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This in response to an ealier post re using pressure regulators and relief valves etc.
Folks were commenting on the drop of pressure at high rmp's, expecially in low gears.
This happens as the pressure tap on the compresor housing is not very good as a pressure tap. If it was a reasonablle analog of whats happening at the manifold, things would be better.
First, the pressure drops becuase of the pressure losses across the IC.
Second, the flow at the compressor housing pressure tap is very complex, not developed and just not very useful.
If you take a presure tap from the manifold with a ball-spring MBC or just above the throttle plate with a bleeder, the boost will only taper if the turbo cannot deliver. But this location imposes time delays that result in excessive overshoot in cool or cold weather.
I cut a hole in the top return tube of my (old style) IC, and bonded a pressure tap there. I do not have any strange pressure drops in the lower gears. There is still some boost taper, but things are much better. The taper is caused in part by pressure losses between that location and the manfold.
I have considered putting a tap near the bypass valve. This might work better. I have also considered a valve to switch between the existing or similar tap and the manfold after a time delay to let the initial transients settle down.
So the bottom line is that the compressor housing sucks as a pressure source. You need to get after the IC core, but also keep the hose lengths short.
If you use a manifold pressure tap for the summer, you will be quite impressed with the boost at high rpm's.
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