Overhaulin'

what is the hissing soung in a modified car when i shift (change) a gear?

ive just bought a car and dont know what it is. seen and heard it before on other cars but dont know what it is. the sound goes louder as i accelerate and then when i change a gear it sounds as if some gas was coming out of something. does it give any extra power?

Public Comments

1. Probably a dump-valve : ) Just type in dump valve in your search engine then it will explain all you need to know!
2. Yeah the dump valve they sound sooooooo cool!! You can change gear faster and so accelerate quicker using paddles on the steering wheel instead of a gear stick!
3. yup
4. Yep its the Dump valve. Ptcshhhhhh!
5. Its your dump valve and its releases the build up of hot air from your turbo, This doesnt provide any power hikes but does sound awesome and increases the longevity of your turbo.
6. It sounds like your car is turbo charged and is fitted with a turbo pressure regulating valve, commonly known as a dump valve or blow off valve. The way this works is as follows: A normally aspirated car will "suck" air into the inlet manifold to mix with the fuel for combustion. A turbo charged car on the other hand, will use the flow of exhaust gases to spin a turbine which "blows" or forces air in to mix with the fuel. The reason for this is that the more air you can get into the engine then the more fuel you can mix with it, resulting in a more aggressive combustion and thus more engine power (ie; a faster car). However between gear changes that extra air pressure generated by the turbo needs to go somewhere, so a dump valve is fitted to release the air pressure. This is the "Pffttssss" noise you hear when you shift up a gear. It's not a fault so you don't need to worry about it. Besides, it sounds really cool!
7. you probably have some engine problems. check with your mechanic.
8. its either the blow-off valve releasing excess boost pressure when you change gears, or its your passenger pissing themselves with laughter at you having such a large, loud uneccesary cop bait toy in a road car. ALL turbo vehicles have a blow-off valve to vent excess boost pressure but manufacturers route the boost back into the airbox before the turbo as it is quiet. Tools and loosers take this pipe off so the can hear it happening just like the ultra high performance race cars (which, coincidently, dont have to deal with police)
9. Yep - it's a blow-off valve and I think the sound (particularly of the louder ones) is awful! It sounds really cool for the first 10 times and then every time you change gears.... aaaargh! Same deal as super loud exhausts. And no, it won't give you extra power and in fact can detract from the power if it's not properly integrated with your exhaust and chip set. This is also true for those fat exhaust pipes. (You need a thing called back-pressure to make a turbo work at its peak and if you don't get the right amount for the input rates, you lose - not gain)
10. well these people didnt read what you said quite right. as you accelerate that noise you hear is your turbocharger AKA Turbo. when you shift and you hear that "gas" coming out yes it's your dump valve like the others said. it is perfectly normal. i drive a 2002 wrx impreza and it does give you more power. have fun
11. turbo
12. blow off valve
13. This is the sound that a blow off valve makes on turbocharged engines. The way a turbo works is it gets alot of cold air to get very compressed into a small space so that more air can get in the cylinders to produce more power. And when you shift, the remaining air needs to be released so the process can start over again, so the blow off valve releases all the remaining air making that pshhhht noise. The noise itself does not give the car any extra power, but that noise means you have a turbocharger which can create a TON of power. The reason the sound goes louder as you accelerate is because the turbo is spooling up and will only engage at high RPM's right before you shift. Hope this info is helpful. If you want more try going to www.howstuffworks.com and looking up turbochargers.
14. That'll be your dump valve....they are fitted to turbo charged cars...see the links below for a fairly easy understanding of them....you need to get the right type for your car, but I'm assuming because you bought the car with one fitted it's ok, but check anyway, some people put in whats cooler and it mightn't be right, a 'forge' dump valve for your Subaru would be good, anyway check it out either way. :)