[s-cars] Forge BPV's ??(diverter valves)

CaptMagu at aol.com CaptMagu at aol.com
Fri Jan 31 11:03:17 EST 2003

Joern and Mike

This was originally posted to the kremmer list but I thought some of you
would enjoy this too.

Joern, get rid of that Bosch unit before something gets sucked into your
turbo. First things first.

On the charge air line running from the turbo to the I/C we have a 28mm bib
plumbed to a section of 63mm aluminum pipe. The BPV is plumbed between this
charge air pipe and the turbo inlet. Additionally there is a vacuum line bib
at the top of the valve that is pressurized from the intake manifold. As the
biturbo list diverter valve test and article reveals the piston type valves
can be plumbed either of 2 ways. We had them plumbed conventionally with the
charge air pressure line feeding into the bottom of the valve against the
spring. The problem here is that in high flow(make that Happersized turbos)
you get too high a pressure differential. The boost pressure within the
charge air line pushes against the piston/spring and intake manifold pressure
from the top to prematurely open the BPV. This pressure differential exists
because we are approaching if not exceeding the throttle body and intake
manifold's ability to handle flow.

This wasn't that much of a problem for me before that Mike Pederson talked me
into cleaning up my intake tract with the Pederhousen Big MAF and the fluting
to my I/C. Since the cleanup, I now flow significantly more air and thence
the problem with the throttle body/intake manifold. We've got all this air,
we just can't get it all to the very clean head.

I have recently talked to the techs at TurboXS and they did indeed state that
for big hp applications they now recommend plumbing the valve backwards or
sideways. The charge air line is now plumbed into the side of the valve. The
TurboXS valve does have a split piston with a shaft inbetween. With the
charge air coming in the side it pushes against one side and the other. This
nullifies the effect of the pressurized charge air. When you shift and go to
vacuum, the top of the piston is pulled up, activating the valve and divert
ing the air to the turbo inlet.

Finally, one last thing. On the stock urS-cars the turbo to crossover pipe
hose has the plumbing for the BPV. It comes off the curious snake hose affair
on its way to the MAF to turbo inlet hose. Why did Audi plumb this loop in
there? A lot of other applications also have a similar extra hose plumbing.
Curious. That's all I know about BPVs, honest.

Hap, no longer prematurly bypassing in Evergreen, Maguire

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