Throttle Body Port

[Ben Swann]

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]
>