What causes this sound?...

[tjw2007]

There's a guy who drives past me like a maniac every morning when I'm on my way to work and everytime he changes gear there's a sound like a loud hydraulic piston, it seems to be when he puts the clutch down. He's obviously 'modded' his car quite a lot and it seems really fast - so was just wondering if anybody might know what causing this sound?

Cheers.

[Izo Azlion]

Its a Blow Off Value, or "Dump" valve.

This occurs as air builds up to be used by the Turbo, and as he changes gear its "blown off" or "dumped."

It can be done much more silently but some of them make a pretty nice sound.

That said, there are lame ass speakers you can get put inside the bonnet, which will make the same sound every time you shift gears.

What car is it, out of curiosity?

[Hansi]

I've allso heard about air supported transmission which might make this sound but I don't even know if that really excists. It is most likely a blow off valve I think

[HDi fun]

air suspension was known on some of the Merecedes Benz S class models. This could make similar noises to those you describe.

[waynne]

I'd be interested to know what sort of car it is. It does sound like a dump valve to me. Only really works on turbos and some modern turbo engines dont appreciate the "lost air pressure."

[tjw2007]

I'm not sure, but I think it's a Subaru Impreza - but it looks like quite an old one. The noise is really loud though, like those hydraulic brakes you get on buses and lorries.

[ascaudio]

definatly a dump valve ona scooby lol

[billyo]

Do you know there is a virus code in your website ascaudio?

I get this message :- The requested object is INFECTED. The following viruses Trojan-Spy.HTML.Fraud.ce were found

Probably means you've been hacked.

[HDi fun]

Lorries and buses generally use air brakes. Cars use hydraulic ones.

[waynne]

(Derailing this thread - sorry!) Are there any benefits to air brakes? I would have thought hydraulic brakes would work better on everything buses included.