Zeff

Hey guys is this what 'chirping' sounds like from the dv?

http://zeffy.net/951parts/951dv.mp3

Paulyy

to me it sounds like a flutter as in compressor surge.

AScholtes

yes, compressor surge

Zeff

ok... from reading on here that happens because the DV isn't releasing the boosted air fast enough correct?

If so, I gotta figure out what to check. I was experiencing compressor surge with the stock dv so I replaced it with an aluminum one (ebay comes with several springs). I'm still getting the surge.

Paulyy

have you tried different spring rates? and find any different results?

Zeff

No, not yet, just got the thing installed and went for a drive this afternoon and heard the same thing again. I've got a couple hours before work tomorrow, I'll try to take it apart and use a different one.

Black51

Did you check all vacuum hoses, including the black hose that adapts the DV into the j-boot? Check the j-boot itself? I could really see the vacuum hose that leads to the DV to causing comp surge if there were a leak. The valve wouldn't fully open.

NZ951

I dont think thats compressor surge. I doubt you were generating enough pressure in those runs to outflow your DV. It sounds more like the DV value fluttering, issue is to do with the spring rate in the old bosch. Its not really the end of the world. I tried a few different springs on a 50mm tial valve and got rid of most of it, the sequential HKS ones seem to work, some these days are adjustable so you dont need to shim the spring or change it.

Zeff

When I installed the new DV I didn't see any cracks but I didn't pull the whole jboot off. I had all new vacuum hoses done earlier this year and the car pulls hard. I'm just the only one in the area now with a 951 so I have nothing to compare to.

Zeff

Ok, the recording varied between 10-15 psi, if I do WOT to redline I don't/cant hear any flutter, only when I hit partial boost and change gears.

AScholtes

I can tell you absolute certainty it is compressor surge (actual defined term is axi-symmetric stall). It really doesnt matter how much boost is being made, the surge is caused by rapid changes in air pressure that causes buffeting in the the compressor housing. This is why a bypass (recirculating) valve works. It recirculates the boosted pressure to the inlet side of the compressor to keep the turbine from having a stall condition and causing the surge. if the valve does not actuate quickly enough, you get the surge effect, if it does not flow enough, you get the same effect...what happens is that pressure tries to back flow through the turbine and causes this effect, putting alot of opposing forces on the turbine wheel and shaft...

NZ951

Compressor surge sounds like a turkey gobbling... thats not what Im hearing, I hear a flutter, but could be my hearing

AScholtes

Compressor surge sounds like a rapid whoosh whoosh whoosh sound... but not all sounds the same. Typically when you hear one that sounds like a turkey gobbling (really high pitched) you need to start looking for compressor wheel damage.. anyway, here's a video (sorry, its the best example I could find) of what the most common sound for compressor surge is... listen all the way to the end, and never mind the chipmunks...

http://www.youtube.com/watch?v=udXdXCv1r2Y

AScholtes

PS... Zeff, I just noticed you are in Asheville... right up the road from me...

hot-J

its surge. If it doesnt happen at wot, but at lower load, the spring is too stiff. Check vaccum lines.