[200q20v] re: stock bypass valve, TBV

Glen Dustin Powell gpowell at ennovatenetworks.com
Fri Sep 15 14:21:32 EDT 2000

I hear what you say but don't follow the logic. Even if the air-flow meter
is 'maxed-out' it is still measuring 'metered air' by defnintion. I think
the point of concern was that the F/TCU would still think that large volumes
of fuel should be injected because the airflow meter sees big airflow, but,
the throttle-plate is closed and no air is entering the engine at all, only
fuel, because the air-meter still thinks there is flow but the throttle is
closed. (and there is flow, but it is bypassing the engine and escaping via
the blow-off valve before the closed throttle-plate)

I remember and admire your ingenuity in using the furnace valve with
success! My guess as to why it works well is again because the idle-switch
would have indicated to the F/TCU to ignore the A/F meter when the throttle
is closed and not inject massive volumes of fuel when the throttle is

The reason I am looking at installing a blow-off valve in the ur-q is to
reduce the tendency to blow induction hoses due to the big spike that
results when the throttle slams shut at high boost and high turbo RPM,
similar failure mode as your IC tank blowing problem, need a place for all
that air to go...  Secondary reason is for improved response on upshifts and
because it should be easier to plumb Vs a bypass valve.

Another random thought on improving response on upshifts - how about a
'turbo inlet valve', an electronically operated 100% sealing valve ahead of
the turbo inlet? This valve is binary in operation - 100% closed or 100%
open and it would normally be open. Only when the throttle is closed on
upshifts, instantly close this valve before the turbo starts to spin-down so
the turbo spins in a partial vacuum for the duration of the closed
throttle-plate/up-shift. This should result in higher turbo rotational speed
(and potential boost level) when the shift is completed. When the throttle
starts to open back up after the shift the 'turbo inlet valve' re-opens for
the turbo to take in another gulp of fresh air.



-----Original Message-----
From: Sylvester, Mike [mailto:Mike.Sylvester at sycamorenet.com]
Sent: Thursday, September 14, 2000 3:06 PM
To: 'Glen Dustin Powell'; 'Brett Dikeman'; 'Paul Friedenberg';
Brian.Link at Level3.com; fussball_3 at hotmail.com
Cc: 200q20v at audifans.com
Subject: RE: [200q20v] re: stock bypass valve, TBV

If you have a blow-off valve that opens at a set pressure (e.g. 25psi)you
will not be blowing off metered air, because the "air meter" is already
max'ed out anyway.

In my previous 10v turbo I installed a hotwater heater pressure relief valve
into my intercooler that opened at 25psi.  I had to do something after a
side tank blew off the IC.  Everything worked normal unless you quickly let
off the throttle after full boost.  Then when the pressure spiked between
the turbo and throttle body the pressure valve vented anything above 25psi.
I'm sure the air metering is railed at 25psi.


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