As above FRST with an 1800 ZVH and de-comp plate.

Blue smoke when driven above 2.5k, no smoke when idling and up to say 4k at a stand still? No oil on spark plug either.

Drives ok so not valves etc?

Compression test read as follows

1 - 11bar
2 - 11bar
3 - 10bar
4 - 5bar

Got to be a piston prob or HG??