Dump valve on MY01 worth it?
29 January 2002, 12:32 PM
#1
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Thinking of getting an Atmo dump valve fitted to my WRX MY01 next week by those nice chappies at TSL. Anyone have one fitted? What differences will I notice?
Cheers,
mark.
Cheers,
mark.
29 January 2002, 12:54 PM
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OK bear with me - Im a noob. AFAIK a dump walve is a device located near the wastegate to hold the boost pressure of the turbo up at high revs so that when you change gear you lose less pressure. If this is true how can it not improve performance or have I totally got the wrong end of the stick.
Is it also true that some turbo models (im interested specifically in the P1) have dump valves which are somewhat subdued by silencers which can be removed to get the full sound effects? Do dump valves usually tend to make any difference to insurance? And last but not least - is a blow off valve the same as a dump valve?
Is it also true that some turbo models (im interested specifically in the P1) have dump valves which are somewhat subdued by silencers which can be removed to get the full sound effects? Do dump valves usually tend to make any difference to insurance? And last but not least - is a blow off valve the same as a dump valve?
29 January 2002, 02:24 PM
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Ok, A dump valve does basically what you have said there P1fan.. It may make your turbo-lagg less noticable, but I wouldnt say it was a Performance upgrade.. Certain Dump valves can hold more pressure than say the standard Recirc Valve, so upgrading to one might have a benafit if you run higher boost..
There have been lots a threads on the pro's and con's of dump valves.. Most turbo cars have recirculation valves as standard.. These valves don't vent to atmoshphere so they don't make the pfffffshhhttt noise!
A BOV or Blow Off Valve is the more suitible name for a Dump Valve, as it Blows off and makes that noise!
I have a SQV HKS Dump valve on my Evo 6, I notice no performance increse wot so ever, but does it make a ferkin loud noise or wot! This is what I bough the valve for, nothing more..
If you want a noticable Performance upgrade and still get that whoooosh noise, then I would suggest getting a Induction Kit of some sort, like a HKS or Blitz kit, as these make nice noises as the car sucks in the air, and they allow the stock recirc valve to be heard better...
There have been lots a threads on the pro's and con's of dump valves.. Most turbo cars have recirculation valves as standard.. These valves don't vent to atmoshphere so they don't make the pfffffshhhttt noise!
A BOV or Blow Off Valve is the more suitible name for a Dump Valve, as it Blows off and makes that noise!
I have a SQV HKS Dump valve on my Evo 6, I notice no performance increse wot so ever, but does it make a ferkin loud noise or wot!
This is what I bough the valve for, nothing more..If you want a noticable Performance upgrade and still get that whoooosh noise, then I would suggest getting a Induction Kit of some sort, like a HKS or Blitz kit, as these make nice noises as the car sucks in the air, and they allow the stock recirc valve to be heard better...
29 January 2002, 02:35 PM
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Dump valves on a Cossie(aftermarket ones)just make that loud pttsssssss noise,which i am now fed up with,so i now use no valve at all,now it sounds like pidgeons have taken over!But it does hold boost better,and just seems quicker!
Can you run a Scooby without one at all??????
Can you run a Scooby without one at all??????
29 January 2002, 02:48 PM
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Hmmmmm!
Where is search when you need it.
First of all a dump valve is already fitted to all scooby turbo's, its a recirculating dump valve which dumps turbo pressure back into the intake system. Pressure is relased through the air filter housing and is silenced by this and the intake resonator. Fitting an induction kit will let you hear more of the standard dump valve but thats another story.
The dump valve is not a performance part it is there to protect the turbo from high stress levels when the throttle is closed, in theory when you close the throttle the turbo is still boosting and would stall. The DV releases this preasure to protect the turbo, when you come back on power the whole intake system has to be re-pressurised by the turbo, so you could say a DV increases lag.
Most high spec turbo engines and WRC's dont use DV's and have high specced turbos with 360 degree thrust bearings to take the stress, DV's are not compatable with anti-lag.
You need to be carefull when fitting an atmo DV to a Scoob as the recirculated air is measured by the MAFM and the fuel adjusted accordingly. You will encounter fueling problems if the atmo DV is not set up right. Most atmo DV's for the scoob hold on to enough pressure to not to confuse the MAFM too much without damaging the Turbo. Not a lot to gain other than the phhhsstttt really.
On a final note if I was to trust anyone to fit an atmo DV it would be TSL.
Cheers
Lee
Where is search when you need it.
First of all a dump valve is already fitted to all scooby turbo's, its a recirculating dump valve which dumps turbo pressure back into the intake system. Pressure is relased through the air filter housing and is silenced by this and the intake resonator. Fitting an induction kit will let you hear more of the standard dump valve but thats another story.
