Modern Performance
For those of you who hear a fluttering noise after installing a blow off valve in your Dodge Neon SRT-4, Caliber SRT-4, Turbo Cobalt, Turbo Neon, etc, read further.
The common perception of a blow off valve noise, is a solid WHOOSHING noise. In most scenarios, that is the case, HOWEVER, there are some important things to consider in the normal operation of a blow off valve.
First, lets give you a full background on a blow off valve. A blow off valve is a vacuum operated device, that seals the pressure piping when the car is in positive boost pressure, and at times of vacuum, opens and releases pressurized air. For those of you who may not know why a blow off valve does this, you have to consider a turbocharger, spinning at tens of thousands of rpm, being driven by the exhaust gases of the motor. When you shift gears, you release the throttle, and the throttle plate closes briefly. When your throttle plate closes briefly, the turbocharger is continuing to spin, and send pressurized air towards the throttle body. If there was no blow off valve to release the pressurized air when the throttle plate closes, then pressurized air would be sent towards the throttle plate, and either damage the throttle plate, OR worse, could damage the turbo by trying to spin the compressor side of the turbo backwards.
So, the blow off valve, is used to protect your turbocharger, and throttle body primarily, and as a side benefit it makes a cool whistling noise.
Now, back to first time turbo owners and how they assume the blow off valve makes a constant whoosh noise. Since the blow off valve is a vacuum operated device, its operation will be dependent on the boost level within the motor. If your motor has 15 psi when the throttle plate is closed, then the blow off valve will release a LOT of air, making a nice solid whoosh noise. If your motor has 2-3 psi when the throttle plate is closed, then the blow off valve wont make much of a noise, and it will actually make a fluttering noise as the blow off valve internal piston moves back and forth, not fully closing or opening.
So im summary, fluttering is very normal and nothing to worry about, AS LONG as the blow off valve functions correctly when your in higher boost levels. NOW if your blow off valve never makes a solid whoosh noise, more than likely you have a damaged vacuum line, or your car has a boost leak, or some other turbo related problem.
