Hot Chicken

Can anyone help. On my WRX I have a vent to air Dump Valve which apears to be working well. However I was reading an artical on another scooby web site and this guy did not recomend them as they can cause engine trouble. I was just intrested to hear your thoughts.
Thanks

Hot Chicken

Can anyone help. On my WRX I have a vent to air Dump Valve which apears to be working well. However I was reading an artical on another scooby web site and this guy did not recomend them as they can cause engine trouble. I was just intrested to hear your thoughts.

Thanks

ALi-B

iTrader: (1)

He's right. Yes they cause problems, Simply put: -

The engine uses an airflow metre that measures the air going into the engine...this works out how much fuel it needs.

Normally a Recirc dumpvalve recirulates the air, so no extra air is drawn in.

With a vent to atmosphere dump valve, when it is open, extra air will be drawn through the airflow metre, making it think the engine is sucking in more air that it actually is. This confuses it and messes up your fueling momentarily every time you change gear. Also if you have a weak/badly adjusted spring, it maybe open at idle. This will make the engine idle unevenly.

Many people ignore the above reasoning. Some just don't know any better and want a noise. I'd seriously question anyone who reccomends a vent to atmosphere dump valve, especially when they give absolutely no performance advantage.

Aztec Performance Ltd

iTrader: (234)

If it works then I wouldn't worry about it.

Never had any probs with mine and the momentary over fueling does the car no harm and gives nice pops and bangs and :flames: (mainly from SN community )


Bob

Elmer Fudpucker

I'm at a complete loss as to why people bother to fit this kind of engine mod to their car

I defy anyone to tell me that their maf equipped Subaru runs better with a vta dump valve fitted.Let alone enjoy the cacophony of stupid noises that accompany it

re-fit your standard dump valve young man, and 'marvel' at your engines regained throttle response and smile smugly to yourself at traffic lights as your vehicle will now idle as it was intended to

Olly Powers

I would get some proffesional advise as the opinions given here are absolute claptrap.

The purpose of the VTA is to allow the expulsion of built up pressure which would otherwise act against the spinning turbo, hence less lag between shifts when you have one fitted. If it idles badly or doesn't improve spool up then its defective.
Check the spec of any big power car you like and you will see that they have a VTA. If you get the chance, ask them why its on there if its so useless.
VTA doesn't draw air in either, it lets metered air out which causes the overfuelling (which isn't bad for your engine)
Do your research boys instead of just repeating stuff you heard on here.

Aztec Performance Ltd

iTrader: (234)

As much as I like VTAs your defence is flawed.....the car comes as std with a dump valve (re-circ) which does all of what you mention.

Bob

Olly Powers

Your right Bob recircs do the same job, so why do they sell VTA's and what is their purpose (and don't say its just for the noise, cos £300 for a whoosh is a bit excessive)

Aztec Performance Ltd

iTrader: (234)

They sell them because they can and because not all cars are MAF based. Also dv range from under £100 to around £300. The dearer ones have a superior multi-valve system but also come with (optional) re-circ kits for MAF based cars.

Mind you....after all that I still have a HKS SSQV which I have on VTA

Bob

Dark Blue Mark

Olly, Elmer and Ali B are not talking "clap trap", I cant believe you can come on here and say that when you clearly don't know a thing about the Impreza

Ive tried them on various Impreza's and had no probs other than the overfuel and impact on MPG. A badly fitten one can leak and cause idle probs., and believe the APS one doesn't have a good reputation for this. I personally dont like them but each to their own, and Bob's counterargumet is also spot on.

MB

ALi-B

iTrader: (1)

I could go to say that a badly adjusted/cheap aftermarket dumpvalve can induce alot of chattering when used off-boost or low boost. (both aftermarket recirc and vta's). Doubt any harm would come of it (unless we talk very long term), but it doesn't sound too clever.

