Atkinson Differential Engine

[Charlie]

Hi, my name is Charlie and I'm building this engine. To increase the compression ratio I will make the pistons slightly bigger in diameter but also add a flat crown to the working piston, the one on the right, leaving just 1mm clearance to the opposing piston. Importantly, I will mill a one third moon shaped recess in the area adjacent to the spark plug down to the original piston length.
Hope this will help anybody. Regards.