The Kawasaki Z650 and its Ninja 650 stablemate share many design and mechanical characteristics. While the Z650 possesses a naked style, which Kawasaki describes as "minimal bodywork," the Ninja ...
With the same parallel-twin engine that you find in the Ninja 650, the Z650 offers power with liquid cooling for the warm-weather stamina and temperature stability it brings to the table.
Both are in different category.zx6r is a track oriented bike in the super sport segment(600 cc with adequate power,it stands behind the litter class) Ninja 650 is an excellent sports tourer.