BOV and WG psi question

[Kwando]

When I bought the tial wastegate and bov I opted for the 7psi springs in each. But I only plan on running 5psi. would I need to get new springs? The lowest tial spring is 7psi… :confused:

Is the pressure loss seen in the IC and charge pipe noticeable?

[HONDA GHANDI]

there is a 5.8 psi spring and a 4.2

[Enthalpy]

Is the pressure loss seen in the IC and charge pipe noticeable?
It depends on the intercooler and how much air you are trying to ram through it. Just like any source of restriction, the more air you try to ram through it, the larger the pressure drop across it becomes. This applies to sub-choked flow, which is a valid assumption for intercoolers and charge pipes. It is not for turbines.

[Kwando]

the lowest BOV springs i can find are 7.

[sbiggi]

the lowest BOV springs i can find are 7.

The bov spring has absolutley nothing to do with the amount of boost you are running.

You select a bov spring based on how much vacumm you pull at idle. There is a guide on tials site.

[Kwando]

i'm a n00b. good thing i'm not doing the install. :rofl:

[sbiggi]

i'm a n00b. good thing i'm not doing the install. :rofl:

I was sold the wrong spring when I got my Tial because the nobody told me different.

I only pull 11inhg at idle, so I run a 7psi spring and I shimmed it with 1 washer. Originally they gave my a 11 lb spring and my car could hardly open the bov even after full boost.

[HONDA GHANDI]

Oh, sorry. Thought you were talking about WG springs. Yes, the WG spring wont affect your boost levels, but will need to be adjusted to open faster.

[Kwando]

tobi i'm going to order a .4bar WG spring... but i still don't understand why the BOV doesn't go below 7psi. So if i am only running 5 psi, basically the BOV will never open. If that is the case, why do i need a BOV?

[Enthalpy]

tobi i'm going to order a .4bar WG spring... but i still don't understand why the BOV doesn't go below 7psi. So if i am only running 5 psi, basically the BOV will never open. If that is the case, why do i need a BOV?
The BOV will open at idle. The typical engine idles at 18"-ish at this altitude with stock cams. Your spring therefore has to overcome this plus 1-2" positive pressure coming out of the turbo, even at idle. You only have to worry about this with an open BOV, which is why mine is recirculated, even with my EMS.

7 psi is 14", approximately. That means if your idle vacuum is more than 14", your valve is likely opening, which gives the potential for ingesting unfiltered air. Yikes!

All this assumes the pressure drop at max boost and redline RPM doesn't exceed the spring pressure, which it really shouldn't. If it does exceed 7 psi, it's DEFINITELY time for new charge pipes and intercooler!

[myshtern]

The BOV will open at idle. The typical engine idles at 18"-ish at this altitude with stock cams. Your spring therefore has to overcome this plus 1-2" positive pressure coming out of the turbo, even at idle. You only have to worry about this with an open BOV, which is why mine is recirculated, even with my EMS.

7 psi is 14", approximately. That means if your idle vacuum is more than 14", your valve is likely opening, which gives the potential for ingesting unfiltered air. Yikes!

All this assumes the pressure drop at max boost and redline RPM doesn't exceed the spring pressure, which it really shouldn't. If it does exceed 7 psi, it's DEFINITELY time for new charge pipes and intercooler!
Wait, i didnt understand any of that. What do you mean the engine idles at 18"?

I thought that the vacuum created in the intake while off throttle will force the valve to open because the pressure is greater on the other side. What is all this mumbo jumbo about charge pipes and inches?

I'm talking about the BOV btw

[Enthalpy]

The overall goal is to have the BOV open ONLY when you want it to. The BOV has a vacuum line that goes to the manifold. Think of the BOV as a simple piston with 3 forces on that piston. 1.) Manifold Vacuum, 2.) Turbo Pressure, and 3.) The Spring.

If that valve is open to atmosphere, you want it to stay CLOSED when the turbo isn't making tons of pressure. Otherwise, you might draw in unfiltered air.

So, the only time you will draw IN air is when you are not boosting. The maximum vacuum you will have in the manifold is during overrun, but you will have very close to that amount at idle.

The inches is "Inches of Mercury", which is a unit of pressure.

So, at idle, you have 18" of vacuum pulling the valve open because you have 18" of vacuum in the manifold. You have 1-2" of positive pressure PUSHING on the valve in the same direction from the turbo's side. The ONLY thing that's keeping the valve closed at that point is the spring, which (in my example) has to overcome a total of 20" of pressure. 20" of pressure is ~10 psi!!

Does this make sense? If not, I will explain it another way. Please let me know if it makes sense. I want everybody to understand!

[myshtern]

I see exactly waht you mean now. I just didnt understand what you meant by inches, but its all clear now. Thanks

[Mark_H]

Without getting too damn technical, I've seen(heard) Tial BOV's open between 5-7psi on cars before. And FWIW they are super quite and I love 'em.

Just for reference, if you have a 7psi spring in your wastegate thats the lowest amount of boost you can run with that spring. A boost controller for example will not turn it any lower.
HTH
Mark