[BiturboS4] RE: Defi/Mach V boost gauge problems

Edwards, Dave Dave_Edwards at iOra.com
Wed Jun 5 12:35:52 EDT 2002

Thanks for posting that - I too will be fitting this gauge in a couple of
weeks and I wasn't sure where to splice my air hose.

Firstly I could be wrong but I doubt that the -ve is on the same scale as
the +ve. When the car is not on boost, it is effectively normally aspirated
so there is a vacuum. However this -ve pressure is a lot less than that
produced by the turbos.

However, whenever you are not accelerating, or only lightly accelerating,
you should indeed get a vacuum. Moderate to hard acceleration is what makes

Your absolute peak boost looks right for a chipped car. What does this
settle down to, whilst still accelerating hard? I'd expect around 1.0 to 1.1


P.S. The Euro S4 peaks at around 0.8 bar to produce around 261hp(SAE) and
295lbft torque. Since a chipped S4 can produce over 300hp and about 380lbft
torque, that boost is going to have to go well over 1 bar!

Replied to:
Date: Sun, 2 Jun 2002 19:56:27 -0700 (PDT)
From: Philip Pace <pjpace at yahoo.com>
To: Biturbo <biturbos4 at audifans.com>
Subject: [BiturboS4] Defi/Mach V boost gauge problems

I just finished the installation of the boost gauge part of the Defi HUD. So
when I start the car, I'm at -350 (-.35bar). When I floor it, I can get up
to 1.26 bar (I know the peak hold works). If I'm coasting, it settles at
about -.4 bar and sometimes drops to less than -600 bar. WTF is wrong? I
installed the T adapter just near where the brake lines cut through the
firewall (similar to
this: http://www.audiworld.com/tech/pics/tcon.JPG) and the hose is only
about 8" long. Did I do something wrong, or is my car screwed up? I have an
APR chip, so boost should be above .6, but 1.26?!?!?!!! Thanks for any
     -Phil P.
P.S. I do have the HUD set on gasoline turbo, otherwise I got no reading or
a really REALLY odd reading (gasonline NA and diesle turbo, respectively).

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