The Accord's 2.4-liter DOHC i-VTEC PZEV-compliant engine has two modes of exhaust valve operation. Below 2500 rpm, only one exhaust valve operates, creating a strong rotational flow in the exhaust gases that creates a "thermal reactor" effect to reduce hydrocarbon emissions. Above 2500 rpm where exhaust flow increases, a hydraulically actuated pin locks the rockers for both exhaust valves together so they operate in unison, following a single cam profile.
