BOV Spring

[caspernicus]

Re: BOV Spring

Looks are about the only thing that seperate manual boost
controllers. Mine was tucked out of the way, so I didn't care.

[ssms5411]

Re: BOV Spring

Yeah , I saw posts how to make one and the ones on ebay but really didn't like them, as along as it will get me to my to my 10-12 PSI without me having to swap my bigger wasgate spring in I'll be happy.

[Kilted]

Re: BOV Spring

Sorry about that I got the 2 mixed up again since I had just changed out my Tial 38mm wastegate spring. I bought the Tial 50mm version 2 BOV with 10 PSI spring. I haven't looked into mine just so it holds at 10 PSI at least. I had a XS bov serious which I had to use spacers to dial it in, when I ran my powerdyne.

How much boost are you running? I'm not sure what factors determine what blow off pressure I should be aiming for.

I honestly don't understand why you'd want the vacuum to get very high before the BOV releases your boost pressure.

Doesn't the turbo start slowing down as soon as you let off the gas and the throttle plate closes?
So why would you want the BOV to wait until 10 or 11 psi (all the while your foot is off the gas) before it finally did it's job and let the boost go somewhere so the turbo could keep up it's RPMs?

For instance, why shouldn't the BOV open as soon as vacuum is present so the turbo could continue spinning as fast as possible, blowing it's boost into the atmosphere in anticipation of the throttle plate opening again?

I'm not thinking about trying it, but I'm just curious about the physics of that one. I'm sure there is a reason for it whether I can figure it out or not.

[caspernicus]

Re: BOV Spring

So why would you want the BOV to wait until 10 or 11 psi (all the while your foot is off the gas) before it finally did it's job and let the boost go somewhere so the turbo could keep up it's RPMs?

That psi rating is negative, which is vacuum.
The bov stays closed until the pressure difference between the charge pipe,
and the intake manifold equals your spring pressure, then it opens.

Don't over think this. The bov's job is to relieve the pressure in the pipes so
it doesn't go back through the compressor inlet.

[v6mOtOrhEAdftOp]

Re: BOV Spring

dumb person's terms, the BOV prevents compressor surge or "flutter"

[Kilted]

Re: BOV Spring

Yeah, it prevents surge, but not all of it. For it to prevent all surge, It would need to have a weak spring that would allow it to open as soon as vacuum was present. Then there would be no surge against the turbo at all.

I think I figured out why you'd want a delay though. It keeps some pressure ready for when you get done shifting. If you've taken your foot off the gas, then you aren't making boost, so the spring in the BOV causes it to keep a little pressure to get things going again as soon as the throttle plate opens. That would cause your turbo to spin up more quickly after each shift.

I have to know why things are they way they are. I can't help it.

So far no one has been able to tell me how they learned what BOV spring weight to use by the way.

[Blizzard242]

Re: BOV Spring

I have to know why things are they way they are. I can't help it.

So far no one has been able to tell me how they learned what BOV spring weight to use by the way.

I can totally relate with you there.

I never learned. about the BOV spring and all that. Honestly, I shimmed my spring and listened to my turbo. I'm probably doing something wrong. But eh.

[caspernicus]

Re: BOV Spring

I think I figured out why you'd want a delay though. It keeps some pressure ready for when you get done shifting. If you've taken your foot off the gas, then you aren't making boost, so the spring in the BOV causes it to keep a little pressure to get things going again as soon as the throttle plate opens. That would cause your turbo to spin up more quickly after each shift.

I have to know why things are they way they are. I can't help it.

So far no one has been able to tell me how they learned what BOV spring weight to use by the way.

You don't want a delay. When the throttle blade closes, the pressure is going
to go somewhere. It's not going to chill in the pipes and wait for the throttle
blade to open again. It's either going out the bov, or back through the
compressor cover.

You need to find out how much vacuum the motor pulls at idle, and then
select the corresponding spring.

[Kilted]

Re: BOV Spring

But if you have a spring in your BOV keeping it closed, then isn't at least some boost forced to go back through the compressor cover while the vacuum pressure builds to the point where it can overcome the spring?

What if the spring was (for the sake of argument) a 50 pound spring. Obviously the BOV would be useless because it wouldn't open. All the boost pressure would be forced to go back through the turbo as if you didn't have a BOV.

That said, how could there be no delay at all if the spring was 11 pounds?

Is there vacuum while you're accelerating until you begin to create boost, and the BOV has a certain size spring to keep it from opening while you're accelerating?
That's got to be it. Right?

[caspernicus]

Re: BOV Spring

Is there vacuum while you're accelerating until you begin to create boost, and the BOV has a certain size spring to keep it from opening while you're accelerating?
That's got to be it. Right?

Your motor pulls a vacuum until the turbo does it's thing. N/a cars are always
in vacuum except for WOT where they hit ~0 vac.

I'm out of town right now, but when I get back in a couple of days I'll take a
video of my boost gauge with me driving normally. Maybe that'll clear it up
some more.