why is oil coming from my valve cover where it runs to the fresh air duct?

i just built the motor and turboed the engine, done 300mile brake in then had it tuned to 16psi boost. while tuning everything was fine and went well, afterwards i noticed under boost it was spitting oil out of the valve cover line that is supposed to hook to my "fresh air duct" when i noticed this i did a compression teste and all 4cylenders read 150psi which i think is correct since i put weisco 8-8-1 pistons in it, i also installed eagle h-beam rods, chromoly rings, supertech valves and springs with titanium retainers, plus cleivite bearings, along with arp head and main studs and a walboro 255 lph fuel pump with apexi neo ecu. so i dont see why i would b having any problems. plz help me understand why this is occurring with the oil issue, thanks :)