How big is the engine in a Mazda 323 car?

It is going to depend on what model you are buying obviously. They come in a variety of sizes ranging from 800cc in 1963 to the 2.0 litre models in 2003 just before production ended. In 1963 though, the Mazda 323 was not known as a 323. It only had it's name changed in 1977 although it was still known as the familia in some parts of the world. All engines were a small 4 cylinders.