15 replies to this topic

[Joe-Turbo]

was just having a look at courtenaysports website and noticed they will now fit an after market dumpvalve?
Thought they where not recomemded (due to loss off performance?)

"Dump Valve Information
Dump Valve Fitting Recommendations
This is a guide for fitting a dump valve and eliminating dump valve related drivability issues on Astra G and H, Zafira A and B and VX220 fitted with the Z20LET - LEL – LER - LEH engines.

The dump valve for these engines must be a twin piston unit as the car has air mass metering. The twin piston unit stops the valve breathing un-metered air on vacuum, confusing the engine ECU.

How a Dump Valve Works
Traditionally a dump is fitted in the boost pipe close the inlet manifold; it has a vacuum - boost trigger pipe taken from the inlet manifold between the throttle body and the engine. When driving the car hard on boost there is boost pressure pushing on the dump valve, however there is equal boost pressure pushing on the dump valve diaphragm on the other side. This holds the dump valve shut in equilibrium. When you lift off the throttle the throttle body closes this creates a vacuum in the manifold thus in the boost – trigger pipe, this vacuum pulls on the dump valve diaphragm and with the boost pressure in the inlet pipe pushes the valve open releasing the air into the engine bay with a whoosh.

How is this Vauxhall Engine Different ?
These engines work as above, with one major difference. The boost - vacuum trigger pipe is run through a vacuum storage capsule, and a solenoid that is triggered by the engine ECU. There are switches on the pedals so the ECU knows when you de-clutch and trips the solenoid to create the vacuum quicker to the original equipment recirculation dump valve built into the side of the turbo.

This vacuum solenoid arrangement is also used on part throttle to regulate the air mass to the engine, i.e. when the turbo is trying to make boost due to its small size but the load demands and throttle angle do not require boost, it opens and shuts the factory re-circ valve to regulate boost improving drivability, kind of like a secondary throttle.

This is the source of the trouble. If you use this trigger source (i.e. from the original vacuum storage) for the aftermarket dump valve it will pulse the new valve on part throttle, the previously metered air is then released into the engine bay and will cause driveability issues on the fuelling. In some circumstances the car will also go lean, in this situation the TC (traction control) light can come on.

The Fix
The cure is to give the aftermarket dump valve its signal from a true non interrupted vacuum source; we recommend the fuel pressure regulator. For further improved driveability, it is possible to leave the original equipment valve still working so the engine management can regulate, control and pulse this valve. However the aftermarket valve will operate slightly quieter.

[CupidKnewRap]

the factory re-circ valve regulate(s) boost improving drivability, kind of like a secondary throttle.

I don't understand.

why would you replace the re-circ with a standard dump valve?

[urbanmac]

the factory re-circ valve regulate(s) boost improving drivability, kind of like a secondary throttle.

I don't understand.

why would you replace the re-circ with a standard dump valve?

sorry to be the thick kid but apart make the car sound like boy racer scooby what do they actually do?

[nakajima]

its suppposed to "dump" the forced air instead of going back through the intake and back through the turbine. sounds a tad chav imo. the only noise i like from a turbo car is a proper wastegate chatter

[colgy]

its suppposed to "dump" the forced air instead of going back through the intake and back through the turbine. sounds a tad chav imo. the only noise i like from a turbo car is a proper wastegate chatter

Isn't 'wastegate chatter' a myth? Isn't it just pressurised air being forced backwards after hitting the closed throttle, then being chopped up by the compressor? I'm far from an expert, but I've heard so many different things! Any automotive engineers out there?

[MikeF]

a decent dumpvalve should also stop the turbo stalling afaik

[paulf-cam]

a decent dumpvalve should also stop the turbo stalling afaik

This is in fact the only job a dump-valve is designed to do (apart from the chav ones which whoosh as well)

Of course, the VXT has a dump-valve installed as standard, its just that you can't hear it because of the airbox.

Cheers, Paul.

Isn't 'wastegate chatter' a myth? Isn't it just pressurised air being forced backwards after hitting the closed throttle, then being chopped up by the compressor? I'm far from an expert, but I've heard so many different things! Any automotive engineers out there?

