Hi yes that's it, sounds like its dumping the boost kkk14 turbo/
so, it boosts up, and then WOOSH, your boost is gone?
i would figure out for sure if your buddies car has a over boost protection valve (blow off valve) and if it does, i would just stuff a wine cork in the outlet of it, or else spend a few bucks on the machined aluminum block off plate..
when i was still running a stock VW intake manifold on my diesel, i drilled a hole thru my over boost valve, stuck a rubber grommet on the bolt, and ran it thru the valve, using the grommet to seal the pressure side of the valve off from ever opening again..
or, more than likely, it doesnt even have a over boost protection valve, and its just got a sticky wastegate..
witch of these intake manifolds does his car have? the style on the left, or the style on the right? see that round piece off to the left hand side of the manifold, above the intake runner for cylinder #1? thats the overboost valve, and it was only on the earlier turbo diesels.. later engines had that piece removed from the factory, because it was an un-necessary piece to keep the engine functioning properly..
i imagine it probably has a stuck wastegate.
does it have a boost controller? because to be making over ~.5 bar (7-8psi) and the stock wastegate will be open.. if its making ~.9 bar (13-14psi) then it DEFINITELY has a sticky wastegate..
if it DOES NOT have a manual boost controller, and its boosting to .9 bar, then its time to pull the wastegate off, and clean it, possibly even replace it if its in too bad of shape..