Dump valve needed ?

E

emery1990

Tuner
Points
60
Location
portsmouth
Car
A3 1.8T quattro
My brother tested out my new car and mentioned it had a quite a bit of lag. After this i started to notice it more, I then done some research and found various sources stating that a dump valve would get rif of almost all of the lag due to releasing excess pressure, as you all probbaly no anyway :). I was looking at the re-curcalating dump valves as they dont make the " unnnnnnnnnn chhhh" sound. Also saw a few sources saying it is an essestial mod for the vag 1.8t engines.

Has anyone else added a dump vale to get rid of lag. ? ive seen them for £80 so far, plus £40 for the kit.
 
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It'll have a dump valve of sorts as standard, otherwise your turbo will wear out very quickly. No way will changing it get rid of all of your lag, or even a large amount tbh so wherever you read that, stop visiting those sites.

Lag is just something you have to learn to live with on a turbo car. Just change down a gear or two if you need booooost. I've never driven one but I'll bet my left testacle there's very little lag on these 1.8T VAG engines. Your brother probably doesn't know the meaning of lag.
 
I'm surprised that you find that car laggy. My mate has a 1999/T plate one and the turbo is very very discreet indeed. It's just there on demand.

My car has a VGT and even that can feel a bit slow to spool up if you catch it out at very low revs.

With the 1.8T Volkswagen units you should barely notice that the turbo is there to be honest, it's that discreet.

I suspect you have a different problem altogether. CHeck with PGARNER he's the VAG man but I reckon it's a gummed up EGR valve.

Cure. Firstly - can of Forte Gas Treatment in tank. Stick a dozen litres or so of high quality unleaded on top.

Now you go and drive the nuts of the thing for an hour or so.
 
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well then you cant say nothing about the car then really. he does no alot about cars.

and hdi fun, yer it isnt really bad but i dint notice it as im not as experienced, he just said that there is some lag about. Just wanted to know if upgraded the dump valve would get more pressure out quickly.
 
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Aint here mate, he just said get a remap. I just bought a bottle of that stuff from ebay for £8, so ill put that in once i get it back. car in garage as they found a cracked brake hose ! I know the turbo has got like dump valves on them already but like most things wouldnt upgrading them do a better job. ? eg a dump valve that realeses pressure far quicker and handles larger pressure.
 
upgrading the dump valve depends on the original equipment. I've got one on the Scooby, the original one, and bought a Blitz one to replace it with but was advised by the specialists not to bother unless doing major engine work as the original ones are perfectly effective
 
I doubt that a dump valve will address the lag issue, unless the old one is sticking open and partially venting the boost.

The turbo should start to spool up around 1500rpm. A remap will get it spooling up a bit quicker than that.

Do a few 0-60 runs in a safe quiet private road and see if you get near the quoted manufacturers figures. It could be down to a worn turbo. You didn't notice till your mate said anything so I doubt there is much wrong to be honest.
 
I suspect what your mate has noticed is the apparent lack of boost altogether. The 1.8T is very discreet with its turbo, it more or less just ramps up the whole torque curve across the whole rev range with there being no noticeable 'boost' point as such.

If the turbo is worn then you'll have clouds of smoke from the exhaust under acceleration.
 
Dump valves or waste-gates,

don't affect lag. In normal operation they are closed allowing boost to build-up with rpm and blow-off or dump the excess pressure at a set value (which is another way of saying they stop any further power build-up).

Lag will depend on installation, and whether it is leak-free and in good working order.

All turbo systems have some lag. It is minimised by using smaller sized turbos (which spin up faster than larger ones) and the length of inlet piping.
Intercoolers and long intake piping also increase lag.
Restrictive exhausts also contribute to the delay in throttle response.

Try another similar specced car if you can determine if it is something common with the type or whether it may be a fault with your particular car.
 
So if a dump valve doesn't help lag then what were they produced for?
A dump vavle releases pressure around the Turbo when you lift off the accelerator. (Ie to change gear.) This release in pressure allows the Turbine to continue to spin thus reducing turbo lag. They are there for a purpose. Now i'm not saying the standard unit isn't good enough. But there is always room for improvement on standard applications.
 
You shouldn't need to do that with the engine we're discussing. The engine was designed from the ground up with a view to supercharging and the whole lot integrates very well.

There was a 20v non-turbo version around in the Passat for a while but it was never very popular.
 
turbonutter69 said:
So if a dump valve doesn't help lag then what were they produced for?
A dump valve releases pressure around the Turbo when you lift off the accelerator. (Ie to change gear.) This release in pressure allows the Turbine to continue to spin thus reducing turbo lag. They are there for a purpose. Now i'm not saying the standard unit isn't good enough. But there is always room for improvement on standard applications.
Click to expand...

Some slight confusion here.

A traditional waste gate or dump valve is not connected in any way to TPS. It is a pressure sensor. All it does is open at a specified or set amount of pressure to limit the amount of boost.

The type of system you may be thinking about is this:-

http://www.balancemotorsport.co.uk/main.asp?sitepages=dumpvalves
 
turbonutter69 said:
Thats just about what I said in that link.
The thread is about Dump Valves.
Click to expand...

Yes, I'm aware of that thanks.

