The air the re-circ vents back to the intake pipe is post maf, the maf has already seen that air once so the ecu calculates the correct amount of fuel. The ecu knows that the re-circ will send that air back to intake. It's the fact the ecu knows that air will be used again. !!!

It's a fairly good video.

People will still go for a DV for the sound though. Let them do it, just don't buy their cars off them. I'm fed up of explaining it to people now.

Still don't get it. :norty:

And that pressurised air on lift off, does it serve any other purpose?

TAF again!

Not being funny, but that doesn't make sense. ? Explain what you mean.

Matt is the chap who claims to hear turbos spooling on other cars from 50 yards away :lol1:

He's either a WUM or doesn't know the square root of FA :thumb:

WTF is a wum ?

I heard the Banana spool from 400 yards away. I could hear chatter too and he wasn't even moving.

You all seem to have leaked a little bit of Scoob knowledge over Yuletide.

To quote my new favourite film 'Born to Race.' "It's one thing to understand how to bolt aftermarket parts to your car. It's another thing entirely to understand how they all work together."

How does a dump valve work ?

A blow-off valve is an air pressure bypass valve that is placed between the turbo compressor and the throttle.

When your turbocharged car is on boost, the entire intake system is filled with pressurised air; from the turbo compressor, through the throttle body and inlet manifold and into the combustion chambers. When the throttle is closed, this pressured air can no longer enter the engine. The only path available for the air is to try to flow back the way it came, through the turbo compressor the wrong way. This creates a fluttering noise on the blades of the still-spinning turbo compressor.

In addition to making this fluttering noise, a noise that is probably unwanted in a nice new turbo car (though actually extremely popular amongst modified-car enthusiasts!) it is often claimed that the load placed on the turbocharger from this pressurised air flowing through it the wrong way can cause premature wear or damage. The jury is still out on this, as it's quite difficult to directly attribute a turbo failure to not having a blow-off valve fitted, however high boost levels without a Dump Valve are definitely not going to help turbo life,

There are many other reasons car manufacturers fit blow-off valves to their cars, mainly to do with emissions, fuel economy and drivability. In aftermarket applications though, the main reasons for fitting a Dump Valve are to hold higher-than-standard boost levels, to give better throttle response (than a factory Dump Valve) by staying closed whenever it's not venting, and of course to make noise!

A blow-off valve (also called a compressor bypass valve or diverter valve) is a valve, generally a piston type, which is placed between the turbo compressor and the throttle to bypass the pressurised air on a closed throttle, either plumbing it back into the turbo inlet for silent operation, or to the atmosphere to make the signature blow-off valve whoosh.

How a blow off valve works

A blow-off valve is vacuum/pressure actuated piston-type valve. It uses vacuum/pressure signals to tell the piston when to open and close.

At idle there is engine vacuum on the top of the Dump Valve piston trying to suck it open, and no vacuum or pressure on the bottom of the piston. Since a vent-to-atmosphere Dump Valve needs to be shut at idle to avoid air being drawn in through it, there is a spring inside a Dump Valve with the job of holding the piston closed. The spring preload adjustment is to allow for differences in engine vacuum from car to car, and variations in atmospheric pressure at different elevations.

On airflow metered cars the air drawn in through an open vent-to-atmosphere Dump Valve at idle would confuse the ECU and cause over-fuelling and stalling and in any case, the air drawn in is unfiltered.

Under cruise conditions (off boost) the Dump Valve is experiencing similar conditions to when the car is at idle, but there is less vacuum present on top of the piston because the throttle is partly open. If the Dump Valve spring has been adjusted to keep the piston closed at idle, it will also be closed at cruise.

On boost there is boost pressure on both top and bottom of the Dump Valve, the forces from which counteract each other, so the Dump Valve remains closed.

Immediately after the throttle is closed under boost there is vacuum on the top of the piston and boost pressure on the bottom of the piston, which together, quickly open the Dump Valve to release the pressure. When the pressure has been released, the Dump Valve closes.

Edited for RS TAF to understand.

I hope you arnt actually referring to myself, I have a BA HONS degree in motor engineering. And have worked with performance cars / subarus for the past 14 years. What information exactly are you trying to obtain ?

200,000 sperms and you were the quickest, it dosen't say much for your tadpole brothers and sisters that's all I'm saying.

Tell me you copy and pasted that, if not that's an excellent post mate. Ref post 41

Amen.

Take your head and bang it against a wall, he has had it spelled out to him in black and white in the other thread and it still isn't sinking in with him.

Hahahaha. That actually made me lol !!

Other thread came to a logical conclusion, it's the sheep and experts in here who are quoting shine from a time VTA's opened when they felt like it.

He's the funniest Cuck on SN.

Still TAF!

I have a HND in Design, Photography/Art & Design qualifications and I've worked for 2 Glossy magazines designing pages, ads and contributing illustrations. I still only understand art in all it's guises and different mediums around 25%. That said I can draw a Subaru better than you can fix one and that is a fact.

I've obtained most info already from 1 clued up member, jury is still out on what causes rich running on a 2001> DV Delete set up.

And yes I know what Dump Valve is before you try and get high fives from the onlooking Sticker hating clique.

OZ RACING
Goodridge
Brains
Alpine
Sparco
Lancer VI RS

...Fully the shopping list on your car door.

Well why don't you explain to us uneducated mortals. ???

Firstly your friend means I'm FAF!

Secondly, I've read a Blanked off DV, delete if you will, will cause rich/rough running, one theory is that a bit of compressed air makes it to the MAF before it depressurises or gets re-used and tells the mother futcher to throw a bit of fuel in.

But the common sense of a door handle!

No, I mean TAF!

I've never been fashionable tbh.

Mate tell you buddy to hurry up on the phone to Japan. I wanna buy this plate and go to sleep.

I understand what the theory is your getting at. But have you actually dismantled a maf ? The maf sensor is basically a heated resistor. It cools as air travels past it, the element is encased in a shroud. So air which is back tracked up past the maf shouldn't have any effect as the element won't see the air. Just like if the wind was blowing and you were stood in a bus shelter !
Also don't forget, even when the throttle plate is fully closed air will still make it's way into the combustion chamber. Via the icv.

TAF = Thick As ****.

Nite nite :D.

Lol, we all waited all night for the answer.

I thought you meant 'tough as,' seeing how I won't back down to the VTA hating crowd.

I have taken one apart and I know what it does except for the IAT feature which measures ambient air temp? I heard it may be this feature of the MAF that might account for the over-fuel on a DV delete lift-off...

This was one of my first theories on what actually cause a brief rich spell after lifting off the gas. I presumed on a re-circ slightly pressurised air gets forced into the cylinders and on a VTA the pressure can't match what the ECU expected.

The theory, aided by the very understanding and patient joshnosh, then turned to pressurised air stopping fresh air entering past the MAF via the airbox, on a VTA system there would be no block or equalisation of pressure ergo the vacuum effect of the Turbo draws in some air past the MAF that does not get used and it's this cheeky bit of air that kids the ECU into thinking the throttle is still open a tad.

A similar principle to what everyone quotes but kinda after the fact so to speak.

I still have many unanswered questions though, things like does increased boost pressure = increased over-fuel? Why do some car owners claim a VTA makes their car run crappy at other times such as tick-over and casual off boost cruising.