To determine the CR, you have to know two things.
The volume of the combustion chamber with the piston at TDC, and the swept
volume of the piston.
For example, lets say you have a stock 1600 with a 85.5mm
bore and a 69mm stroke. The swept volume of one cylinder is 396.16cc.
pi(3.14159) * half the bore * half the bore * stroke.
Now to determine the volume of the combustion chamber.
The hard way is to find the deck height with the piston
at TDC. Then you have to calculate the volume of the deck height. To find
the volume of the head itself use a
plate over the bore of the head. Pour in a measured amount
of oil and determine the cc's. Add that to the volume of the deck height.
The easy way is to assemble the engine, set it up on a stand and put a measured amount of oil in the spark plug hole with the piston at TDC on the compression stroke. Be sure both intake and exhaust valves are closed or the oil will run out.
(NOTE: On many type IV engines, this is much easier than method 1 because the pistons have recessed tops which must be taken into account when determining the cc's.)
Let's say that the amount of oil used to fill the chamber is 66cc's.
The volume of the cylinder plus the volume of the chamber, divided by the volume of the chamber is the CR. In this case:
396.16+66=462.16
And
462.16/66=7.00
I have developed a program in visual basic to do all the
math. Click here to download.