Dump Valves - Do They Enhance Performance?
11 November 2003, 08:19 PM
#1
Or do they just sound good?
I've never wanted one in PTMW! as although the sound of a Noble M12 popping and dumping 10 inches from your ear is aural orgasm, I don't think it'd do much for me on a daily basis.
My POV obviously but brought home when the Essex Convoy turned up @ Brands & I'd just been chatting to one of the XTR crews.
As the lovely rumble of scoobs (can we coin that as a scoob gathering? "Rumble of Scoobs"?
) came along the back of the stand, they looked up, then with a popping and a dumping of DVs, they laughed & said - "That'll help them get out of the gravel trap!" 
They obviously considered it more of a Max Power addition than a serious performance aid.
Were they right?
I've never wanted one in PTMW! as although the sound of a Noble M12 popping and dumping 10 inches from your ear is aural orgasm, I don't think it'd do much for me on a daily basis.
My POV obviously but brought home when the Essex Convoy turned up @ Brands & I'd just been chatting to one of the XTR crews.
As the lovely rumble of scoobs (can we coin that as a scoob gathering? "Rumble of Scoobs"?
) came along the back of the stand, they looked up, then with a popping and a dumping of DVs, they laughed & said - "That'll help them get out of the gravel trap!" They obviously considered it more of a Max Power addition than a serious performance aid.
Were they right?
11 November 2003, 08:25 PM
#3
Dunno really, But when the vacuum hose broke off my OE dump valve there was a noticable diference in response between gear-changes.
whichs remind me, I need to adjust the spring on my dump valve...anyone know what pressure/vacuum it should start opening?
whichs remind me, I need to adjust the spring on my dump valve...anyone know what pressure/vacuum it should start opening?
11 November 2003, 08:32 PM
#5
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All the things I've read on the subject seem to indicate that the OEM part is about as good as they come performance wise.
The only reason I can see for changing them is if you want the noise from a VTA type rather than a recirc.
I wouldn't go so far as to say they were gay. . . . perhaps just a little camp though
The only reason I can see for changing them is if you want the noise from a VTA type rather than a recirc.
I wouldn't go so far as to say they were gay. . . . perhaps just a little camp though
11 November 2003, 08:38 PM
#6
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I have personally spoken to many tuners almost all of the Cossie variety but they all say the same thing, they do NOWT for performance if anything they make it worse!
and it certainly did on my STi8, so its in the garage, wanna buy it? it even has a volumn control
no really it does!
and it certainly did on my STi8, so its in the garage, wanna buy it? it even has a volumn control
no really it does!
11 November 2003, 08:45 PM
#7
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Dump valves ?
You should count yourself lucky that the standard Scooby one is ok. The VAG (Bosch) one plastic and they break fairly regularly unless you swap for a (sensible - Bailey/Forge) aftermarket one.
Allegedly keeps things on the boil more when changing gears, but not the reason I got mine !
You should count yourself lucky that the standard Scooby one is ok. The VAG (Bosch) one plastic and they break fairly regularly unless you swap for a (sensible - Bailey/Forge) aftermarket one.
Allegedly keeps things on the boil more when changing gears, but not the reason I got mine !
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11 November 2003, 09:01 PM
#8
Errr, My scoob Dump valve IS plastic...And It broke!!
Mind, I have a feeling it was a heavy handed mechanic at the main dealers when it was in for some work not long after I bought it. They bodged-fixed it by using some brake pipe and superglue
My intercooler fins also got bent too...nothing to do with it being used as a tool tray like an other scoob I saw in the workshop [img]images/smilies/mad.gif[/img]
Mind, I have a feeling it was a heavy handed mechanic at the main dealers when it was in for some work not long after I bought it. They bodged-fixed it by using some brake pipe and superglue
My intercooler fins also got bent too...nothing to do with it being used as a tool tray like an other scoob I saw in the workshop [img]images/smilies/mad.gif[/img]
11 November 2003, 09:33 PM
#10
They do nothing for performance
At the time I had no knowledge of it being broke either - ruling out placebo etc etc.[Edited by ALi-B - 11/11/2003 11:59:28 PM]
11 November 2003, 10:55 PM
#11
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Becauase if it was stuck shut, the turbo air has nowhere to go, and back pressure the turbo, which slows / stops it. So, when you put your foot down, the combustion gas has to then get the turbo spinning again, hence the delay.
If it was working ok, you wouldnt notice the hesitation
People are talking about aftermarket atmospheric DV's in this thread.
MB
If it was working ok, you wouldnt notice the hesitation
People are talking about aftermarket atmospheric DV's in this thread.
MB
11 November 2003, 11:42 PM
#13
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Mark, this is not how a centri blower works. When the discharge route is closed, the discharge pressure reaches maximum for the compressor speed and airflow stops, as no air is being moved, no work is being done and the wheel spins down due to friction only, therfore a dump valve that is open too long will actually spin down a turbo quicker.
However as the throttle is closed, the compression in the mass of moving air causes a pressure wave to travel back up the inlet and into the turbo. This reverse flow will impinge on the compressor wheel and can slow it or stall it and even cause the wheel to fail. The dump valve vents this reverse flow and ideally should then snap shut after its gone.
Therfore a dump valve if set right can improve throttle response, but one that just dumps whenever you lift off will reduce it.
However as the throttle is closed, the compression in the mass of moving air causes a pressure wave to travel back up the inlet and into the turbo. This reverse flow will impinge on the compressor wheel and can slow it or stall it and even cause the wheel to fail. The dump valve vents this reverse flow and ideally should then snap shut after its gone.
Therfore a dump valve if set right can improve throttle response, but one that just dumps whenever you lift off will reduce it.
11 November 2003, 11:54 PM
#14
I know what a dump valve does Mark , infact Gary's definition is better!
I was just debating to the people who just dumbly state they do NOTHING for performance
Truth is they do help, as what's said above. And less stress on the compressor wheel, and thus why they are fitted as standard.
[Edited by ALi-B - 11/12/2003 12:05:31 AM]
, infact Gary's definition is better! I was just debating to the people who just dumbly state they do NOTHING for performance
Truth is they do help, as what's said above. And less stress on the compressor wheel, and thus why they are fitted as standard.
[Edited by ALi-B - 11/12/2003 12:05:31 AM]
12 November 2003, 12:13 AM
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I have also heard the standard dv is good enough -look in Jap Performance Mag for the article on the S202 - it has awsome performance and a standard subaru dv
I changed mine to a new turbosmart adjustable re-circ dump valve on the premise that it would decrease turbo lag - however I think it just does a better job of looking shiny - all show and no go?
Atmospheric dump valves sound awsome on the track, but would get on my nerves on the way to work every morning.....
I changed mine to a new turbosmart adjustable re-circ dump valve on the premise that it would decrease turbo lag - however I think it just does a better job of looking shiny - all show and no go?
Atmospheric dump valves sound awsome on the track, but would get on my nerves on the way to work every morning.....
12 November 2003, 11:15 AM
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I have just changed my OEM DV to a GFB Hybrid it is 50% recirc and 50% VTA it is also adjustable either way.
When I fitted it I noticed less turbo lag and quicker throttle response. As to what performance gains I got? well I have no idea it still isn't an STi6 but it is a lot smoother, the VTA whoosh bit is a bit anoying but I can live with it.
When I fitted it I noticed less turbo lag and quicker throttle response. As to what performance gains I got? well I have no idea it still isn't an STi6 but it is a lot smoother, the VTA whoosh bit is a bit anoying but I can live with it.