Skylined
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Registered: 27th Sep 05
Location: Sideways, Surrey
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Exactly what a dump valve (or BOV) does and what causes turbo flutter like this
http://www.youtube.com/watch?v=SF0JO9TfSjw
My mates astra does it and I think it sounds ace 
I have a general idea of what a dump valve does but need someone technical to explain in more detail
But seen this on another site
"The only problem is that this flutter is extremely unhealthy for your turbo. The flutter is caused when the throttle is shut and air caught betweent the free-spinning turbo and the closed throttle (when you have no vent ie blow-off valve).
The consequent back pressure forces the air back through the turbine blades. The more technical term for this is 'cavitation', which places enormous loads on the turbo and can or more than likely WILL lead to premature wear of the turbo bearings and other load-bearing components."
Anyone care to elucidate..... 
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Nic Barnes
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Registered: 5th Apr 04
Location: nowhere near ginger people
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pretty much sums it up above. basically more air than the dump valve can get rid of.
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Skylined
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Registered: 27th Sep 05
Location: Sideways, Surrey
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So whats the problem? bigger dump valve or reduce boost?
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Nic Barnes
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Registered: 5th Apr 04
Location: nowhere near ginger people
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larger dump valve can cure it yeah, or reducing the boost.
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Wrighty
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Registered: 28th Feb 04
Location: Howden
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boost in inlet + shutting TB oviously the boost has nowhere to go except back through the turbo, the sounds made by the blades 'chopping' the boost as it goes back through the turbo
a bov may re-circulate this pressure into the manifold or vent it to the atmosphere
as for it being unhealthy for your turbo, well yes but it depends how big & strong your turbo is really
my ihi vf34 will be able to take some, but i prefer using my hks ssqv bov as it helps faster spool up.
[Edited on 17-02-2009 by Wrighty]
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Ste
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Registered: 5th Mar 03
Location: Taif, Saudi Arabia
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quote:
Originally posted by Skylined
Exactly what a dump valve (or BOV) does
When the turbo is on boost, it is pressurising the inlet sid eof the engine, the turbo spins at many thousand RPM and carries more inertia than the engine. This means that when you back off the throttle, the engine slows, but the turbo is still spinning and trying to force air into the engine. As the throttle is closed, there is no where for the air to go, so it "backs up" and causes the turbo to stall. To stop the turbo stalling, a dump valve is fitted so the air can escape the inlet manifold and lets the turbo keep spinning and therefore making it quicker to get on boost then the throttle is opened next time.
quote:
Originally posted by Skylined
and what causes turbo flutter like this
That should now be self explainatory.
ste
I would rather lose by a mile because i built my own car, than win by an inch because someone else built it for me.
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Nic Barnes
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Registered: 5th Apr 04
Location: nowhere near ginger people
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how can a dump valve help faster spool up? dont understand that?
guessing as it lets all the associated trapped air out?
[Edited on 17-02-2009 by Nic Barnes]
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Mike
Organiser: North West and North Wales
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Registered: 20th May 06
Location: nr. Skipton, North Yorkshire
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quote:
Originally posted by Nic Barnes
how can a dump valve help faster spool up? dont understand that?
guessing as it lets all the associated trapped air out?
[Edited on 17-02-2009 by Nic Barnes]
A dump valve releases all the air that'd normally make the turbo stall, therefore the turbo keeps it's speed better so has less speed to gain again when spooling hence faster spool up
[Edited on 17-02-2009 by Mike B]
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WATSON
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Registered: 16th Jun 05
Location: Fife, Scotland
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I hate the sound of dump valves! Took mine off the clio today and i get a nice chatter now
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Nic Barnes
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Registered: 5th Apr 04
Location: nowhere near ginger people
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quote:
Originally posted by Mike B
quote:
Originally posted by Nic Barnes
how can a dump valve help faster spool up? dont understand that?
guessing as it lets all the associated trapped air out?
[Edited on 17-02-2009 by Nic Barnes]
A dump valve releases all the air that'd normally make the turbo stall, therefore the turbo keeps it's speed better so has less speed to gain again when spooling hence faster spool up
[Edited on 17-02-2009 by Mike B]
yeah, what i meant to ask was whats good about the bov ssq hks 5860 or whatever it is wrighty has.
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Skylined
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Registered: 27th Sep 05
Location: Sideways, Surrey
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Cleared things up thanks 
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Mike
Organiser: North West and North Wales
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Registered: 20th May 06
Location: nr. Skipton, North Yorkshire
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I think it was just the point that he didn't think having no bov would shorten the life of his turbo all that much but he prefers to have the bov because of the faster spool. I'm not sure there's anything particularly special about the HKS ssqv, it just happens to be what he has. The only possible difference I know of is they sound slightly different to a normal dump valve
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