car, but I'm not sure. It would be nice if thats all the sound is. I can live with that. I was just worried it wasn't working correctly and I was toasting my turbo. I'd hate to ruin those sweet, sweet ball bearings.

Posted: Feb 13, 2007 9:36 PM
by Skeen
Sounds pretty normal to me. :dunno:

Posted: Feb 13, 2007 9:42 PM
by turbodan
Cool. I'll get used to it.