Ok, my friend has a 86 Z31 turbo. He recently had the motor replaced after the old motor developed a rod knock. He looked into rebuilding the stock motor, but decided to just have it replaced with a low mileage JDM VG30ET as it ended up being about two grand cheaper than any rebuild he was quoted. After the swap, the exhaust smoked at startup, but quickly went away as the car was driven and warmed up. The shop ensured him it was just from the motor sitting in the shipping container and would go away with some miles. He's driven the car in excess of 150 miles since and has had the oil changed. The car has a new cat and a new exhaust. When I watched the car warm up, I noticed alot of condensation coming out of the tailpipe with the A/C off. I'm thinking the motor has a bad head gasket and it's leaking coolant into one of the cylinders, but I would like a confirmation before we go tearing the heads off the thing. Here's the video, lemme know what you guys think.
YouTube - 300zx smoking problems
**edit**
BTW, the engine runs strong, doesn't stumble or idle bad.