swerv's right.

Machined is not the same as skimmed. If you skim 'em you bugger up the squish area.

To answer gurnE's original question. Assuming the engine is untouched from new then fitting 4x4 pistons will bring the CR down to 7.8:1.

I'll be going greys on a Stu live map with standard 8:1 fairly soon. That's the plan anyway.