Tone Loc

iTrader: (1)

Sorry but the above is wrong. The car and ecu is never confused and a VTA does not cause more air to be drawn in. The MAF measures the amount of air going into the engine and thus calculates the load from this. From the fuel table it looks up the time to open the injectors from the given load and rpm.... and fuels accordingly. When you lift off the DV dumps the air that was supposed to go into the engine...... i.e the air that the ecu has just fuelled for. So either VTA or recirc the air has not gone into the engine where the ecu has just opened the injectors for. So you get a rich AFR when you lift off for either VTA or recirc (this is not overfueling, it's a fact that there is less air than expected and not more fuel). I have wideband logs of this for standard DV, Forge recirc and Bailey VTA. All cause rich AFR on lift off and the AFRs are not that different, but the VTA was ever so slightly richer.

Personally i have gone back to OEM recirc (with MAF and Apexi Power FC) due to this providing a slightly 'smoother' on/off throttle behaviour mid bend and the noise got annoying. The overfuelling is simply not true and if a VTA causes increased MPG it's either defective or you are driving harder to here it whoosh, a fully working one will not have any of those effects compared to the OEM DV.

Tony.

Elmer Fudpucker

how the hell is that 'clap trap'?.....when its based on my personal experiences,when experimenting with a VTA dumpvalve on my first Impreza with a very close friend who works at 'a' place where they manufacture the bloody things

Hot Chicken

Mmmm it seems that my question has sparked a bit of a debate. I do have to say that since I fitted my Forge Motorsport VTA dump valve about 6 weeks ago, the scooby seems less resposive and the MPG is not as good as it was. I'm obviously no expert on dump valves but after spending 110 quid on the thing I cannot realy see any benefits. And the noise is starting to **** me off a bit!
I think I may end up sticking it on Ebay and going back to the orginal.

ALi-B

iTrader: (1)

I think you misinterpreted what I wrote - I was speaking in laymens terms to try and keep the technicalities out of it and try and get some understanding for people not so conversent in Efi control systems.... "drawn into engine" I did not mean the actual engine itself, more so the engine as a unit - including the induction, turbo and inlet tract. "Confused" meaning behaviour that is unwanted or not ideal.

ATM valve is open letting air out....so where is the air getting drawn in???
Through the the air intake...what's in the air intake? a Maf sensor. Granted on closed throttle you'll get an overun fuel cutoff. And what's the harm, nothing much....But tell me this, do you purposely drive round with an injector disconnected because you like the lumpyness?

Hot Chicken - yes there is a big area of criticism over dumpvalves...just go with the flow

TonyBurns

iTrader: (3)

You want to speak to Bob Rawle at BR Developements, he can give you a clear perspective of how these VTA DV's work, but AFAIK, when you get the rich mixture, the ecu sees this and then compensates, the trouble is, when it compensates, it puts more air in so it leans you out, good if your car is mapped for it, not good if it isnt, but you will gain nothing from a VTA in performance, except a wooooooosh sound.

Tony

Tone Loc

iTrader: (1)

Tony, the rich mixture is there for a fraction of a second (as indicated by my wideband logs). This is also off throttle so IDC = 0% (fuel cut). As soon as you get back on throttle the 'richness' has gone and thus the ecu should not (or mine doesn't/didn't) react to this. This can be seen on the AF correction logs. Also interested in how you say the ecu can put more air in??????? Isn't that controlled by your right foot???

I do agree that VTA gives NO performance increase at all. But these horror stories of huge increas in MPG, terrible idle and bore wash simply shouldn't happen if the VTA DV is good quality and not broken.

Tony.

P.S i'll say again that i use a recirc DV so i'm not biased

Hot Chicken

Thanks for all your imput to my original question. Just to up date you all. I took of the Dump Valve today and have to report that the car seems to run better with out and with no silly noises.

My advise would be save your money as stick with the standard one.

scoobypreza

I also put my standard re-circ back on today and my car, MY98, definately runs better, it pulls and runs smoother.
It's weird now when you change gear and all it quiet!!

Dave