What's this pneumatic sound I'm hearing from cars these days?

There are a couple of cars in my neighbourhood making the sound, and I’ve heard it other places recently, too - on shifting, the car makes a sharp, pneumatic wheezing sound. It almost sounds like the sound a bus makes when it is lowering itself to the ground. Is this a pneumatic shifter of some kind? Is this the latest hotness for kids to do to their little hotrods? I wish I could find a sound file of the sound, but I have been unable to so far.

Wastegate on a turbocharged engine venting back pressure.

Missed EDIT window, I meant Blow Off Valve, not Wastegate.

That’s it exactly! Thanks, industrialfish.

This video is a good example of it.

So, is there a reason for cars to be making these sounds?

Yes. Turbochargers are powered by exhaust gases, and when you shift gears there is a momentary lack of air being sucked in by the engine, but still some exhaust gas spinning the turbo creating pressure against the engine intake. The BOV vents this pressure so that it doesn’t build up to an excess while the engine isn’t using it, preventing blown gaskets etc.

Here’s a good write-up:

Is there a reason I’m hearing particularly loud ones all of a sudden? Have they been on turbo cars all along?

most factory turbo cars vent the blow-off valve back into the intake duct. A common mod that jackwagons do is to vent it to the outside, which causes the “pssssh!” sound that so many dipshits think is impressive.

/disgruntled SRT-4 owner who hates other SRT-4 owners.

I believe it is also possible to obtain devices which will make this noise at the appropriate time without actually being on a turbo car, for those who wish to “impress” but can’t afford the engine to do it for real :).

Or you can build your own.

Sad, really.

I had a feeling there might have been a “dipshit” factor, based on the cars I’ve seen that are making this sound. :slight_smile:

It’s the grown up version of putting a card in your bicycle tire spokes.