Dump valve question!!!

[fataudifella]

Hi All,
New member as ya can see,Just bought an A3 1.8T MY98..Nice car,drives well and does everthin you would expect.Now,was gonna fit a "vent to atmosphere"DV but read on here last night that it can cause a loss of 7bhp?
I've had a good think about this today and cant think why this would be.ok maybe create a flatspot,maybe even a stutter,but as far as im concerned the only difference is when on closed throttle the excess air will be pushed into the inlet pipe[with OE DV].The AFR in turn expects this whoosh of air and richens the mixture up to compensate..so from what i can see the VTA DV doesnt do this..ie..car will go rich on overun,just more than normal.
So to conclude,when car under full power,the dump valve doesnt even come into play,so how is it droppin this BHP?
Im confused,can anyone fill me in with the technicalities here?
BTW,must have fitted 10-12 VTA DV to my own cars over the years and fitted loads for friends and customers and have never heard a power loss mentioned before.
Thanks all,
Gary

 

[Ess_Three]

Think of it as lag rather than loss.

With a re-circulating DV each time you lift off you dump the already compressed air back into the air inlet tract just downstream of the turbo.

Whith an atmospheric, you dump it to the engine bay.

When throttle is re-applied, the turbo has less work to do when a re-circulating DV is used as it already has the advantage of having slightly pressurised air heading towards the turbo, so that it takes less time to fill the air inlet system with pressurised air, and hence less time to get the boost into the engine.

The figure of 7BHP was found by AmD. I have no proof one way or the other if this figure is accurate in all instances...but regardless of the figure, the fact that there is noticable lag is proven - as has the fact that a re-circulating type of set up is more efficient.

Regardless of the figure (7 BHP) this is not at peak power...it is lower down the rev range...near peak torque - or the point of maximum boost.
You'll not loose peak power with an atmospheric dump valve...but you will loose drivability and throttle response in the form of increased lag.


It seems slightly odd to me that people are dead set on adding atmospheric dump valves when all evidence suggests they are actually decreasing performance...which kinda goes against the whole 'tuning' ethos, does it not?

There's also the whole issue of throwing a 'Check' light on...the ECU looses air and confuses it's self.
Some get it with an atmospheric DV...others don't.

Not all cars respond the same...but VAG cars do seem to be touch and go on the running of atmospheric DVs.


Perhaps the noise is what people want...to each their own.

 

[Stuart_A3_Turbo]

The age old debate - atmospheric DV's. Ive got one, i love the sound, maybe it does increase lag but then again ive also suffered no problems with it. I like mine and wont change it even if it does lose a small amount of power.

Ess_three - It does not go against the whole tuning idea, it all depends how you look at the word 'tuning'. If you want to call tuning as gaining every bit of power and torque you can then fair enough. I dont however, i see it more as gaining power to the point im happy with as at the end of the day, i dont go racing the car everywhere i can so whats 7bhp to me? Nothing at all mate. If i was building a track day car, pure 1/4 mile sprint car then sure id go for recirc but for every day driving it makes no difference at all /ubbthreads/images/graemlins/laugh.gif

 

[fataudifella]

Like ya say.drivin is drivin........but it was the 7 bhp thing......i was thinkin,well if its off throttle base no DV is playin any part........that is a simplyfied idea i know........but in real terms its right...but i reckon.....if 2 cars were the same apart from dump valves there would be nothin in it!!!!!!!!ever!!!!!!!!!Bet im gonna get slated........but,apart from noise.looks,etc etc...does anyone have any real evidence that a VTA DV is doin any harm????

 

[Ess_Three]

[ QUOTE ]
Stuart_A3_Turbo said:
Ess_three - It does not go against the whole tuning idea, it all depends how you look at the word 'tuning'. If you want to call tuning as gaining every bit of power and torque you can then fair enough. I dont however, i see it more as gaining power to the point im happy with as at the end of the day, i dont go racing the car everywhere i can so whats 7bhp to me? Nothing at all mate.

[/ QUOTE ]

Well 'Tuning' to me is mofifying to improve things...
Not changing for changes sake...which is why I still have a standard airbox for instance.

If you are 'Tuning'...as in improving...but knowingly loosing a known amount of power (don't get hung up on the whole 7BHP figure) or some drivability...I wouldn't call it 'Tuning'

I'd call it 'Restricting'
Or 'De-Tuning'
Or 'Downgrading'

It's not about making big numbers...it's about making it better.

If it's not better, then it's worse. Surely thet's the case?
So who in their right mind modifies a car knowingly making it worse?

Not me...that would plainly be stupid.

 

[Ess_Three]

[ QUOTE ]
fataudifella said:
Like ya say.drivin is drivin........but it was the 7 bhp thing......


[/ QUOTE ]

Don't get hung up on 7BHP...
There is a loss - or an increase in lag...look at it whichever way you choose.


[ QUOTE ]

i was thinkin,well if its off throttle base no DV is playin any part........that is a simplyfied idea i know........but in real terms its right...


[/ QUOTE ]

No, off throttle there is no difference.
But as soon as you re-apply throttlle there is...the R DV picks up faster than the A DV.
That's not a rumour..it's fact...it's simple physics.

The amount of difference is debatable...but there is a difference, and the R DV is the faster to return to full boost....therefore the area under the power / torque graph is larger...therefore the car is faster.

