just for curiosity !

[arjunior45]

How does the oem dump {blow off} valve is connected?
Does the tube 'A' {see picture} goes to the 'air filter' tube and the 'B' one to the tube that connect the intercooler with the intake manifold?

PS.
sorry JimNielsen for using one of your pictures.

[Juan AR155Q4]

Nick,
B goes to air filter, and A goes to the hose that connects the intercooler with the intake manifold.
The smallest one goes directly to the intake manifold (as the vacuum gauge).

If you leave B unconnected, you will hear a nice PSHHHHHH! when you lift your throttle. Remember to block where it use to go (air filter hose).

[arjunior45]

Thanks Juan,
I just wanted to know if my ex-mechanic had done one of it's ...
And guess what? It was connected in the opposite way!
'B' to the hose that connects the intercooler with the intake manifold and 'A' to the air filter.

This morning I've replaced this oem valve with an adjustable one - I've bought it a year ago and never had the 'time' nor the 'mood' to mount it - but still need to register it. I'll do it later or tomorrow morning.
I do not know if I'll let blow free to air or keep it blow in the 'air filter' tube. I do not know if I'd like the 'PSSSSSS' sound. Will see.

[arjunior45]

Found this in the manual.
So, I believe the connection were correct for my 'stall prevention' valve.

[AlfaJack]

Found this in the manual.
So, I believe the connection were correct for my 'stall prevention' valve.

The arrows on that diagram do not seem right to demonstrate air flow when diverting the pressure.:confused:

[arjunior45]

I really do not know what to tell.

All I can see from the removed oem valve is that the 'membrane' in this valve blocks the way at tube - hose 'A' at the first picture attached {JimNielsen's picture}.

The same hose is blocked by the cylinder in my 'new' adjustable b-o valve and this hose is the one that goes to the one that connects the intercooler with the intake manifold.

[Juan AR155Q4]

Blow by and see wich one is blocked.
A should be blocked.

[arjunior45]

on the oem one I removed, 'A' tube {to the air filter} is blocked with a piece of round plastic part.
Tube 'B' is free of anything that can block communication with the other tube
I believe there must be a membrane and probably a spring too at the small bore tube.

As soon is possible, I'll cut the plastic case to see how is made.

[jimnielsen]

here is a picture of the valve in its 'natural habitat' - can we see a picture of your new valve, Nick?.. I have to get one as well as I don't think I am going to use this style of valve when I put the car back together..

jimn~

[arjunior45]

thanks for the picture Jim.
My oem one was mounted in this way but it's a little bit strange.
I'll try to explain what I mean.

The membrane {more like a solid round piece of plastic, with a kind of o-ring} that blocks the communication between tubes 'A' and 'B' is located at tube 'A' - the one connected to 'air filter' in your 'normal habitat' picture!
Also there must be a real membrane or even a spring just under the small bore hose that keeps this 'solid piece of plastic' in the close position, not letting any communication between tubes 'A' and 'B'.

So as boost increases, 'pressurized air' {from the aircooler - tube 'B'} push this membrane to stay close! So does the positive pressure at 'small bore' hose, pushing to close position of the membrane, as boost in the inlet manifold increase. But what happens when the throttle is released - closed?

As far as I can imagine, this accommodation of the oem b-o {stall prevention} valve, in order to let open this ?solid round piece of plastic? {at tube ?A?}, assuming that when throttle is released the turbine keeps spinning by inertia pressurizing the air in tube 'B' and trying to keep the membrane in close position,
- the vacuum in the small bore hose must be quite big!
Big enough to overpass:
1} the air pressure given by the turbine {which should keep spinning by inertia} in tube ?B?
and
2} the pressure ? force by the ?membrane ? spring? at the small bore hose!
That?s what is a little strange for me!!!

This kind of behavior {if I?m not mistaking} of the ?oem? b-o valve can easily explain why I had the engine keep revving for a while after having released the gas pedal! The oem valve {or more like the engine} after closing the throttle, needs some time to ?build? the necessary vacuum at the small bore tube to overpass ?1? and ?2?!

What happens to the boost in the manifold? I do not know and never cross my mind to measure the boost at various situations, mostly what happen when gas pedal is released! Shame on me!
The only benefit I can imagine is that with the oem accommodation of the b-o valve, there must be left some amount of air pressure - boost at the throttle valve {when throttle is closed} keeping engine revving for 1 ? 2 seconds at high rpm. This might have a positive impact at boost pressure during gear changes. But not so sure! I?m only guessing.
The only thing I?m sure of is that with the oem b-o valve, after releasing the gas pedal the engine kept revving at higher rpm than it should have! And this was ? is quite annoying for me!
That?s all I?m sure of!

[arjunior45]

here is a picture of the valve in its 'natural habitat' - can we see a picture of your new valve, Nick?.. I have to get one as well as I don't think I am going to use this style of valve when I put the car back together..

jimn~

Jim I'll try to find the picture of it as it was a replacement of the oem valve.
Not too different from the oem one. It just has a metal piston that blocks tube 'A' and a spring placed between the piston and the surface where the small bore tube goes. I can turn left or right the part where the small bore hose goes increasing or decreasing the force of the spring that keeps the piston in 'close position'. They have told me that this way, this valve can be adjustable from 8 psi to 16 psi. What does this mean in practical terms I can't say for sure right now!

Need to settle down the problem with my idle speed before I can have some certain comments to make for this valve.

So far I can tell you that I have connected this valve having :
1} tube 'A' {that has the piston} connected to the 'intercooler's tube'
2} tube 'B' to free air for now {so I can hear it when blows off}. When everything will be finished I'll connect this tube to the 'air filter'}.
and
3} 'adjust' it to 12 psi. This is not the final adjustment as I was told to tighten the spring so much that at idle speed does not allow any air to 'blow off'. I'll try to do it in the next few days, maybe this weekend, and then I'll go for some tests on the street.

My first comments are:
1} above 4000 rpm, I can hear this valve blow off every time I cut the gas {closing the throttle} and becomes quite sensitive to throttle movements at higher rpm {6500}.
Bellow 4000 rpm I was not able to hear it blow as it was quite loud outside.
2} at 6500 rpm, even a small release of the gas pedal leads to the 'PSSSSSSS' sound {that I do not like that much}
3} In general, I believe that I have faster response to gas pedal movements {either giving gas or cutting gas} and certainly does not need those 1 - 2 seconds to start cutting revs when throttle is closed.

Did not take the car for a ride as my wife had to go to work, so I can not say if there is any difference in the street 'behavior'. But I will this weekend, I hope.

[arjunior45]

The arrows on that diagram do not seem right to demonstrate air flow when diverting the pressure.:confused:

according to Jim's picture the way the air flows is the one at the picture from the manual!!!
I'm confused too.
I believe in this way there should be quite a vacuum at the inlet manifold before the pressurized air is converted to the 'air filter'. That means that 'pressurized' air will slow down the turbine movement - spinning quite a lot before converted to the 'air filter'!!!

Is there something missing???????

[arjunior45]

@JimNielsen

See ebay item number : 120414525884 Sorry can not make the link to this work - do not know why.

this is like the one I've bought a year ago {from a US manufacture - can't find his address any more}. The only difference from the one on ebay right now is that the one I have has the tube to the air filter exactly like the one for the 'intercooler'. So, I can have it as an 'oem' valve, sending the air back to the 'air filter' hose or I can just remove the 'middle' part {unscrew it} and have the pressurized air diverted to the atmosphere.

I modify the picture from this ebay item to show you how it is. I need to remove mine from the car to have a dissent picture of it. Hope this 'mod' picture can help you a little.