PSI positive. This would be the expected boost with a chip. Or was it 2 bar positive +24 psi???? If it was indeed the later I would be looking at the n75 valve and related plumbing to the waste gates. A smoke test wouldn't show a leak from the n75 to the wast gate since the solenoid could have been in the closed position.

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04 Allroad 6 speed, GIAC chip, AWE intercoolers, Allroad/RS6 fender liners, RS4 covers, Genuine RS6 5 spokes in titanium with correct offset no spacer (lots of etka searching for that), Front & rear RS6 Brakes, H Sports, RNS-E, DVD, Bluetooth, BMW snap in adaptor for the Razor in the console, All tig welded 321 stainless custom exhaust (made by me), Custom S6 instrument Cluster & a Digital boost gauge fit perfectly in the mirror where the compass was.

04 Allroad 2.7 6sp.
01 S8 stock other than Bi-xenon's with Euro lenses
1992 Porsche 968 (mint Green)
1989 Porsche 944TS
1997 T100
1975 280z sky blue