Tech watch: Kawasaki's greener screamer

Since the introduction of Euro5 emissions limits in 2020, we’ve seen an exodus of much-loved bikes from the market as their makers struggle to justify the investment needed to develop and comply with regs.

High-revving four-cylinder sportsbikes have been the biggest casualties, but as heroes like the Honda CBR600RR and Yamaha R6 disappeared from sale, Kawasaki have leapt in with a new screaming 400cc inline four in the form of the
ZX-4RR which is set to arrive in the UK in September at £8699.

So how has Kawasaki managed to launch an emissions-compliant 16,000rpm four in the teeth of legislation that seems tailormade to target exactly such designs?

Euro5 is bad news for screamers thanks to limits on hydrocarbon emissions. They were slashed from 170mg/km under Euro4 to 100mg/km in Euro5, but there’s also a new limit of 68mg/km for ‘non-methane hydrocarbons’ (NMHC).

This was the big challenge to high-revving bikes, which need lots of valve overlap – when the inlet valves open before the exhausts have closed to maximise the fresh mixture entering the cylinder – to work at high speed…