There are different types of dump-valves, just as there are different names for the same thing:- waste-gate, blow-off valve, etc.

A traditional turbocharger system runs a waste-gate. It does not bleed air off until the actuator senses the boost pressure the system is limited or set at.
VAG amongst others modified this straight-forward simple operation and complicated the system for customer please-ability issues by bleeding air off at idle and in the cruise/over-run.
This type of advance in technology is a backward step for car enthusiasts as this type of operation bleeds air off continually, which slows the throttle response even more than a traditional turbo set-up which doesn't do this. It is exactly what they are explaining in the link which is provided to help the original poster, .......if you don't mind, that is.
 
Sid447 said:
Yes, I'm aware of that thanks.

There are different types of dump-valves, just as there are different names for the same thing:- waste-gate, blow-off valve, etc.

A traditional turbocharger system runs a waste-gate. It does not bleed air off until the actuator senses the boost pressure the system is limited or set at.
VAG amongst others modified this straight-forward simple operation and complicated the system for customer please-ability issues by bleeding air off at idle and in the cruise/over-run.
This type of advance in technology is a backward step for car enthusiasts as this type of operation bleeds air off continually, which slows the throttle response even more than a traditional turbo set-up which doesn't do this. It is exactly what they are explaining in the link which is provided to help the original poster, .......if you don't mind, that is.
Click to expand...

But what if I do mind. ;) :lol::lol::lol:
 
Pressure build-up needs to be released from the system when the throttle is closed to prevent turbo stall. This is what a dump valve (be it re-circ or atmos) is for. Doing so keeps the turbine blades spinning, meaning boost is slightly more readily avaliable when you're next on the throttle. Thus, lag is reduced in this way, when compared to not releasing this pressure whatsoever.

A dump valve is NOT there to stop any further build up of boost past a certain level. That's what a wastegate actuator is for. Enjoy.
 
MasterAuron said:
Pressure build-up needs to be released from the system when the throttle is closed to prevent turbo stall. This is what a dump valve (be it re-circ or atmos) is for. Doing so keeps the turbine blades spinning, meaning boost is slightly more readily avaliable when you're next on the throttle. Thus, lag is reduced in this way, when compared to not releasing this pressure whatsoever.

A dump valve is NOT there to stop any further build up of boost past a certain level. That's what a wastegate actuator is for. Enjoy.
Click to expand...

Thank you for explaining this properly. It's also the reason that diesel engines don't need dump valves - there's no throttle to restrict the air intake.
 
And then you have the debate of whether a dump valve actually helps (argument of releases all the air in the system that the turbo then has to build back up when throttle is applied vs allowing the compressor wheel to continue spinning.)

Let alone the argument for if you need a dumpvalve (will it cause damage...my opinion at low boost <1 Bar its fine)

Oh and the good old where to place the dump valve (at compressor outlet vs just before the throttle body)

It all gets very detailed :lol:
 
Munday said:
And then you have the debate of whether a dump valve actually helps (argument of releases all the air in the system that the turbo then has to build back up when throttle is applied vs allowing the compressor wheel to continue spinning.)

Let alone the argument for if you need a dumpvalve (will it cause damage...my opinion at low boost <1 Bar its fine)

Oh and the good old where to place the dump valve (at compressor outlet vs just before the throttle body)
Click to expand...

When you get turbo stall the air is usually lost anyway mate as it rushes back out through the filter (fluttering noise). A recirc obviously returns the air pre-turbo.

Turbo stall is fact. I think the true argument is whether it actually damages your turbo or makes it wear out any faster.

As for the placing I'm a firm believer it makes naff all difference in reality. I can't be arsed to go into the theory of both positions.
 
dsc4138vp2.jpg
 
A petrol engine doesn't necessarily need this bleed-off system either,

A turbocharger compressor doesn't stall as in stop or slow down (there's serious inertia in a turbo spinning on the far side of 50,000rpm) it is being driven by exhaust gas pressure that has a lot more energy behind it than static air in an intake system with the throttle closed.
It is the compressor blades that experience aerodynamic blade-tip stall and this doesn't cause any mechanical problem. It just makes a repeated popping sound.

Anyone remember the early days of the Audi Quattro rally cars etc where this was part of their signature sound along with the turbo waste-gate woosh, dumping excess boost pressure to atmosphere.



This was all deemed to be un-acceptable and too crude for production road cars, they wanted quiet operation of the turbo and better drivability with nice manners for the average "Miss Daisy" and "Joe Bloggs" so the by-pass systems were developed and productionised.
 
Rally cars don't use dump valves these days though do they? Thats why you get that chirp from rally cars. It's the pressure trying to go back into the turbo.
 
turbonutter69 said:
Rally cars don't use dump valves these days though do they? Thats why you get that chirp from rally cars. It's the pressure trying to go back into the turbo.
Click to expand...


I'm not sure what system they use now,

The technology is not so exciting anymore. Limited boost and air-restricted with computer control of most parameters.

Just doesn't seem as interesting to one and all like the fire-breathing 800hp rally cars were back then. :(
 
Lots of cars use thottle plate dampers to reduce NO2 emissions when the pedal is suddenly released. This might help.

A VGT will help as well.
 
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