a woosh and a shift and the land that we...wait your car is making that noise...?
September 8, 2012 6:45 PM   Subscribe

i hear cars coming up my road, and when they obviously shift to the next gear, i hear a "whoosh" of "air" or something else. what is that?

my '01 civic is a 5 speed, but it never whooshes when i shift. is this some high performance kind of thing? i've caught sight of the cars and they range from VW's to Acuras and beyond. just curious to know what the "whoosh" is.
posted by ps_im_awesome to Technology (7 answers total)
posted by rockindata at 6:48 PM on September 8, 2012

Sounds like a turbocharger, possibly. YouTube has a bunch of videos demonstrating the sound so I'd check that out.
posted by selfnoise at 6:49 PM on September 8, 2012

Specifically, the blowoff valve of the turbo, which may be tuned for performance.

But, the fact that you're hearing this for different cars leads me to believe that you're hearing some kind of audible illusion or echo from the street, and it's coming from a specific spot where cars are downshifting or up shifting to gain or lose speed. As in, the cars have just come around a corner that naturally encourages drivers to shift, and they're stepping on the gas to gain speed on a straight.

So, you're hearing an echo, not living among a bunch of street racers or something.
posted by Cool Papa Bell at 6:58 PM on September 8, 2012

after a little youtube search as directed, I came up with this which is the closest sound to what i've been hearing. i suppose it is the blowoff valve. also, cool papa, i actually live on the start of a one way 3 lane street that happens to be an honest and straight 1/4 mile. so...yeah, i think they flock to my road for just that reason.
posted by ps_im_awesome at 7:08 PM on September 8, 2012

Say hi to Vin Diesel for us. :-)
posted by Cool Papa Bell at 7:48 PM on September 8, 2012

Sounds like a turbocharger, possibly. YouTube has a bunch of videos demonstrating the sound so I'd check that out.

I think a lot of people add some version of this to their non-turbocharged cars. I've heard it coming from cars as diverse as Ladas and Hondas, clearly not turbocharged, and yet they manage that same "pssss-oooo" sound.

And indeed, a google search for "fake turbo dump valve" shows that there is a large market of people who want to make it sound like they have an expensive turbocharger on their engine without actually paying for a turbo.
posted by Forktine at 10:29 PM on September 8, 2012 [1 favorite]

It's definitely a blow-off valve. My previous car had one installed by the previous owner. They're typically a horrible idea for performance as they open the loop and can REALLY screw with your car's O2 sensor. But they scare the ever living shit out of people, if that's your thing. (It wasn't my thing, so I ported mine back into the exhaust.)

Definitely that. Or as Forktine says, some fake version of one.

To clarify: a turbocharger alone will not do this on its own. A turbo is part of a closed-loop system, and no car that I'm aware of comes with a BOV stock. I drive a twin-turbo'ed 335i now that never makes anything close to this noise. (Ze Germans have basically reduced any spin up noise or turbo lag to nil as well.)

Turbos DO spin up and you will occasionally hear that IN the car, but turbos only boost under pressure, and it's a very high pitched an subtle whir as they spool up, and even then, it ain't this.
posted by disillusioned at 3:34 AM on September 9, 2012

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