[s-cars] While we are on the subject of WGFVs...

[Tom Mullane]

Hmmmm.

Dave,

First off, no offense taken.  Like you, I consider these discussions a
great forum for learning.

I can't find any holes in your argument below.  I can even buy the
venturi effect; in theory it's possible.  The boost numbers seem to
contradict reality....my reality anyway.  But unfortunately (or
rather: fortunately) I am many mods and many years from stock, so
perhaps that has skewed my reality.   At one time, while trying to
diagnose my evil overboost issue, I had a vacuum/boost gauge plumbed
into the line between the WGFV and the WG and taped to the windshield
of the car.  I wish I had paid more attention to vacuum side; I was
just looking for boost.

Makes me almost wish my car was still stock so I could do some
testing....naaaaah.  :-)

Tom

On 1/11/06, Djdawson2 at aol.com <Djdawson2 at aol.com> wrote:
> In a message dated 1/11/2006 7:10:43 PM Mountain Standard Time,
> tmullane at gmail.com writes:
> I can't explain the mysteries of the universe, but I do know that the
> basic WGFV functions as Teddy and I described it.  When power is
> applied, all ports are joined.  All you need is a WGFV, a battery, and
> breath of air to test and confirm this.
>
> Tom,
> I am well aware that what you and Teddy have stated is true.  I have never
> debated that fact.
>
>
> Remember that the spring only needs to hold the WG shut against
> exhaust gas pressure inside the exhaust manifold.
>
>
> I am also well aware of this fact.  I would guess that I've been to as many
> turbo system design seminars as anyone on this list... as fleet management,
> design, and specification (mostly diesel and natural gas turbo vehicles) is
> 75% of what I do for a living.  I'm not trying to be conceited, but I do
> know what I'm talking about when it comes to turbocharging systems.
>
>
>
> The only boost to affect the spring comes from the WGFV when it is closed.
>
>
> Agreed.
>
>
> Exhaust manifold pressure is related to the exhaust system flow, not boost.
>
>
> Agreed... partially.  As boost builds, so does exhaust manifold pressure...
> and the only relevant pressure to our discussion is that found between the
> cylinder head, and the turbine wheel.
>
>
>
> Think about what happens when you disconnect the WGFV from the WG -
> boost goes sky high.
>
>
> No... it will only build to about 14-15psi.  That is why it is called a "1
> bar" spring.  The spring is designed to provide just enough "push" to hold
> the WG shut to 14.7psi... no more, no less.  AND, it only performs to this
> spec if it is used in the original configuration... meaning EM and turbo.
> Throw a header and a different turbo into the mix, and the pressures
> change... and so will the boost level allowed by the spring.
>
>
>   In this case, the only thing that can overcame the spring and open the WG
> is pressure of the exhaust inside the manifold.
>
>
>
> Yep.  But knowing that the spring is only good for 14.7psi of boost
> (unassisted), how would you explain being able to run double that?  The only
> explanation is vacuum to the bottom of the diaphragm of the WG.  I did a
> little search on the web, and the best drawing I could find without turning
> this into a big project, was this:
>
> http://www.2linc.com/venturi_vacuum.htm
>
> As you can see in the diagram, if all 3 ports are open (which they are in
> the WGFV when power is applied) you have created a venturi vacuum generator,
> with pressure entering the side of the fixture, just like our WGFV.  This
> creates the vacuum that holds our WGs shut.
>
> You can prove all of this to yourself with one simple test.  Clamp or
> disconnect the line to your WG and see what boost you can achieve.  It will
> only be about 15psi.
>
> If you want to take it a step further, connect a vacuum gauge to the line
> between the WGFV and the WG.  You WILL see vacuum there, and it is what
> helps the spring keep the WG shut at boost levels above 15psi.
>
> I hope this email doesn't sound blunt... it wasn't intended to... I do enjoy
> the discussions, and consider them friendly.  I hope you do too.
> HTH,
> Dave