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Originally Posted by twiceblown
Also, FWombat, do you have data for the 3K and below range? I'm curious to see how much variation occurs in the lower RPMs that leads to such a decrease in boost threshold or increase spool with the 3" exhaust (we've all felt the changes). Currently, at 4K, stock pressure drop across the turbine is 11.5psi and the 3" is 11.25psi. So, from those #s, i wouldn't think that any turbo that would spool at 4K or below would see any difference in boost threshold (though the practicality of this obviously is different). Am i missing something?
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I went back through my logs, but most of my pulls started in the 3-3.5 K range, so I probably didn't have consistent data below 4k RPMs. However, on the pulls that I didn't have lower-RPM data for, the difference between stock exhaust and the 3" exhaust was negligable until 3.5-4K RPMs.
I think the lower-RPM spool difference between exhausts is more about the exhaust having a smoother, less turbulent path that preserves velocity better.
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Originally Posted by twiceblown
I think he said 15psi holding 13 to redline. With those increases in differntial pressures pre and post turbine, i'm guessing that his wastegate is being forced open causing the drop in boost pressure. a log of how the boost solenoid is doing could show that, couldn't it?
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The tests were all at about 15 PSI peak dropping to around 13 PSI at redline. I held the boost solenoid at a constant duty cycle in order to get more consistent pressure measurements -- error correction in the boost control makes for a wavy pre-turbine pressure shape as the flapper opens and closes.
As the car gets into higher RPMS and the pre-turbine pressure rises, the WG flapper is absolutely being forced open, as evidenced by the falling boost pressure. I'll go into more detail in another post...
- Brian