Blow Off Valves / BOV for the turbo noobs like me :O

[matchtheclown]

Hey,
I should probably just hit up howthingswork.com but I want some suggestions too!

AFAIK
The boost controller controls the pressure going into engine from the turbo's.
The BOV just vents the excess pressure which is there when you are off the / between gears as the engine is not accellearing and wont be taking the pressure created by the turbo's right?

Assumed:
You need to set the BOV psi higher than the boost controller because if you have the boost controller set at 12psi and the bov set to vent at 10 you will lose boost.

Also assumed:
BOV's are really just for the vent noise? The factory ones have been known to leak.. or is that the factory boost controller? Gah looks lost

Now are all bov's manually set? I have have NFI to be honest... :redface:

I am looking for a decent one which will work with my tubrotech MBC and isn't to expensive.

Thanks guys.

 

[Guest]

you lost me at AF AIK

i didn't know you had to set bovs to any psi thought they just vented pressure no mater how much.........

also whilst im sounding rather dumb what happens when you make your bov plumb back? wouldn't it just be the same as not having one at all?

 

[matchtheclown]

AFAIK > As Far As I know,

Let's walk around in the dark a little more.

I'm pretty sure the point of the Bov is to vent the back pressure which can damage the turbo's otherwise. The plumb pack vents it into your exhaust so it still get's rid of the pressure.

 

[Guest]

BOV's release the pressure that is created between the turbo and the throttle body upon closing the throttle.

this stops the air trying to escape back past the turbo, though the intake system, and causing compressor surge/flutter/whatever you want to call it.

most aftermarket BOV's are adjustable, but you dont really set a certain psi, you can just tighten/loosen the spring that holds the piston in place.

the tighter you set it, obviously more boost pressure it can hold, but over-tightening it can cause it to not open as much, or not open at all, negating the whole reason it is there...

a plumb-back BOV simply returns the built up pressure back into the intake system BEFORE the turbo, whereas an atmospheric BOV will vent it externally.

atmospheric BOV's can cause a few issues, firstly if the car is AFM based, like ours, it can cause stalling, as the ECU expects a certain amount of air to be in the intake system, and adds fuel accordingly. having less air and more fuel causes it to run very rich, and it can also cause stalling issues.

also, as they vent to the atmosphere, it can be illegal as all gases vented from the engine are supposed to be passed though the exhaust/catalytic converter system.

 

[mookers]

So when they leak it means they lose pressure under open throttle, thus decreasing your boost?

 

[Guest]

yep.

like any springs, they will weaken over time

 

[Kenneth]

BOVs work on pressure change.

When the pressure is equal, the BOV is closed. This is because the pressure on both sides of the BOV is equal, so the piston or whatever it is does not move.

When your foot is on the accelerator and the throttle plate is wide open, the pressure in the intake plenum is close to the pressure in the pipe work, because of this the BOV doesn't require a lot of spring pressure to keep it closed.

Because things are not ideal, there is pressure drop (and in plumb-back there will be suction on the outlet) between the plenum and the pipe where the BOV is. (most of it probably created by the throttle body)

If this pressure difference is greater than the spring pressure which is keeping the BOV closed, then the BOV opens, even at full throttle.
The more air you are trying to flow through the throttle body, the greater the pressure drop and the more likely the BOV is to open. Standard BOV has a very weak spring and opens very easily.

When at idle, the pressure in the plenum is much lower than that in the pipe work, and so the BOV wants to open.
In plumb-back, this isn't a problem, in fact it is good because it means that the air does not have to flow past the turbo compressor to get to the throttle body. As such, the standard BOV has a very weak spring pressure.

 

[mookers]

Need a diagram!

 

[Kenneth]

When you go from throttle open to throttle closed, the plenum pressure drops very quickly and goes very low. As the turbos are still pumping air, the pressure in the pipe work increases (can spike quite high).

At this point the low pressure in the plenum is trying to pull the BOV open from one side. At the same time, the high boost pressure in the pipe work is trying to push it open from the other.

The resulting pressure difference is very high across the BOV and it opens, venting the excess pressure in the pipes.

