You shouldn't be losing much oil at all through old valve stem seals... and typically this is only really seen when starting the engine cold and any smoke disappears after about five minutes. It's possible if they're missing or so far gone as to pretty much be missing but you would have seen this coming a long time ago. It's easy to avoid dropping the valves into the cylinder when replacing seals with the head still in place. Remove both cams, pull the spark plugs, rotate the crank so the current cylinder is at the bottom, feed in 1/4" rope until you can't fit anymore, rotate crank to bring the knot of rope up against the valves. When done with that cylinder's valves, rotate the crank to free up the rope and pull it out. Another way is to use an air compressor to fill the cylinder with enough air to hold the valves up.
Where the engine block and head properly machined before the metal head gasket was installed? Was the rear timing belt cover machined while attached to the block?
Have you done a leak down test or even a compression test? Checked the turbo for oil? Checked the intake? Have you replaced the valve cover seals (DON'T over torque them! They should only be hand tight!)?
See the FAQ about cold air intakes... You may have actually made things worse and any increase you think you see may only be perceptual.
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.
If you're so inclined I'm always more than happy to accept tips via PayPal. 
Tip Jar ---> 
|