boost controller for BOV? why not?

[gnailuh]

ok, still trying to get all of this around my head. why is there only boost controllers for the wastegate? if the 2G bov is bad and leak air to low psi, why not stick a boost controller (manual one) on that side of it too? shouldn't the concept be the same?

i'm i stupid? there's gotta be something i'm not seeing... please school me.

 

[InferiorWang]

you want the bov to be able to open whenever the throttle plate closes no matter what the pressure is as long as there is positive pressure and not vacuum. A "boost controller" style device would hinder this.

 

[gnailuh]

ok, what you say makes sense in some sense... if it opens on any pressure (as long as not vaccum), then why does this business of leaking come into play? why do people make such remarks as "the 2G bov leaks at 14psi...".

i'm still missing something i think...

 

[DSMeclipse4G63]

Ok what a boost controller does is make it so more pressure is needed to get to the wastegate to control boost. if you used one on a bov hardley any boost would get to the bov (unless it was turned all the way down). so during boost your bov wouldnt be pushed down by boost pressure and would leak worse. under vacuum the bov wouldnt open so your turbo would sure and wouldnt open at all. Thats why hope that helps.
Andrew

 

[Colossus]

The boost controller only allows the turbo to create a certain amount of pressure. The BOV allows this pressure to vent. The BOV only vents upon shifts, neutral, etc. More or less whenever you let off the throttle.

But, if you're building say, 19 psi. You get your boost controller set to 19 psi, therefore the turbo will only put out a max of 19 psi. The BOV will then see this 19 psi of pressure. This is ok. Now, crank it up to 25 psi. The turbo puts it out, boost controller stops it at 25, etc. But, if the BOV only will hold say 24 psi of pressure before it leaks, you're leaking 1 psi of pressure. It'll still build boost, but at so much pressure, air leaks out just a bit.

The BOV's job is to relieve this pressure only upon shifts, so that there isnt a back surge of air going towards the turbo, and vacuum is made again.

Another example would be holding your fists around an air compressor hose, and then blowing air into your hands. Your hands can only hold so much psi before air begins to leak out of them. You don't want air leaking while pressure it being created, or you lose the pressure, and power.

 

[gnailuh]

I found this article:

"In the CBV case, pressurised air is returned to the turbo compressor inlet for reuse, instead of being dumped to atmosphere. The bypass valve is <B>open</B> under normal low-load engine running conditions, and closes firmly when positive (boost) pressure is present in the inlet manifold (or plenum chamber). When on-boost and changing gear (throttle lift-off), a sudden lower pressure condition is created in the manifold and the valve is pulled open again, directing pressurised air back to the turbo inlet."

The fact that the valve is "OPEN" was what I was looking for... that cleared it all up... using pressure to "CLOSE" it.

But (if you stick with me here), shouldn't MORE pressure close it even tighter? Why would it leak with more pressure? So is that when the plastic nature of the 2G BOV comes into play? Since it's plastic, at high pressures the shit don't seal well and leaks?

 

[TurBoGs-T]

I'm gonna give this a shot.......

The Bov is Only meant to open once the throttle plate is shut, to redirect the air back into the intake. Thus allowint the turbo to stay spooled. But when you have the throttle open you want the BOV to be able to let all the air pass thru without it leaking out. The stock 2g bov isn't strong enough to stay shut when you throw 14+ PSI at it. Sure it does it's job blowing off but it need to stay shut during boost.

The wastegate is there to provide an alternate route for air to go once your turbo is producing your desired amount of boost. That's where the Boost controller comes into play. The boost controller basically hold's back the pressure from the wastegate until you hit your desired amount of boost then it let's it go, and the wastegate opens.

So in essence we don't really want the Bov to open at a certain PSI, we just want it to open once the throttle plate shuts. So there's no other solution to a leaky Bov except get a stronger one.
HTH

 

[gnailuh]

ok, don't get me wrong here... i REALLY appreciate everyone answering... but i now understand what the bov is suppose to do, however, no one's really answer the heart of the question, what makes the 2G bov bad? i know it's bad because it can't hold pressure, but that's counter intuitive to how the bov functions. explain the physics and mechanics please...

now, if the bov is "open" by nature, and it uses the pressure to keep it closed, so whenever a lose in pressure (vacuum i guess) is detected, it essentially opens up again and vents out the air (or recircuates the air). by this line of reasoning (so correct me if i'm wrong here), wouldn't "MORE" pressure cause it to seal "MORE" tightly?

to me, it looks like the wastegate and the bov works almost in opposites. so is it because the plastic nature of the 2G bov what causes it to NOT seal well when high pressure is present?

 

[DSMeclipse4G63]

The stock 2g bov has a terrible spring rate...you can push the bov open with your fingers VERY easilly as compared to after market or a 1g bov. The fact that it has a crappy spring and the fact that at 15 psi it opens the spring and leaks boost back to the intake and that 15psi cant even help the stock bov shut and seal at anything over 11 psi. buy a 1g or after market to fix it.
Andrew

ps the vacuum line uses vacuum to open the valve on decel and closed throttle and boost helps push the valve closed on accel to keep it sealed.

 

[TurBoGs-T]

Alright let's start off by not relating the two. The wastegate and the BOV are completely different, and work different. You seem to be comparing one to the other. We can't do that.

The Blow off Valve "IS NOT" naturally open. It's shut. The aftermarket BOV's have screws, washers and springs to keep them closed. And by tightning the screw or adding washers it makes it harder to open.(making it able to hold against more pressure) The bov is opened by the extreme pressure build up in the pipes when the throttle plate shuts. But the vaccum does assist in opening it,as the pressure does keeping it shut. I think that you are thinking that the bov is solely operated by the press/vac. it's not. It's the screws and springs used to make it tighter. That's why you hear people crushing their 1g bov's to hold more boost. Crushing it makes it tighter. it's not the fact that it's plastic that it can't seal it's the fact that there is no way to make it tighter to handle more boost. They didn't make the 2g bov with any intentions of having it hold more than stock boost.

WHEW......................

 

[kpt4321]

If the BOV was as simple as you guys are making it out to be, then it would never leak under boost. The pressuere from the intake manifold on top of the BOV, coupled with the spring pressure, would hold it shut until manifold vacuum was achieved.

However, you're missing a crucial part. The BOV has a quick-release port, which basically blows pressurized air under the seat to help it lift quickly. Without this, you would get terrible compressor surge because the valve wouldn't be able to lift off the seat fast enough.

It's this port that adds to the leaking under boost; You can isoltae it, but like I said then you will get nasty compressor surge. As such, you can rig up some kind of switch that alows you to open and close this depending on the throttle position. I have done quite a bit of experimentation with this, from running a WOT switch, to running a boost activated switch.

Check this out:

http://www.gusmahon.org/html/Talon BOV.htm

 

[gnailuh]

Now these are the type of responses I'm looking for!!!

But again, I really appreciate everyone for putting up with my dumbness... it will all come clear to me soon... I hope.