The dump valve is not a performance part it is there to protect the turbo from high stress levels when the throttle is closed, in theory when you close the throttle the turbo is still boosting and would stall. The DV releases this preasure to protect the turbo, when you come back on power the whole intake system has to be re-pressurised by the turbo, so you could say a DV increases lag.
Most high spec turbo engines and WRC's dont use DV's and have high specced turbos with 360 degree thrust bearings to take the stress, DV's are not compatable with anti-lag.
You need to be carefull when fitting an atmo DV to a Scoob as the recirculated air is measured by the MAFM and the fuel adjusted accordingly. You will encounter fueling problems if the atmo DV is not set up right. Most atmo DV's for the scoob hold on to enough pressure to not to confuse the MAFM too much without damaging the Turbo. Not a lot to gain other than the phhhsstttt really.
On a final note if I was to trust anyone to fit an atmo DV it would be TSL.
Cheers
Lee
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29 January 2002, 04:40 PM
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Toerag
I don't think removing the recirc hose is a good idea at all. Not sure what result you'd get if you did that but the stock recirc valve wasn't designed to vent to atmos. I'm sure someone's tried it tho...
In brief, the stock DV comprises of a small sprung piston inside a chamber. It's natural state is to be 'closed'. When you shut the throttle the turbo is forcing air into a closed chamber, at which point the sudden increase in pressure forces the DV piston open and provides a vent for the excess air.
Aftermarket DV's can help when you're running higher boost as the stock DV will sometimes leak a little under these circumstances. I seem to remember hearing of 'safe' DV's which give the pttssshhhh noise whilst still recirculating some of the vented pressure, although I can't recall where these were available.
Whip
I don't think removing the recirc hose is a good idea at all. Not sure what result you'd get if you did that but the stock recirc valve wasn't designed to vent to atmos. I'm sure someone's tried it tho...
In brief, the stock DV comprises of a small sprung piston inside a chamber. It's natural state is to be 'closed'. When you shut the throttle the turbo is forcing air into a closed chamber, at which point the sudden increase in pressure forces the DV piston open and provides a vent for the excess air.
Aftermarket DV's can help when you're running higher boost as the stock DV will sometimes leak a little under these circumstances. I seem to remember hearing of 'safe' DV's which give the pttssshhhh noise whilst still recirculating some of the vented pressure, although I can't recall where these were available.
Whip
29 January 2002, 04:58 PM
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Whip,
Actually, I thought it was the vacuum in the manifold (after closing the throttle) that forces the dumpvalve to open ? Hence the pipe from the manifold to the dumpvalve. Could be wrong though...
Theo
Actually, I thought it was the vacuum in the manifold (after closing the throttle) that forces the dumpvalve to open ? Hence the pipe from the manifold to the dumpvalve. Could be wrong though...
Theo
29 January 2002, 05:36 PM
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The piston face on the stock DV faces the intercooler, so it's logical to assume that the most effective way to operate a piston is by pressure against the face, rather than vacuum from the sprung side. The DV is mainly there to protect the turbo from taking pressure in the opposite direction (this is where 360 degree bearings come in) so it makes sense that the DV is open/closed when boost rises above a certain point (ie turbo still spinning and throttle is shut). Having said that I'm not certain why one of the pipes runs to the manifold, as the recirc path is back to the air intake before the turbo.
This is just how I understand it from my limited knowledge though m8, and I'm happy to be corrected if I'm mistaken
Whip
This is just how I understand it from my limited knowledge though m8, and I'm happy to be corrected if I'm mistaken
Whip
29 January 2002, 05:44 PM
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I whish I would pay more attention when people explain me this stuff 
But
OK, now say you lift off ... pressure before the throttle butterfly (yes I know that's the incorrect name ) builds up even more, pressure in manifold becomes negative.
If it just reacted to pressure, it would never blow off.
Hah
Theo
But
OK, now say you lift off ... pressure before the throttle butterfly (yes I know that's the incorrect name
) builds up even more, pressure in manifold becomes negative.If it just reacted to pressure, it would never blow off.
Hah
Theo
29 January 2002, 05:52 PM
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Not sure I follow your logic there m8.
This bit I don't understand - are you agreeing with me or disagreeing!!
Otherwise your explanation sounds right in that you have the turbo forcing air in at one side, while the other side (throttle butterfly) is now pretty much shut. There have been many cases of DV's 'leaking' (this causes the infamous bottle-top noise) under normal driving on an open throttle. That wouldn't happen if it was manifold-vacuum dependent, it happens because the spring mech in the DV is weakened/defective and isn't holding the piston shut when it should be. At a certain pressure level the DV is supposed to open, full stop.