Ideally, a VTA BOV should have the spring pre-load set so that in deceleration, the BOV is almost open when there is no pressure in the pipe work. In this situation any positive pressure in the pipe work causes the BOV to open and vent the pressure, then as soon as the pipe work pressure equalises, the BOV closes to prevent sucking in un-filtered air (and in our case, un-metered air that has not gone passed the MAF)

 

[mookers]

Still need a diagram lol

so much easier when you can see the components and the airflow path...

 

[matchtheclown]

Hmm..... so basically an after market box wont leak as much as the stock one which makes things shit.

I think that's about as much as I need to know.... I don't really understand it all yet but i'm sure i'll get me head around it.

Any reccomendations on which one to get?

 

[gorgath]

Either SARD R2D2 or HKS SSQV

Have a read on this thread and you'll find your answers.

 

[frozen]

you can use any bov you like in my opinion, i just use a Greddy Type RS (its just a REALLY simple bov, with very simple design. full venting) and i have no problems at all. The car feels like it runs better when there is some air recirculating though.

 

[Kenneth]

One thing I have noticed is that with all the VR-4s I have had running VTA, the pipe work does not build up oil deposits.

 

[matchtheclown]

Cheers gorgath I searched for BOV not BOVs when I did

So what do you recon about this one:
http://cgi.ebay.com.au/Brand-New-HKS-Style-2008-latest-model-SSQV-BOV-34mm-kit_W0QQitemZ180303028225QQcmdZViewItem?hash=item180303028225&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A2|39%3A1|240%3A1318

It's probably a copy of the HKS, so maybe not a good idea? It is advertised as ridaculously loud however which I don't think I'm after....

I really just want a decent one which works for less than $150 delivered :/

Here is a rippoff Greddy one for $130.
http://cgi.ebay.com.au/Brand-New-GREDDY-TRUST-TYPE-RS-style-BOV-34mm-kit_W0QQitemZ180303633847QQcmdZViewItem?hash=item180303633847&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A1|39%3A1|240%3A1318

What do you say? Clones are ok?

 

[Guest]

A decent one for $150, the only real option that I can see is the BOV from the Evo 8MR/IX, exact same design as ours but has a metal construction. The current exchange rates issues have put it around the $200 mark though, there is a bloke on EvoOZ (JASRacing i think) that sells them, or get in contact with SiliconAngel on here as I think he was going to do a Group Buy on them, but other commitments have gotten in the way.

Otherwise don't expect to pay any less than $300 for a genuine Greddy or HKS.

 

[Guest]

atmospheric BOV's can cause a few issues, firstly if the car is AFM based, like ours, it can cause stalling, as the ECU expects a certain amount of air to be in the intake system, and adds fuel accordingly. having less air and more fuel causes it to run very rich, and it can also cause stalling issues.

also, as they vent to the atmosphere, it can be illegal as all gases vented from the engine are supposed to be passed though the exhaust/catalytic converter system.

so a plumb back bov would be the better way to go for our cars then?

 

[gorgath]

I got geniune SARD R2D2 and paid around $260.

 

[frozen]

definately plumb back is better, i got the plumb back kit for mine and the car seriously drives smoother, alot smoother, however the sound of vta makes my girlfriend happier... (no shes not one of 'those' girls, but she prefers some sound to no sound)

I paid a rediculous $350 or $400 for my genuine Type RS. Main reason is i like the slight surge before the vent, as in they have an adjustable spring tension, meaning it will only open when there is enough boost/vaccuum as explained rather than opening at any boost level like an ssqv. When i have all the piping and everything sorted i hope to get some mild flutter before the pshhh which is a nice sound, even though somewhat bad for the turbos.

Anything on ebay that has the word "style" is a fake. eg. HKS style or Greddy Type RS style.

 

[Mrk_VR4]

I've got a Evo 8 GFB Stealth FX BOV and it is really nice to use, and has caused no problems. Its a hybrid BOV allowing you to vent some air to atmosphere and recirculate some air back into the system, avoiding any issues caused by the MAF and the loss of air due to VTA. The amount of air being vented or recirculated is fully adjustable (0-100%) and because of its design the boost level at which it beings to VTA can be varied by adjusting the spring force. So unlike other VTA BOV's, such as the HKS SSQV, it doesn't VTA at every gear change, only when your giving it enough to build up enough pressure. It is a little on the pricey side though with an RRP of ~$530, i got mine at a stock clearance sale for $350 though.