you said your getting white smoke blowing at high RPMs?
This may not be relevant at all, but my step father had an old truck, he wasted the motor on it, i rebuilt it, and it ran great no smoke or nothing, until he got it going in (im guessing 3rd gear.. old chevy auto) and up to about 65 mph.. it would start blowing white smoke. But any gear lower than that speed it would be fine.
He had a micro fracture in the cylinder wall, and it only caused a problem at high speed, and higher revs in the engine, the higher rpms, would raise the cylinder temp and overall engine temp (not to mention the turbo) significantly which could cause something to open up, that doesnt during a compression test.
Maybe there is something like that going on, that only shows itself up in those circumstances. heat makes all the difference.
Spark Plug tip reference
Incorrect Heat Range
APPEARANCE: The effects of high temperature on a spark plug are indicated by clean white, often blistered insulator. This can also be accompanied by excessive wear of the electrode, and the absence of deposits.
CAUSE: Check for the correct spark plug heat range. A plug which is too hot for the engine can result in overheating. A car operated mostly at high speeds can require a colder plug. Also check ignition timing, cooling system level, fuel mixture and leaking intake manifold.
