The engines used by the Ninja 650 and the Ninja ZX-6R are very similar in size. This is part of the reason why so many riders are confused about the difference between them. The Ninja 650 has a 649 cc, DOHC, parallel-twin 4-stroke, 8-valve engine. It has an 83.0mm bore, a 60.0mm stroke, and a 10.8:1 compression ratio. It also has a liquid cooling system and a 6-speed transmission. All of this adds up to a bike that Cycle World reports achieves “68 peak horsepower at 8,000 rpm and 47.2 lb-ft of torque at 6,750 rpm.”
As for the ZX-6R, this bike has a 636 cc engine, but don’t let its marginally smaller size fool you. It’s a DOHC, in-line 4-stroke, 16-valve motor with a 67.0mm bore, a 45.1mm stroke, and a 12.9:1 compression ratio. Like the 650’s engine, it’s liquid-cooled and has a 6-speed transmission. That’s about where the similarities end, though. This engine is significantly more powerful. Cycle World reports that it can reach 108.4 horsepower at 13,200 rpm and 45.8 lb-ft of torque at 10,900 rpm. This means that even though these two bikes are of a similar size and weight, and they are both fast Kawasaki motorcycles designed for seasoned riders, the ZX-6R’s engine provides a big boost in both maximum speed and acceleration.