All of course
Whip
[Edited by whip - 1/29/2002 5:56:39 PM]
If it just reacted to pressure, it would never blow off.
Otherwise your explanation sounds right in that you have the turbo forcing air in at one side, while the other side (throttle butterfly) is now pretty much shut. There have been many cases of DV's 'leaking' (this causes the infamous bottle-top noise) under normal driving on an open throttle. That wouldn't happen if it was manifold-vacuum dependent, it happens because the spring mech in the DV is weakened/defective and isn't holding the piston shut when it should be. At a certain pressure level the DV is supposed to open, full stop.
All
of courseWhip
[Edited by whip - 1/29/2002 5:56:39 PM]
29 January 2002, 06:06 PM
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I agree & disagree at the same time (read: I follow Scoobynet for 2,5 years now and still don't understand this **** properly
OK, say you are making boost of 1 bar full throttle. Now, you lift off ... butterfly thingy shuts, turbo is still spinning at 170.000 RPM (
). BOV is connected to a hole thingy in yer intercooler right (later models) ? Air has no way to go, turbo starts cavitating, pressure builds up even more ... BOV sees higher pressure and ... stays shut.
On the other side of the butterfly thingy however, exhaust gasses move away, manifold pressure becomes negative (vacuum). Just like on cruise < 100 MPH...
At the same time, there's this handy hose going from the manifold to the BOV. Vacuum on one side, high pressure on the other side.
Compared to: same pressure on both sides (WOT)
So my homebrew reasoning is: it's the pressure difference that opens up the BOV
Same here BTW.
OK, say you are making boost of 1 bar full throttle. Now, you lift off ... butterfly thingy shuts, turbo is still spinning at 170.000 RPM (
). BOV is connected to a hole thingy in yer intercooler right (later models) ? Air has no way to go, turbo starts cavitating, pressure builds up even more ... BOV sees higher pressure and ... stays shut.On the other side of the butterfly thingy however, exhaust gasses move away, manifold pressure becomes negative (vacuum). Just like on cruise < 100 MPH...
At the same time, there's this handy hose going from the manifold to the BOV. Vacuum on one side, high pressure on the other side.
Compared to: same pressure on both sides (WOT)
So my homebrew reasoning is: it's the pressure difference that opens up the BOV
Same
here BTW.
29 January 2002, 06:26 PM
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Oh course you have all missed the main reason for fitting a VTA... the flames on over run
I fitted a Forge one earlier this year, to my 01. I didn't expect any difference to performance (except for the aforementioned flames ). How wrong I was. The car is definitely quicker to build boost after a gear change. This was also visible on the boost gauge.
Most of the Japanese VTAs are designed to make lots of noise and the Forge is quieter than them. If you want noise, buy a Jap one. If you want faster boost response, buy a Forge.
The re-circs work just as well, but you don't get any flames.
I fitted a Forge one earlier this year, to my 01. I didn't expect any difference to performance (except for the aforementioned flames
). How wrong I was. The car is definitely quicker to build boost after a gear change. This was also visible on the boost gauge.Most of the Japanese VTAs are designed to make lots of noise and the Forge is quieter than them. If you want noise, buy a Jap one. If you want faster boost response, buy a Forge.
The re-circs work just as well, but you don't get any flames.
29 January 2002, 06:32 PM
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OK, say you are making boost of 1 bar full throttle. Now, you lift off ... butterfly thingy shuts, turbo is still spinning at 170.000 RPM ( ). BOV is connected to a hole thingy in yer intercooler right (later models) ? Air has no way to go, turbo starts cavitating, pressure builds up even more ...
BOV sees higher pressure
This may have to wait til tomorrow as I have to leave work in a sec. Maybe Pete can set us both straight!
Here's another
for your collection m8 Whip
29 January 2002, 06:36 PM
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Whip/Evil
I think you are both correct, the small line to the back of the dump valve holds it closed during high boost, it also helps to open it at high vacuum. So when you snap shut the throttle at high boost, the pressure lifts the valve open, assisted by the vacuum behind the diaphragm.
I think you are both correct, the small line to the back of the dump valve holds it closed during high boost, it also helps to open it at high vacuum. So when you snap shut the throttle at high boost, the pressure lifts the valve open, assisted by the vacuum behind the diaphragm.
29 January 2002, 06:42 PM
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Aaargh, Cosie, don't do this to me
As long as the pressure is the same at both sides there should be no leaking (unless you have one of these wimpy < MY99 BOV's.)
