Both ways will work, HOWEVER... - Saab 9000 Bulletin Board - Saabnet.com
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Both ways will work, HOWEVER...
Posted by Kyle [Email] (more from Kyle) on Wed, 2 Jan 2002 10:37:00
In Reply to: By pass valve - once more ....., Tapani, Wed, 2 Jan 2002 06:28:53
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I was asking this same question a few months ago. I'm actually one of the people that pointed out to Quasi that his valve is installed the opposite way from stock, which prompted him to write about it on his site.
I have tried it both ways, and both will work fine. However, there is definitely a difference between the two configurations.
From my perspective, the bypass valve has a spring pressure that is calibrated to hold up to a certain PSI (probably about 15psi) with pressure pushing ON the diaphragm. This acts as an additional boost limitation in conjunction with the wastgate as actuated by the APC/BPC valve (or in my case an MBC).
On the other hand, if the diaphragm is PERPENDICULAR to the pressure, then it will take more pressure to push it open, thereby changing its performance slightly. The pressure "blow-off" between shifts will be sharper, and more abrupt.
Regardless of configuration, the diaphragm will open under vaccuum between shifts. The main distinction is whether the valve will open at all under throttle as an additional pressure relief, and the nature of the pressure relief under vaccum, when it occurs.
I bought a metal bypass valve from Stratmosphere.com because it never fails and I can adjust the spring tension. Yes, it is more expensive but it also works better. I noticed that with the pressure pushing ON the diaphragm (actually a cylinder), the spring tension had to be much higher in order to prevent the pressure from pushing it open at low boost.
My advice is to try it both ways and see which one YOU like better.
ENJOY!
-Kyle
posted by 64.65.19...
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