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Re: Dump valves (was Max boost)

Dan Hussey said in regards to a bypass valve:

>  THE THING I DON'T UNDERSTAND IS why it would create any more of a rich
>  condition (off full throttle) than without one!???  I really can't figure
>  why it would!  I mean, that pressure (air) is not entering the intake
>  since the throttle plate is closed.  So, why does it matter what happens to
>  this back-pressure.  It can just run upstream and cause your turbo to stall
>  create more problems.  And, even if it runs a little rich just off throttle
>  (littleraly for only a second) would it creat any problems?  I have thought
>  lot about about it, and can't see why installing a bypass valve would
>  any problems, but I don't actually have one.  Anyone out there with a
>  view or any different thoughts....I'd like to hear them.

The bypass valve won't really cause a rich spike, although a blow-off valve
will.  With a bypass valve, all metered air stays in the intake tract, not so
with the blow-off valve.  With the blow-off valve, metered air is released
directly into the atmosphere from the intake system through the blow-off
valve.  The fuel injection system "thinks" more air has gone into the engine
than really has, and meters an amount of fuel to match producing the overly
rich air/fuel ratio.  This can cause premature wear on the cat. and O2 sensor
(maybe cool flames out of the downpipe too).  How bad it actually is surely
the subject of debate, but IMHO, the bypass system is the way to go.

Personally, I have never seen an Audi (street car anyway) with a blow-off
valve, but plenty of 5ktqs, etc. with fabricated bypass systems that do work.

Steve Eiche