[jrenfrew]

I have a 78 928 and if your car is an early 79 then you might take this as your first line of trouble shooting....

In 78 and early 79 Porsch has a crank case venting pipe that is fairly short and goes from the oil fill into the air filter air box. The hose runs along the drivers side of the engine. You might try taking a look in the air box (remove the filter) and see if there is a lot of oil sitting in there. If there is you could try plugging the vent pipe and go for a test drive.

Otherwise, I'm sorry to say rings are your next most likely suspect. Plus if the car is pushing a lot of oil from the vent pipe (which was a bad design and changed in later 79) then it's going to be due to a lot of case pressure most likely caused from a ring problem. Valve guide troubles typically show up when the car is dead cold or under heavy de-accelleration it will smoke good. Under accelleration the intake vaume is at it's lowest therefore makeing it unlikely to be oil getting by the values.

Hope that helps shed some light!