[BiturboS4] RE: boost & engine load

Michael Kuriger michael at isuzu-mods.com
Wed Nov 13 12:02:19 EST 2002

[ Picked text/plain from multipart/alternative ]
that exhaust you can feel with your hand at the tail pipe is not nearly
enough to spin up a turbo and create boost.  if you were to remove the
turbo from your exhaust manifold, and hold your hand here while under
full throttle and undel a load you would lose your hand.

the diverter valves open when there is a vacuum (which only happens at
cruise or decel) if a diverter valve fails to open it will not have much
if any affect on boost under load.  It's purpose is to release the
pressure inside the intake when you let off the gas.  otherwise this
pressure has nowhere to go except back through the turbo backwards.


David wrote:

>I still don't see any mecanical reason for the boost to stop when in
>neutral, or when there is no load. Try to put your hand at the output of the
>exhaust when you are accelerating in neutral (I know, you should have a
>really long arm, or a friend to help you). You will feel a big increase of
>the gas flow. This flow is supposed to generate, through the turbo, the
>boost. I guess the reason is electronic : both wastegate valves and diverter
>valves are controled by the Motronic system.
>Quoting the "internal-use-only 2.7t self-study program", :
>"The charge pressure of both exhaust gas turbochargers is controlled via the
>common charge pressure control valve N75 (...).
>The Motronic ME 7.1 activates the solenoid valve for charge pressure control
>N75 and regulates the charge pressure via the wastegate".
>Actually I do remember that when I had boost problems a few months ago, my
>ABT tuner in Paris told me to have the N75 checked (and many other things,
>of course).
>And about the diverter valves, the manual says :
>"Divert air control in overrun :
>The Motronic ME 7.1 activates the electric divert air valve for the
>turbocharger and open the pneumatic divert air valves using this vacuum".
>Doesn't it sound more realistic ?
>1999 S4 Avant ABT
>Barcelona - Spain.
>-----Mensaje original-----
>De: biturbos4-admin at audifans.com [mailto:biturbos4-admin at audifans.com]En
>nombre de Edwards, Dave
>Enviado el: Wednesday, November 13, 2002 10:44 AM
>Para: 'biturbos4 at audifans.com'
>Asunto: [BiturboS4] RE: boost & engine load
>Further to what Phil has written, if you rev the engine whilst in neutral
>there is no boost.
>Also, I have the Defi HUD gauge which as well as a digital readout has an
>analogue display which is effectively a set of lights in an oval line around
>the outside of the gauge. This is quite effective in showing the magnitude
>of boost change.
>When I am accelerating hard, getting over 1bar boost, this line is near its
>end. Then when I change up a gear and shove the gas pedal again, I see the
>line rapidly disappear to vacuum and then grow all the way back to above
>I admit that this surprised me the first time I saw it. I had thought that
>when the throttle is closed when changing gear, all that happened was that
>the DVs opened. This can't be the case. If it were then as soon as I opened
>the throttle again, the pressure would build up much more quickly than it
>I assume that when the engine is not loaded, the wastegates are opened?
>Anyway its changed my driving style when I want to go fast: Firstly I try to
>stay in a lower gear (I have a bad habit of lazily driving around in 5th and
>6th), and secondly I try to avoid changing gear.
>Message: 11
>Date: Tue, 12 Nov 2002 08:16:25 -0800 (PST)
>From: Philip Pace <pjpace at yahoo.com>
>Subject: RE: [BiturboS4] no siren
>To: David <goodson at menta.net>,
>	Michael Kuriger <michael at isuzu-mods.com>,
>	Bill Neilsen <wneils at hotmail.com>
>Cc: biturbos4 at audifans.com
>I'll confirm it. I have a digital boost gauge and when you hit the throttle
>out of gear, it will go all the way to 0bar (no boost, no vacuum). I've done
>this a lot, as it's fun to see the car get perfectly to 0 and then drop back
>down (ok
>- I sit in traffic a lot).
>P.S. Were you going to do some S4 website in Spain/Spanish? If so, how's
>that plan going? If not, you know who that was?
>--- David <goodson at menta.net> wrote:
>>Really ? I don't understand that. Could someone with a boost gauge
>>confirm that "there is no boost without load" ?. I thought there was,
>>because in the workshop when they check boost pressure, they don't use
>>any rolling-road. David. 1999 S4 Avant ABT - Barcelona, Spain.
>BiturboS4 mailing list
>BiturboS4 at audifans.com
>BiturboS4 mailing list
>BiturboS4 at audifans.com


More information about the Biturbos4 mailing list