RE: Re: Bypass valves and turbos

[QSHIPQ@aol.com]

In a message dated 9/19/99 4:42:26 PM Central Daylight Time, OorQue writes:

> When I originally installed the bypass valve on my 200q, I used the normal 
> connection method and found it started to bleed off boost around 8-9 psi.  
I 
> then reconfigured things using the double-check valve setup and it stayed 
> closed all the way up to the 12-13 psi of boost I was then running ... 
highly 
> recommended, if you must use the Bosch valve and not something that's 
better 
> suited to cars running higher than stock levels of boost.
>  

Jeff, I argue that what you posted above is impossible.  Assuming that the hi 
pressure air is 90 degrees to the nipple (and nipple hooked to back of 
manifold), adding total manifold boost pressure + 9psi of baseline spring, 
it's impossible to have valve cracking unless you have a bad valve.  Think 
about it, a diaphram with 9psi of spring pressure plus 13psi of boost 
pressure, shouldn't crack until 22 pounds of boost, (which in turn, is 
impossible with a 13psi mod).  In fact, if you put total manifold pressure on 
top of 9psi of baseline spring pressure, the valve will never crack until the 
diaphram fails.  Unlike the "wastegate cracking" found in Corky Bell's book, 
there is no delay or WGFV, the application of boost on the diaphram is linear 
and equal to the measure of boost in the manifold, in fact the diaphram is 
ALWAYS + 9psi above all boost manifold pressures.  If you hooked up the 
double ck valve (DCV) and it worked to 12 to 13psi, then you reinstalled the 
valve back in correctly and/or you never had boost pressure to the nipple in 
your earlier install.

One could argue that the boost bleed (DCV) method with a 2bar mod lengthens 
the bypass valve life (since it's only hit with half the boost than normal), 
but it doesn't change the cracking pressure or the valves performance.  When 
I see the above (most times from a dealer install), I first ck to see that 
the nipple is 90 degrees to hi pressure.  When it's inline with the pressure, 
you get cracking and it's nary impossible (read: it takes forever, try it), 
once the valve cracks, to get it back shut again.

HTH

Scott Justusson