[200q20v] re: stock bypass valve, TBV

Thu Sep 14 17:50:26 EDT 2000

I see what you are saying about blown off air being metered.  At the spike
the airflow meter is not railed because although the pressure is high there
is no airflow because the throttle body is closed, but then the blow off
valve releases the pressure, thus allowing air to get metered.

I agree with you about the idle switch.  I don't think the fuel volume will
go up if the idle switch is closed.
In the case of your urq I believe that there is a deceleration valve that
will be open at this time.
Doesn't this valve bypass the airflow meter?

Mike

-----Original Message-----
From: Glen Dustin Powell [mailto:gpowell at ennovatenetworks.com]
Sent: Thursday, September 14, 2000 4:34 PM
To: 'Sylvester, Mike'; '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

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
closed.

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.

???

-glen

-----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.

Mike

-----Original Message-----
From: Glen Dustin Powell [mailto:gpowell at ennovatenetworks.com]
Sent: Thursday, September 14, 2000 9:20 AM
To: '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

I wondered about the blow-off valve issue and too-rich mixtures as a
result... I plan to install one on my 85 ur-q, as it does not have a
bypass-valve stock and likes to blow induction hoses above 15 PSI boost. I
think the idle-switch will tell the F/TCU the throttle is closed and it
might not inject fuel as long as the throttle is closed. This should 'fix'
any rich problems resulting from the blow-off valve letting metered air flow
by the blow-off valve.

Thoughts?

-glen

-----Original Message-----
From: 200q20v-admin at audifans.com [mailto:200q20v-admin at audifans.com]On
Behalf Of Brett Dikeman
Sent: Wednesday, September 13, 2000 9:50 PM
To: Paul Friedenberg; Brian.Link at Level3.com; fussball_3 at hotmail.com
Cc: 200q20v at audifans.com
Subject: [200q20v] re: stock bypass valve, TBV

At 1:21 AM +0000 9/14/00, Paul Friedenberg wrote:
>Mine seems to go out about every 6-12 months, but I tried a valve
>from TAP, and subsequently bent some vanes on my brand new RS2
>turbo, so I would advise sticking with the stock one. Just replace
>it when you hear the WG "chatter." Blau seems to have a decent price
>of $45. Better than a rebuilt RS2!!

Porsche makes a metal replacement valve that costs about the same.
Call any posche parts place and ask for a TBV for a 996 twin turbo.

It's substantially more durable.

>just a passing thought, but has anyone considered putting a blow off
>valve on in place of the turbo bypass valve (ot throttle overrun
>cutout, what ever you want to call it..)  I really have no clue
>about whether it would work, but it would be interesting to find out

Don't.  Blowoff valves dump metered air.  The result is a sudden,
extreme rich condition which eats catalytic converters.  There is no
reason to use a blowoff valve in a street car.  No reason to use one
in a race/track car unless you've done a lot of other stuff to the
car.  The clowns running around with blowoff valves on their A4's are
going to be real sorry in a few years when they have trashed
catalytic converters...of course, I bet all the A4 performance tuners
will be more than happy to sell them "performance" cat converters to
replace those "restrictive" cats on their cars.

Brett
--
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Brett Dikeman				Systems Engineer
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