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more info from Avi and Scott, RE: Bypass valve orientation?
You should be able to get the Bosch valve for $30-40 in most places that
sell Bosch, look for it in European car magazine, see post below from Scott
"According to the cut-away diagram in the Audi factory service training
booklet, "The New 20V Turbo engine for the Audi 200 Quattro" the Turbo
Bypass valve is shown connected to the Turbo outlet (boost) using the
side outlet which is perpendicular (90 degrees) to the small vacuum
connection. The diagram shows that the boost pressure "should" help keep
the valve closed. The fitting straight across from the small vacuum
fitting should be connected to the turbo inlet (suction). The spring
inside the Bypass valve is shown to hold the valve closed against the
Do you know if the Bosch 0 280 142 102 valve you are using has the
fittings arranged the same way as the stock 1991 200TQ 20V Turbo valve?
(0 280 142 106 I think)"
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of Brett Dikeman
> Sent: Saturday, July 11, 1998 10:27 AM
> To: Phil Rose
> Cc: firstname.lastname@example.org
> Subject: re: Bypass valve orientation?
> >FWIW, nipple forward is the direction on the '91 200q.
> >But you've stirred my curiosity about this cool "designer" bypass valve
> >(and other variants). If the valve spring tension is different in various
> >models, I suppose this must be to account for the varying levels
> of boost?
> >If so, would "upgrading" the bypass valve be a useful thing to go along
> >with ECU chipping? For example, would a chipped '91 200q benefit
> from using
> >a stock S4 bypass valve--or some other? For that matter, is the
> stock S4's
> >bypass valve significantly different (hose dimensions, etc) from the '91
> According to many sources, the Bosch turbo bypass valve used in the 91 200
> is a generic Bosch bypass valve, and a fairly old design; my father's '87
> 944T uses it.
> However, many racing shops sell it, and on their web pages, next to huge
> bypass valves with big chrome junk+everything, is the little
> innocent Bosch
> valve, with a note, something along the lines of:
> "This Bosch valve delivers the best performance of any valve in
> its size"(1
> inch.) The shops usually sell it for about $70. Tried and true, I'm
> leaving it in there :)
> Brett Dikeman
> Hostes alienigeni me abduxerunt. Qui annus est?
> Te audire non possum. Musa sapientum fixa est in aure.
> Ita, scio hunc 'sig file' veterem fieri.