Porsche 993 Turbo smoking upon start-up?

The most common reason a 993 Turbo smokes on startup is the turbochargers siphoning oil from the engine after shutoff.  This over-fills the drain reservoirs beneath the turbochargers, until oil pushes past the turbochargers' seals.  TurboKraft's 993 Turbocharger Oil Line Update resolves this.   

Less common is the problem from oil draining into the turbochargers from the crankcase.  If your 993 Turbo is experiencing this problem, this is the solution.

History and Technical Notes:
On nearly all air-cooled 911s, oil slowly drains from the dry sump tank into the crankcase when the car sits for extended periods of time.  As the crankcase slowly fills up, oil pushes past the gears of the scavenge pump, back out through the scavenge lines lines, and fills the drain reservoirs beneath the turbochargers.  As the oil level equalizes with the level in the crankcase, it fills the turbochargers and seeps past the turbos' internal seals, into the turbine housings (exhaust) and compressors.  This oil is burned when the engine is started, resulting in clouds of smoke out the tailpipe(s).

The 911 Turbos from 2001- onwards have a nearly identical turbo layout to the 993, and these newer engines had revised scavenge return lines with a high hump in the middle -- an inverted "P-trap" -- to prevent oil from back-flowing towards the turbochargers.  

TurboKraft's 993 Turbocharger Oil Scavenge Line Update:
This package is a simple bolt-in, high-reliability replacement system for the original turbocharger scavenge lines. 
Installation involves simply replacing the original equipment oil lines leading from the turbochargers' drain reservoirs to the scavenge pump. 
This update is highly recommended for all 993 Turbos -- especially those languishing in collections, driven infrequently! 

If your 993 Turbo has a lot of oil in both the exhaust, and turbo compressors and intercooler, we strongly suggest installing both this update as well as our oil feed lines.  The labor required to carefully remove, clean, and reinstall all these components far exceeds the additional parts cost for the 2nd line kit. 
If you or your technician misdiagnosed the problem and the engine starts smoking and dripping oil a 2nd time, you'll regret not installing both the first time.