Vacuum divider ciruit and MAC11 mods

[Kurt W. Deschler]

Good point about the transducer acting like a capacitor. The volume of the
vacuum line on the transducer side must come into play as well. I'll try
to get a syringe and do some measurements to determine the volume of the
transducer under min and max pressure (unless someone has a spec sheet).
The line volume can be calculated. In any case, the divider should be as
close as possible to the transducer to minimize line volume.

	-Kurt

On Mon, 12 Jan 2004, Richard Tanimura wrote:

> Kurt,
>
> I like the way you think. Lets keep to the electrical analogies. True, you
> want R1 + R2 pretty big to keep the leak to ground (outside air)low. The
> transducer can probably be seen as a capacitor since it doesn't leak much to
> ground. What you might see is a time constant 1/R1*C that is pretty big.
> This will give a lag in your pressure signal. The larger R1 (and C) is, the
> larger the lag.
>
> The CPU is using the pressure signal to determine WGFV pulsing, fuel, etc.
> If you have a big lag in your feedback loop, you might have some automatic
> control problems.
>
> Just some idle speculation on my part.
>
> Rich
>
> -----Original Message-----
> From: quattro-bounces at audifans.com
> [mailto:quattro-bounces at audifans.com]On Behalf Of Kurt W. Deschler
> Sent: den 12 januari 2004 19:03
> To: quattro at audifans.com
> Subject: Vacuum divider ciruit and MAC11 mods
>
>
>
> I would appreciate any feedback about using a series of air flow
> restrictors to extend the range of a the MAC11 pressure transducer. I
> think the following circuit would work:
>
> Vacuum Source >---Flow Restrictor1---T----Flow Restrictor2---< Outsize air
>                                      |
>                                      ^
>                              Pressure Transducer
>
> My intuition is that this circuit should behave like a resistor network
> Pout = Pin*FR1/(FR1+FR2). Fluids experts?? Clearly this would make a
> vacuum leak, but if the restrictors were small enough, it should be
> negligible. I was thinking a FR1/FR2 ratio of 4:1 to extend the transducer
> range to 2.5 bar. The higher ratio keeps the leak side is smaller, which
> is good. Ay ideas on how much flow is needed for adequate response? Could
> even put a check valve on the atmospheric side so that the leak is not
> present under vacuum to work around high idle (split linear curve?).
>
> Longer term, I have a cheapo 2+bar setup in mind using a vacuum divider
> and the cold start valve as a 5th injector. I would line to alter the
> MAC11 program to open the cold start valve, and lean out the injectors at
> the same threshold so that the rest of the boost map can be calibrated
> with the cold start valve open. Any feedback on altering the MAC11 boost
> sampling loop would be appreciated as well.
>
> 	-Kurt
> 	'87 5kcstq
>
>
>
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