A high-revving 400 for the 21st century?
On February 1, 2023, Kawasaki officially launched the all-new Ninja ZX-4RR KRT Edition in the U.S. Is it an answer to the enthusiasts here who like to moan about all the cool, smaller-displacement bikes we don’t get? Let’s dive into the specs and see.
It’s powered by a shiny new, high-revving, four-stroke, liquid-cooled, dual overhead cam, four valve, 399cc, inline four-cylinder engine. Bore and stroke are 57.0 by 39.1 millimeters. Kawasaki’s peak torque figure for this little powerplant is 26.5 pound-feet at 11,000 rpm. Redline, by the way, is over 15,000 rpm. The compression ratio is 12.6 to one. This mill is mated to a six-speed gearbox with an assist and slipper clutch fitted as standard equipment.
Kawasaki says that it used die-cast aluminum cylinders and cast aluminum pistons in the creation of this engine, with a molybdenum coating on the piston skirts to increase durability. The wide bore of the cylinder allowed Team Green to use 22.1mm intake valves and 19.0mm exhaust valves to enhance airflow, and the narrow 24.8-degree valve angle was designed with combustion efficiency and engine compactness in mind.
Other trick bits inside the engine include lightweight forged camshafts and triple-rate valve springs, two-stage machining on the intake ports that’s similar to what’s found in the Ninja ZX-10R, a lightened flywheel, and 34mm electronic throttle valves to aid with Team Green’s electronics package on this bike—because yes, of course it has an electronics package.
