Tom M'Guinn

I understand you can damage the turbo blades if the surge is enough to be audible like that, and you must also be losing boost between shifts. A new valve is something line $25. Ok, off the soap box for me.

rage2

Yea, it's very very light surging. Basically have the BOV to open at around 20psi right now. Not enough surging to lose boost on shifts though.

Tom M'Guinn

Ignore me if I am being a pest, but I think we may be on different pages. When I said "blow off valve" I was referring to the bypass valve (aka air recirculation value) that connnects to the intercooler pipe. This valve cannot be set to any pressure (unless you have some funky aftermarket valve?). It looks like a small black canister with one small vacuum hose running to it. When you let off the throttle, the vacuum line pulls the valve open, diverting the compressed air back to the front of the turbo inlet. If the valve does not open, since the turbo is still spinning fast, boost will back up between the turbo and the closed throttle plate. This backed up boost needs someplace to escape, so it beats up the turbo blades and finds its way out via the turkey gobble sound your car is making. These valves go bad all the time, and are cheap and easy to fix. I bet a nickel that your's is not working, and that the sound will go away if you replace it (not to mention better boost on upshift, longer turbo life, fewer vacuum leaks, etc.).

dand86951

Tom, your comments are interesting to me as my car makes the same sound. I have taken the BOV off and tested it per the manual by trying to blow and suck through the various openings and according to that mine is still working correctly. I thought the sound was simply more noticeable because of the MAF being much more open directly to the atmosphere rather than through the stock labrynthian air filter intake system?? Rage has an SDS system and the same short intake track between the K&N and the compressor wheel.

Tom M'Guinn

Keep in mind, I was only willing to wager a nickel on it, based on the video. I have a Huntley MAF (and big turbo), with a K&N filter, making 330rwhp on good days. My car made that sound until I replaced the bypass valve. Once I replaced the valve (with the superseding 993TT part), the noise went away. I made my last post because of the comment about setting the valve to 20psi. That made me think there was some confusion, since the valve cannot be adjusted in any particular way.

Tom M'Guinn

Oh, and you may want to check the vacuum at the hose going to the valve. If that vacuum line is not pulling a good vacuum, the valve won't open and your car will make that sound.

atinybug

here's something interesting... my mechanic has a wrecked j-spec s13 silvia that was set up for drifting, someone brought it over from japan to use for parts. the top and bottom loops for the springs are welded to the 2nd loop to make the spring shorter and not bounce as much.

rage2

hehe car's far from stock . I have an adjustable blow off valve on my car. SDS standalone, MAP sensor. No MAF, so I can use a real blow off valve. The stock recirc valve was tossed out years ago. And yes, the K&N at the edge of the turbo exagerates the sound.

It has to be adjusted high, otherwise it leaks at high boost (anything over 18psi). With this setup I can run 28psi without leakage. And adjusting it is a bitch... not the most user friendly blow off valve.

Like I said, it'll be upgraded to a more easily adjustable blow off valve once I get the 2.8L in there, and my new intake pipes are done.