Its seems that the noise you are describing ought to be called wastegate chatter, because it sounds like a pretty good description of the noise, but i'm told 'wastegate chatter' describes something completly different!

Dunno what, like!

Cheers, Paul.

[Richy]

IIRC There are some VX owners that have run a dump valve with no problems.

[VXT Tim]

I'd be all up for an uprated dump valve. Not so keen on one that comes with a PPPTTTSSSHHHHHHHH everytime i change gear though... chavtastic!

[Thorney]

We wont fit them and wont remap a car if it has one fitted. The VXT doesn't have a VTA dumpvalve but an internal re-circ valve which is built into the turbo. The engine was deisnged for this, the turbo was desinged for this and swapping out a VTA (vent to atmosphere) valve will AT BEST give you the noise but more likely will drop your power, make it lumpier and cause running issues. Sorry.

[covert ops]

Sorry 'Dump Valves'

Right now i'm pmsl.

Not the concept...... but had an old (H reg?) Skyline beside me the other day, and we were stuck in stop/start traffic.

EVERY free 50M was a challenge to see how may times he could get that 'swoosh' sound
(Along with continual revving and general harrassment like he was trying to cut into my lane )
While scouring the traffic to see if he'd earned our respect

We both turned off and after more harrassment, hit some twisties on a A road.
Quick wink to the gf (she knows what that means/ hold tight) and didnt see the W*nker again.

Still laughing at the concept that 'the noise' would scare me out of my lane or that in some ways i didnt give him enuff respect!!
He also had a flowerpot exhaust just incase I missed it.


Sorry back on topic

Regardless of any potential gains/losses I wont be fitting one as the noise is quite......annoying. IMO
And I Have an NA
Andy

Edited by covert ops, 12 July 2006 - 03:58 PM.

[jasvxt]

Fook me not dump valves again for gods sake leave well alone. Spend your money on something worthwhile like a zorst or full tank of petrol and go for a blast. The cars noisy enough in all the right places anyway. Why give your vxt torrets. Dump valves wannnnnnnnnnnnnkers. imo

[VXT_SI]

When I bought my car it had a Bailey DV fitted, never had a problem with it, but never really liked the noise..... Does anyone have a copy of the fitting instructions so I can follow them in reverse order? From what I understand you have to some how jam the OEM DV closed when the bailey one is fitted, does anyone know if this causes any problems when returning to standard?

[cragpuss]

When I bought my car it had a Bailey DV fitted, never had a problem with it,
but never really liked the noise..... Does anyone have a copy of the fitting
instructions so I can follow them in reverse order? From what I understand
you have to some how jam the OEM DV closed when the bailey one is fitted,
does anyone know if this causes any problems when returning to standard?

Same here I have just been a bit embareced to ask before

[Joe-Turbo]

im not after a replacment dump valve myself, just wanted to give you guys the info. just out of interest is the dump valve the same on the astra vxr hybrid turbo as the standard one? cragpuss/vxt_si, im sure you can get it back to standard (bit of a pain, think you need a part from vauxhall, could be wrong though) , I remember some one else writting about it a while ago, do a search joe

Edited by Joe-Turbo, 13 July 2006 - 01:04 AM.

[MAP18W]

was just having a look at courtenaysports website and noticed they will now fit an after market dumpvalve?
Thought they where not recomemded (due to loss off performance?)

"Dump Valve Information
Dump Valve Fitting Recommendations
This is a guide for fitting a dump valve and eliminating dump valve related drivability issues on Astra G and H, Zafira A and B and VX220 fitted with the Z20LET - LEL – LER - LEH engines.

We published this information for people who contact us regarding issues with the fitment of an aftermarket DV. We have never fitted a DV to a VXT. We do not list the DV on the VXT page on our site, but the info is published mainly for Astra/Zafira owners who have experienced problems. We included the VXT in the info we published because it has the same Z20LET engine and there are VXT's out there with DV's fitted. A correctly fitted DV will not cause a loss in performance unless there is a problem with the DV i.e. it is leaking off pressure therefore reducing boost.