There's a lot to be excited about with this bike. I can't wait to see this new engine in action.
A class from the past is reborn in Kawasaki’s 400cc inline-four powered Ninja ZX-4RR KRT Edition supersport. And it’s coming to the US this spring.
At the heart of the ZX-4RR is a liquid-cooled, DOHC, 16-valve inline-four displacing 399cc. Bore and stroke measure 57.0 x 39.2mm, which is almost identical to the 1990 ZXR-400R, which measured 57.0 x 39.0mm and displaced 398cc. From there, however, this new engine is fully modern, benefiting from more than 30 years of technological advancement, including electronics that simply didn’t exist back then. Engine redline is 16,000 rpm. Although the US press kit only quotes torque figures (26.5 lb.-ft. @ 11,000 rpm), our European correspondent informed us that the UK press kit lists power at 77 hp (without ram air), and 80 hp (with ram air). At least this provides us with a ballpark figure, assuming that the model is the same for both markets.
Ingesting air from the front of the fairing is a ram air duct that feeds the airbox via intake funnels in two different lengths of 40 and 60mm. The engine’s large oversquare bore allows for more valve area with 22.1mm intake and 19mm exhaust valves. Feeding the engine are 34mm throttle bodies with Kawasaki’s latest Electronic Throttle Valves (ETV), allowing the high-spec ECU (rider aids are discussed below) to precisely control both the fuel to the injectors and the air entering the intake stream. The intake ports are cast with a super fine sand, resulting in smooth surfaces. The intake port area near the valves has been machined to create a very straight path into the combustion chambers to maximize airflow.
Ultra-lightweight cast-aluminum pistons have a molybdenum coating on the skirts for durability, while a reasonable 12.6:1 compression ratio ensures regular gasoline can be used (for reference, the 1990 model’s compression ratio was 12.1:1). Pistons slide in die-cast aluminum cylinders with an open deck design. The connecting rods have a carburizing treatment to help improve durability, while the crankshaft’s light flywheel mass contributes to the engine’s quick-revving nature.