The reason I asked all the questions about the exhaust is that excessive back pressure will cause the symptoms you just described. One guy on the board found he had a loss of boost because his cat disintegrated and clogged up his muffler.
It would be nice to know what is stock regarding the engine and what is not. We know you have a different turbocharger (k-27 7006) and stock ignition. It always helpful to diagnose a problem if we know more about the patient. 
Also, I'm a firm believer in "cause and effect". The last thing you did to the engine was change the ignition timing......that would be the first I area I would check.
Put your hand over the output of the wastegate and see if you can feel any exhaust pressure.
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Dave
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
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