MarkRobinson

BTW: the famous red 928 burnout was me back in '99. I need to do another, can't stand to be upset by another good burnout.

ehall

Okay thanks, but where did this come from? Got a link? I'd like to get some additional info. Thanks. E

Zero10

Did you try it with the lines to the BOV capped off?
If it holds boost just fine in that situation, check what the line feeding the nipple on the top is doing. If I read this right, you already tried your BOV in a friend's car, and it works?

toddk911

Ehall:

I sent an email to a company selling a lot of BOV and asked them what is the difference in spring rates and that was his email reply.

MarkRobinson

I'll try the valve backwards & with the nipple capped, see what happens. I'm wondering if my valve is too close to the turbo: as it's about 5" off the compressor housing, but if anything were to theoretically be askew, it would be that It couldn't recirculate enough & possibly hold more boost...I'll have to dick with it a bit I guess

Laust Pedersen

The cork-screw flow pattern just out of the turbocharger has a higher (than mean) pressure at the periphery. Depending on the specific plumbing to the BOV it may simply get much more pressure than the manifold pressure, triggering it to open.

Laust

toddk911

Could this be a VE issue?

MarkRobinson

Keep in mind that I am pressurizing the side of the BOV, which would hold it closed, regardless of increased pressure due to turbo proximity. My vacuum line to the BOV is taken from the throttle body (long vacuum line)

Laust Pedersen

To the best of my knowledge the BOV opens due to a pressure difference between its side port and control port, which is why it will stay closed at a 30 psi boost pressure (at WOT), but will open if you close the throttle (change gear) at for example 15 psi.
I assume your control signal is taken after the throttle plate and that it senses static and not the combined static and dynamic pressure.

Laust

MarkRobinson

correctamundo.

Laust Pedersen

It is as if you didn’t catch my first point (or politely avoided a comment because you don’t agree ), namely that out of the turbo comes a swirling air flow much like a tornado, which will have a cross-sectional non-uniform pressure distribution. The mean pressure, which is the pressure that the BOV’s side port should see, is more than the pressure at the center of the tube and less than the pressure at the inside wall of the tube, which according to your picture is what the BOV’s side port is seeing.
That theory could be substantiated or disproved by doing two simultaneous real-time pressure measurements.

If you do get adequate boost pressure with the long blue line clamped, then the above would be my best guess.

Laust

MarkRobinson

Doh, for the mock-up, I have the BOV in backwards. Geez, it's been a very long week. Yes, with that picture, I'm boosting against the spring, which is opposite of what i"m doing now.

I may move the BOV to the intake (post intercooler) ala 951 this weekend & try it like that, that's how I did it before, though not as "clean" a design.

ehall

thanks

evil 944t

[QUOTE=MarkRobinson]Doh, for the mock-up, I have the BOV in backwards. Geez, it's been a very long week. Yes, with that picture, I'm boosting against the spring, which is opposite of what i"m doing now.QUOTE]

Do I win a prize? Is it backwards? I have seen BOV's (non recirc) built into the intercooler. I don't know what or how your EMS works but thats an option.

Laust Pedersen

I thought the inverted BOV was part of the experiment mentioned in post # 20.

It should be possible to catch the mean pressure just out of the turbo, but that will require some baffling and/or angling of the outlet to the BOV. Some careful measurements and luck are also needed.

True, that set-up certainly looks clean and elegant.