Is there a difference in size of 1.8liter engine piston to a 2.0 liter engine?
Displacement is bore X stroke X number of cylinders. The piston diameter can be bigger or smaller in the 2.0L engine, depending on the stroke. A 2L engine with a very short stroke will have large diameter pistons. Another 2L engine with a very long stroke would have small diameter pistons. So there is no direct comparison in piston diameter from a 1.8L to 2.0L unless you know the stroke of both engines.
Not always but usually. Two things determine the swept volume or capacity of a internal combustion engine. One is the piston diameter and the other is the total distance it moves to get from its lowest to its highest point. The volume of the cylinder multiplied by the number of cylinders gives the capacity.
