While I was still able, I determined the compression ratio of the A112 engine after all the work I did. With a little creativity it was possible to measure the size of the combustion chamber, the rest was just using old math knowledge.

To determine the size of the combustion chamber I greased a CD with petroleum jelly so that it stuck to the head and no water could leak out. Then I filled the combustion chamber with a large and a small syringe until the water just entered the opening of the CD. After multiple filling / cleaning / filling sessions the size was found to be 20.5 cc. The other details are:

 850 compression ratio850 cr

I am satisfied with a 9.7 compression ratio. My intention is to build an engine for a Fiat 850 that can easily keep up with all sorts off traffic, not a racing monster.