There needs to be a pressure difference before the damned Pfsst thing opens
As long as the pressure is the same at both sides there should be no leaking (unless you have one of these wimpy < MY99 BOV's.)
There needs to be a pressure difference before the damned Pfsst thing opens
29 January 2002, 07:09 PM
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Hmmmm again.
I think its more or less been covered but when the throttle is closed a vacuum is created the engine side of the throttle "butterfly", this is piped to one side of the DV, the other side of the DV has turbo pressure. ie one side negative pressure, the other posotive pressure thus causing the DV to open and dump boost pressure.
VTA DV's may alter throttle response as there springing is different and a higher percentage of boost pressure is retained in the plenumn chamber so the turbo is not building up pressure from nearly zero. It gets complicated when you start looking at comprimises between retaining boost, turbo stress, fueling problems and relation ship with wastegate control etc. and Pete Croney will defo have a lot more knowledge than I.
Just one thought though, if by confusing the MAFM into overfueling (it is basically adding fuel for the air that is being VTA) is creating flames there is a possibility that these are being ignited in the turbo housing, is this safe for long term survival of the turbo? Also will overfueling destroy any cats left fitted?
Lee
I think its more or less been covered but when the throttle is closed a vacuum is created the engine side of the throttle "butterfly", this is piped to one side of the DV, the other side of the DV has turbo pressure. ie one side negative pressure, the other posotive pressure thus causing the DV to open and dump boost pressure.
VTA DV's may alter throttle response as there springing is different and a higher percentage of boost pressure is retained in the plenumn chamber so the turbo is not building up pressure from nearly zero. It gets complicated when you start looking at comprimises between retaining boost, turbo stress, fueling problems and relation ship with wastegate control etc. and Pete Croney will defo have a lot more knowledge than I.
Just one thought though, if by confusing the MAFM into overfueling (it is basically adding fuel for the air that is being VTA) is creating flames there is a possibility that these are being ignited in the turbo housing, is this safe for long term survival of the turbo? Also will overfueling destroy any cats left fitted?
Lee
29 January 2002, 07:42 PM
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I fitted a ForgeMotorsport atmo DV this weekend, I can't believe the change its made
The throttle response seems much better, the car picks up better and returning to the gas after a gear change power is instant and strong. Not my imagination, I really noticed a BIG improvement
Had no problems with poor running, also I've managed to get 130 miles on £20 of Optimax, normally I only get 110 max! (MY00)
All these people that say, oh don't get a atmos DV....have you actually had a problem or is it just scaremongering?
Although I know the Forge's have tweaked gubbings to make things work properly.
Oh and the sound is fantastic
The throttle response seems much better, the car picks up better and returning to the gas after a gear change power is instant and strong. Not my imagination, I really noticed a BIG improvement
Had no problems with poor running, also I've managed to get 130 miles on £20 of Optimax, normally I only get 110 max! (MY00)
All these people that say, oh don't get a atmos DV....have you actually had a problem or is it just scaremongering?
Although I know the Forge's have tweaked gubbings to make things work properly.
Oh and the sound is fantastic
29 January 2002, 08:12 PM
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Mr Stream.
I'm not saying I wouldn't fit one myself you just need to consider the implications.
Not scaremongering just engineering. If the DV is set up for a good throttle response it will be retaining boost pressure which, in theory, will put added strain on the turbo, how much added strain I don't know, depends on the DV. A VTA DV that does not retain as much boost pressure would be safer for the turbo but cause greater fueling problems.
The engine management fuels for the amount of air that passes the MAFM, any air that is dumped to atmo is fueled for, this is why you end up with flames. Unburnt fuel in the exhaust system will definatly damage any cats that are still fitted.
Not too sure on this but it has also been suggested that the lambda sensor in the exhaust could pick up an over rich mixture and lean off the fuel. A lean air/fuel ratio is just what you don't need when coming back on power.
Cars fitted with standard VTA DV's have them fitted before the MAFM so there is not an issue with fueling problems.
Lee
I'm not saying I wouldn't fit one myself you just need to consider the implications.
Not scaremongering just engineering. If the DV is set up for a good throttle response it will be retaining boost pressure which, in theory, will put added strain on the turbo, how much added strain I don't know, depends on the DV. A VTA DV that does not retain as much boost pressure would be safer for the turbo but cause greater fueling problems.
The engine management fuels for the amount of air that passes the MAFM, any air that is dumped to atmo is fueled for, this is why you end up with flames. Unburnt fuel in the exhaust system will definatly damage any cats that are still fitted.
