What is the engine displacement of Kawasaki Ninja ZX-4R?

Kawasaki Ninja ZX-4R is a 399cc liquid-cooled inline-4 DOHC cylinder motor that is capable of churning out some serious power. The unit is rated to produce 78 bhp of max power at a screaming 15,000 rpm and peak torque output of 37.6 Nm at 12,500 rpm. The motor comes mated to a slick 6-speed gearbox assisted by a slipper clutch and a quick shifter.