Why Do Paddleshift Cars Fart When They Shift Up?

"Mikeado" (mikeado)
11/06/2013 at 17:14 • Filed to: None

This video by YouTube supercar hero Marchettino of "you" driving an F-Type V6S reminds me (reapeatedly), that I've heard an increasing number of sporty cars with autos and DCTs make this farting noise when they change gear. For some reason I've decided it's been added in by boffins, but why? Is it mean to sound like a racecar's sequential 'box? Because it sounds more like someone sneezing (from either end) or bringing up phlegm...

EDIT: Some are saying it's the car cutting the fuel delivery or some such like during the gear change. This seems like the right answer, but I'm still suspicious of added effects, especially given the exhaust popping so much on the overrun, which I don't think would actually happen that much in a relatively normal modern engine.

DISCUSSION (15)

EL_ULY > Mikeado
11/06/2013 at 17:18

because you're giving it the beans?

Mikeado > EL_ULY
11/06/2013 at 17:20

OK, but why does that cause farting to occur? Are the fears changing really that loud? I still think it's trickery to make it "feel mechanical" or whatever they want journos to write about it.

hangus77 > Mikeado
11/06/2013 at 17:24

I think that it has something to do with the fact that it cuts the fuel during the upshift, but the throttle is wide open. That might induce some funny/cool noises.

EL_ULY > Mikeado
11/06/2013 at 17:25

i was thinking the same, added mechanical "magic" to make it seem like its not a refined machine.

doodon2whls > Mikeado
11/06/2013 at 17:31

Depending on the engine/trans calibration strategy, it's due to the engine controller cutting the throttle, or retarding spark to reduce the torque output of the engine during gear changes.

Some slushbox equipped cars even have torque reduction during upshifts to extend the life of the clutch packs. This momentary torque reduction results in a burp on upshifts. The Chrysler 6.4L/A580 setup does this pretty noticeably.

Casper > Mikeado
11/06/2013 at 17:32

Are you talking about the hard gear change sound or the pressure relief from the boost system?

CAR_IS_MI > Mikeado
11/06/2013 at 17:36

I actually don't have a knowledgeable response for this other than a change in pressure in the exhaust. As the shifts are so quick, an engine is going from 7,000 rpm to 4,500 rpm in an instant, and this creates a change of pressure in the exhaust. That's the only semi logical thing I can think of.

Mikeado > Casper
11/06/2013 at 17:40

Gear change, not the probably-also-synthetic exhaust popping you can also hear.

Casper > Mikeado
11/06/2013 at 17:42

Are you talking about the "psssshhhh" sound when he shifts up? Sounds like rushing air? I'm pretty sure that's the supercharger pressure relief valve opening.

HammerheadFistpunch > Mikeado
11/06/2013 at 17:58

With the jag, they intentionally program the fuel management to do that for the experience. Same with V8 Vantage, same with lots of cars of this ilk. Its definitely real though.

Mikeado > HammerheadFistpunch
11/06/2013 at 18:57

Ah, I see. Thanks.

All Motor Is Best Motor > Mikeado
11/06/2013 at 19:19

You want farts? Skip to 2:19 in this video.

Biostar01 > Mikeado
11/19/2013 at 18:59

I don't know, but all I know that it is sounds insanely pleasurable.

Especially in the CL/A45AMG.

Gerald Gama > Casper
01/24/2015 at 14:13

Psssshhhh & fart are two different things, listen to a standard golf 7 GTi shift on high revs... That's a fart

Nakes_335 > EL_ULY
12/21/2015 at 21:49

Its just like a normal turbo blow off sound on highly modified cars except this has a fuel cut to an open throttle