eggy790

iTrader: (20)

Hi

Ive read a lot about Dump Valves and BOVs being crap and a waste and its best to standard as they leak or dont do what the standard one does.

Seriously has no one invented a BOV that can do the exact same as the standard one? or better?

ive seen loads of expensive ones with a number of different ports and recircs etc. are they all really the same i.e. crap?

Hope someone can just clear it up

Cheers

Peanuts

iTrader: (15)

you are getting slightly confused in terminology I think.
BOVs are thought of generally as VTAs that Vent To Atmosphere.
Here in lies the problem with metered air being ejected from the system.

There are plenty of recirculating dump valves and I am sure some of them will do the same job, ie Forge seems to have a quality name.

The standard dump valve works perfectly, so how do you propose to better it?

eggy790

iTrader: (20)

thanks for yor answer

nicely put

i suppose your right, would they be any that you recommend then? as i dont see anyone recommending them..

Peanuts

iTrader: (15)

I recommend the standard one.
It's great and does what it says on the tin.

Wurzel

iTrader: (1)

I had a GFB VTA dumpvalve and had to bin it once I got to about 330ps because it was leeking like a sieve and was causing the transmission to shake violently. I swapped for the plastic subaru one from an MY97/98 car and all my problems vanished with the old DV.

StickyMicky

i have a TAS (unsure if they even still exist?) uprated piston recirc valve that i bought years ago.

you dont get any of the gay noises and stuff, and can set the dump pressure to what ever you want (i modified mine to hold a LOT more pressure)

the only reason i changed my 97 recirc stock one is that it started leaking and doing the ":moo" on boost (if you have a 97-98 you will probably know what i am on about)

the stupid, noisy, gay, chav-horn ones are usually the first ones to go **** up.


best thing i ever heard about the stupid gay ones, came from a local bloke who said he needed one because he had 1.5bar and 400bhp

completely clueless springs to mind

he is on this forum as well

Rossco_

iTrader: (1)

Yeh man, look in the forge website, they do an exact replica of the standard subaru one but in better materials (i hope) seems a fair price too

eggy790

iTrader: (20)

link?

ditchmyster

iTrader: (7)

thread hijack , so if i have a vta and fit a recirculating, is there anything else that needs to be done? hypatheticly speaking of course

joz8968

iTrader: (13)

I have the Forge one as shown in this link (ony 20 sovs from another member)... Forge Motorsport | Alloy Fabrication. It's for the early 92-96 v.1/2 cars. As you can see it's exactly the same pattern, but is made of metal, so wont split, like the OEM plastic one could. Also, it's bound to have a more robust diaphragm inside (or maybe a spring ).

Forge also do the MY97/98 v.3/4 one - like this http://i169.photobucket.com/albums/u.../EVORECIRC.jpg - where it's the same... Apart, that is, from the entry being at the bottom i.e. opposing the small manifold port.

rob73

intresting thread....what boost can the standard denso re-circ handle before it gives up?

silent running

Any amount.

rob73

cool,i was under the impression that these became unpredictable after 1.5 bar thanks for that tho.

Northy 7

My BOV makes a ssshhhhhhhhhhhh noise when excelerating before making the swooosh noise when I lift off the excelerater is this the norm or is it leaking like you say?

joz8968

iTrader: (13)

As SR said, theoretically any amount...

When there's positive boost in the inlet manifold, the pressure on both sides of the dv's diaphragm, or spring, is exactly the same, canceling each other out, therefore remaining in situ i.e. shut (so you can see by this that it doesn't matter how much boost there is). However, a soon as the boost is released i.e. coming off the throttle and shutting the throttle butterfly off from the inlet manifold, then the air pressure rapidly heads back through the TMIC and towards the dv entry. So now you've got positive pressure acting on the underside of the diaphragm/spring, whilst there's a vacuum acting on the top (no positive pressure in inlet). This causes the diaphragm to raise upwards (the double whammy of positive pressure pushing whilst vacuum pulling), thus opening the valve and forcing the air back into the air intake system to be, as the name suggests, recirculated.

silent running

Well perhaps I should expand on that; there will be a point at which the thing will blow apart. But basically on the inlet side of it, you've got a whacking great spring holding the plunger shut which is also fed boost/vacuum from the back. So under boost conditions, you've got boost on the inlet side, boost plus a big spring on the other, the thing stays shut, there's nothing else it can do. Soon as you let off, you've got boost on the inlet side but vacuum on the back of it, it pops open and dumps boost through until pressure equalises again.

So what I'm trying to say is, there is no 'boost limit' as such in normal use. It either works or it doesn't. When you see dump valves such as Forge which recommend different springs for different levels of boost, this simply tailors the opening/closing response to suit varying target boost levels. It doesn't alter the boost capacity of the valve. A dump valve will always stay shut under full boost unless it's really really flimsy and blows apart.

Part throttle conditions are when you get problems with aftermarket dump valves.