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Still troubleshooting some issues with my SP58GT BK:

The car is an auto and after each shift (WOT) boost will drop from 17 psi down to 12, accompanied by a hissing sound, and slowly regain back up to 17 psi.

The obvious answer is a boost leak however I have run a boost leak check to over 25 psi and nothing is leaking.

Is it possible that the dynamic pressure of an actual running/boosting engine is uncovering a leak that my static pressure leak tests are not finding?

Any ideas???
 

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i'm having the same problem but with stock twins. If I floor it in 3rd at around 50 mph or 3900 RPM, once it hit 4200 it would boost up to 1.21 and hold it there until around 6 where it would drop down to 1.1 by redline....once I shift into 4th, it would go up to 1.17-1.18 and then drop down to 1.1 at redline.

Some days when I floor it in 3rd at 3700 RPM, it would sustain boost of 1.25 all the way to redline when i end up shifting at redline and when i shift into 4th gear, it would be at 1.20 and continue to drop slowly.

Does anyone know whats causing this. Here is a little info. I'm 6 spd with the spring mod on my wastegate. BPU with intercooler. I'm in perm TTC. Any light to this matter is much appreciated. Thanks.
 

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i'm having the same problem but with stock twins. If I floor it in 3rd at around 50 mph or 3900 RPM, once it hit 4200 it would boost up to 1.21 and hold it there until around 6 where it would drop down to 1.1 by redline....once I shift into 4th, it would go up to 1.17-1.18 and then drop down to 1.1 at redline.
definatley a week wastegate .
try to use a stiffer spring on your springmod or tighten it out , that shall fix it :)
 
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