[BiturboS4] RE: boost & engine load

Edwards, Dave Dave_Edwards at iOra.com
Wed Nov 13 09:43:52 EST 2002

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.

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