Re: '91 200q turbo bypass valve in's and out's

[Angela Dupin <dupina@crisny.org>]

your friend's hook-up is correct.  the small manifold connection adds to 
the internal spring to keek the valve closed when under boost.  in this 
fashion the valve will open sooner when vacuum is present in the manifold 
since it will be helped by the high boost on the inlet side under the 
valve disc.

All the best,

Phil

> 
> I was looking under the hood of a friend's '91 200q and noticed that his
> turbo bypass valve had the input and output ports reversed from mine.  Now I
> am wondering whose installation is correct.
> 
> The bypass valve looks like a little cylinder, with a manifold/vacuum port
> on one end of the cylinder and a hose connection on the other end.  Off the
> side of the cylinder is another hose connection.  On my car, the hose
> connection off the side goes to the high pressure (turbo out) hose, while
> the connection opposite the vacuum port goes to the input side of the turbo.
> On my friend's car, it's just the opposite.  
> 
> Based upon how I see the valve operating, it seems like my connection is
> correct, since under turbo pressure it would tend to keep the valve closed.
> If you reverse the connections, turbo pressure would open the valve unless
> there is enough positive pressure from the manifold/vacuum port to keep it
> closed.  Neither of us wants to lose boost.  My connection also seems to
> match the schematic in my Bentley manuals.  But you never know.
> 
> So what's the net.wisdom out there?  Is my turbo bypass valve installed
> bass-ackwards, or is my buddy's wrong?
> 
> TIA
> 
> John Mallick 
> '91 200q
> '84 4000sq (dead master cylinder...any good offers?)
> 
>