Not too sure on this but it has also been suggested that the lambda sensor in the exhaust could pick up an over rich mixture and lean off the fuel. A lean air/fuel ratio is just what you don't need when coming back on power.
Cars fitted with standard VTA DV's have them fitted before the MAFM so there is not an issue with fueling problems.
Lee
30 January 2002, 08:46 AM
#24
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Cheers for clearing that up Lee 
I feel much happier now
Has anyone actually ever had any damage that's been proved or even likely caused by having a DTA valve?
I feel much happier now
Has anyone actually ever had any damage that's been proved or even likely caused by having a DTA valve?
30 January 2002, 09:09 AM
#25
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VTA before the MAF ??? Lee, I don't think a MAF would have much purpose here.
I fitted one of these, just to see if the rumours were correct...
1) The ECU meters fuel according the air that is passing the MAF (note the present tense)
2) It does not remember how much air has passed recently and does not have an algorithm to calculate some sort of balooning of the manifold.
3) A Lambda sensor looks at how much oxygen is in the exhaust gas, not how much fuel. The oxygen level doesn't change if the gas contains some fuel vapour.
4) The dumpvalve opens via a vacuum driven diaphragm, not manifold pressure (unless its broken). The vacuum is in the inlet manifold by created by closing the butterfly.
I fitted one of these, just to see if the rumours were correct...
1) The ECU meters fuel according the air that is passing the MAF (note the present tense)
2) It does not remember how much air has passed recently and does not have an algorithm to calculate some sort of balooning of the manifold.
3) A Lambda sensor looks at how much oxygen is in the exhaust gas, not how much fuel. The oxygen level doesn't change if the gas contains some fuel vapour.
4) The dumpvalve opens via a vacuum driven diaphragm, not manifold pressure (unless its broken). The vacuum is in the inlet manifold by created by closing the butterfly.
30 January 2002, 09:21 AM
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just adding my .02p
I cannot give individual component mod reviews because
TSL fitted a Forge to my MY01 at the same time ScoobySport DownPipe/decat exhaust and ITG filter. The whole thing is very intergrated, easily a match for PPP IMHO.
Eibach springs and geo setup was done at the same time, so more of MY01 -> MY04 upgrade!!!!
v. happy
rich
I cannot give individual component mod reviews because
TSL fitted a Forge to my MY01 at the same time ScoobySport DownPipe/decat exhaust and ITG filter. The whole thing is very intergrated, easily a match for PPP IMHO.
Eibach springs and geo setup was done at the same time, so more of MY01 -> MY04 upgrade!!!!
v. happy
rich
30 January 2002, 09:23 AM
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The only problem you may have with a VTA is if it leaks air in on idle. This is caused by the fact there is a high vaccum in the plenum chamber and this may cause the valve to open slightly and leak air into the inlet system. The MAF sensor won't have accounted for this air in its fuelling calculations and so you may run lean on idle and it all turns very lumpy.
There are various valves around that use double springs or a dual acting valve that get around this problem.
Andy
There are various valves around that use double springs or a dual acting valve that get around this problem.
Andy
30 January 2002, 09:40 AM
#28
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Looks like I was wrong!! No change there then!
Pete - are you saying that fitting a VTA like the Forge won't create fuelling problems? Is this true of both the classic and new-age scoob?
Whip
Pete - are you saying that fitting a VTA like the Forge won't create fuelling problems? Is this true of both the classic and new-age scoob?
Whip
30 January 2002, 10:31 AM
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I've got a Forge VTA (thanks to TSL ) and it doesn't appear to cause problems as such... I am uprating the spring so it doesn't let go quite so quickly when you start to let off, as this IMHO is causing increased engine braking, which I don't want... the spring to help the dv to retain more air in the turbo as I begin to let off, thus less of sudden effect... oh.. and it might sound sort of rally car esk chattery
) and it doesn't appear to cause problems as such... I am uprating the spring so it doesn't let go quite so quickly when you start to let off, as this IMHO is causing increased engine braking, which I don't want... the spring to help the dv to retain more air in the turbo as I begin to let off, thus less of sudden effect... oh.. and it might sound sort of rally car esk chattery
30 January 2002, 11:51 AM
#30
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Whip,
The only way you will get any fuelling problems is if the BOV leaks and lets unmetered air into the intake. If you get one that doesn't leak under high vacumm then you will not have any fuelling problems.
Andy
The only way you will get any fuelling problems is if the BOV leaks and lets unmetered air into the intake. If you get one that doesn't leak under high vacumm then you will not have any fuelling problems.
Andy