Basic physics...


[ QUOTE ]

but i reckon.....if 2 cars were the same apart from dump valves there would be nothin in it!!!!!!!!ever!!!!!!!!!Bet im gonna get slated........but,apart from noise.looks,etc etc.


[/ QUOTE ]

We don't all drive in straight lines, flat out.

If you have to drive a road rolling on-off throttle, getting back onto peak torque faster will offer an advantage...surely everyone can see that?

Better throttle response, less lag, more area under the graphs...faster car.

In a straight line, you're right. Very little in it.


[ QUOTE ]

..does anyone have any real evidence that a VTA DV is doin any harm????

[/ QUOTE ]

Harm? Define harm?
It's not doing any harm...except maybe the odd check light.

If the ECU's not happy, it'll shut down...limp mode...very slow!

An atmospheric DV doesn't do harm...and it's a perfectly good system. However, on a 1.8T there is an improved system, and one the management system is designed for...and that's to re-circulate.


At the end of the day...if you want the noise...do it!
It's your car...it'll not harm anything.

Personally, I can do without the noise so loved by pimply schoolboys having wet dreams over be-winged Imprezas...and I can do with the extra performance / throttle response / reduced lag offered by a recirculating system.

But there again, my car's for driving. Not posing / impressing little boys & girls. /ubbthreads/images/graemlins/tongue.gif

To each thier own...
Some people like the noise...and you don't always get a CEL - I don't believe Stuart has any problems.

Try it and see...
You have all the information you need to make an informed decision...

 

[Stuart_A3_Turbo]

Ess_Three, i fully agree with what you are saying. I have no doubt that the recirc is far better performance wise. What im saying, is i have tuned our car to around 230bhp ish and i dont use all this power every day. Day to day driving, it makes no difference at all and i certainly dont do it to impress anyone. If i was, id go for recirc to impress people on here. If i was going out day to day, racing every car on the road then without a doubt its recirc all the way. Thing is, do you believe it is important to have every ounce of power possible, aqs little lag as possible for day to day driving? I cant see how it would be needed unless you really hammer your car everywhere. As you have said 'each to their own' we all have different opinions.

Lets agree to disagree with this one eh /ubbthreads/images/graemlins/laugh.gif

And yes, your right, ive suffered no problems, only limp mode once due to a seperate fault on the car nothing to do with the DV.

 

[Ess_Three]

[ QUOTE ]
Stuart_A3_Turbo said:
What im saying, is i have tuned our car to around 230bhp ish and i dont use all this power every day.


[/ QUOTE ]

That must be one hell of a spec of A3 if you are making 230BHP!


[ QUOTE ]

Thing is, do you believe it is important to have every ounce of power possible, aqs little lag as possible for day to day driving? I cant see how it would be needed unless you really hammer your car everywhere. As you have said 'each to their own' we all have different opinions.


[/ QUOTE ]

No...and the DV doesn't affect peak power anywqay...which is the important factor if you are hammering it everyday...

But minimum lag and maximum throttle response are important to me...that, I do need every day.


[ QUOTE ]

Lets agree to disagree with this one eh /ubbthreads/images/graemlins/laugh.gif


[/ QUOTE ]

No problem...it would be a sad place if everyone were the same. /ubbthreads/images/graemlins/beerchug.gif

 

[Ess_Three]

[ QUOTE ]
BIGT said:

You want to go careful what impression you are throwing around of people - think this was a bit of a generalisation don't you??!! Just stick to the facts and not upset people on here!!



[/ QUOTE ]

Why?
What's gonna happen?
Are you going to start throwing your toys out of the pram?

No, I don't think that was too much of a generalisation...I'm damn sure the majority of people on here know what I'm like...That's my view and I'm entitled to it.

Buy hey! If the cap fits...



Have I upset anyone?


As for the facts...
They have been presented in full within the thread...the information is there for all to see.

 

[Ess_Three]

[ QUOTE ]
Stuart_A3_Turbo said:

We all have opinions mate and the above is Ess_Three's one. I dont take any offence to what he says cause as said, we all like different things and have different opinions.

[/ QUOTE ]

Absolutely..
At the end of the day, Stuart has done something different...and I, for one respect that.
It may not be a mod that I would choose to do...but it works for Stuart and he's more than happy to discuss it, and to offer advice to those that wish to try it.

There has been no offence meant or taken on either side...a bit of bantar is expected...and provided.

And for the record, I've heard a Bailey ADV...and it's not THAT loud! /ubbthreads/images/graemlins/smirk.gif

 

[Grant]

Arguments (or heated discussions) about ****** dump valves again! /ubbthreads/images/graemlins/snore.gif /ubbthreads/images/graemlins/lol.gif

 

[fataudifella]

Im sorry i started this thread!!!ha ha..not really,just wanted to know where i stould if i fitted one..oh yea..i aint a pimply schoolboy either..In fact the Audi is a downgrade for me,and in my opinion its a good little motor,but i think its pretty sluggish considering that its a 20v turbo.If fitting a VTA DV is gonna knock more of an edge off the performance it probably aint worth doing.
Put my cah into gettin it goin quicker i guess...anyone recommend anywhere for a remap of the ECU..without going over the top on price?

Cheers all
Gary