[urq] Re: Throttle Body Port

[Ingo Rautenberg]

Ben,

You know that answer...

Just think of the physics.  Anything after the turbo can have high or low
pressure (boost / vacuum).  Which is why you have the check valves for the
diff locks.  The only area(s) where this is not the case is from the igloo
(assuming you haven't converted to 034EFI or similar) to the turbo intake.
So anywhere there should give you the vacuum readings you're looking for (I
would think).

Ingo

----- Original Message ----- 
From: "Ben Swann" <benswann at comcast.net>
To: "Ben Swann" <benswann at comcast.net>; <urq at audifans.com>;
<quattro at audifans.com>
Sent: Thursday, April 14, 2005 10:42 AM
Subject: [urq] Re: Throttle Body Port


> I tee'd a line off this and ran to a guage inside the car.  Results were
not
> quite as anticipated.
>
> The port is under vacuum in most cases.  The most vacuum occurs as the
> throttle body is opening up - as in under acceleration while pushing the
> pedal down.  Vacuum only goes to around 0.8 bar  (-5 PSI) and positive
> pressure to only around .3 bar/4 PSI - these are rough numbers, but show
> what is happening.  The positive pressure occurs only under maximum boost
> when the throttle is held steady or perhaps closing.  I beleive it is
> venturi effect mostly, but sometimes manifold pressure comes into play.
>
> This port is noramlly used to control the Carbon Canister Valve, and I was
> going to try to use it for another purpose.
>
> Where might one get a vacuum source that is directly proportional to the
> airflow in the engine and not related to boost?  That is highest vacuum at
> max flow which is perhaps even at high boost.
>
> Ben
> ----- Original Message -----
> From: "Ben Swann" <benswann at comcast.net>
> To: <urq at audifans.com>; <quattro at audifans.com>
> Cc: "Ben Swann" <benswann at comcast.net>
> Sent: Friday, April 08, 2005 10:55 PM
> Subject: Throttle Body Port
>
>
> > I'm still trying to confirm what this port does exactly.  Not what it is
> > being used for, but weather it is alsways vacuum  and directly
> proportional
> > to the airflow through the throttle body and weather the engine is under
> > boost or vacuum doesn't matter.
> >
> >
> > [What exactly does the throttle body port on the UrQ(and others) do?  By
> > that, how does it behave?  Is it using venturi effect to induce
increasing
> > vacuum as flow through TB increases.  Is it always vacuum - even under
> > boost.  Is its highest reading at max flow?
> >
> > Anyone know for sure?
> >
> > Ben]
> >
>
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