BYD recently developed a brand new 1.5 Naturally Aspirated(NA) engine dedicated to its Dual Mode-intelligent(DM-i) plug-in hybrid architecture. This engine can reach a peak of 43% brake thermal efficiency. Combined with Electric Hybrid System(EHS), the full architecture can achieve low fuel consumption at various vehicle speeds, while maintaining fast accelerations. To reach such high thermal efficiency, the technological choice consisted in the association of: high compression ratio of 15.5, long stroke, Atkinson cycle, high tumble port, cooled EGR and high energy ignition. High compression ratio led to the increase of knock and pre-ignition tendency, which was suppressed by EGR and piston cooling jets. A lot of work was also done on the software side to optimize knock and pre-ignition control. The thermal management was completely redesigned. The use of electronic water pump, associated with two thermostats (one electronic and one traditional wax type) made it possible to implement split cooling and gradient control of coolant temperature map. Associated with intelligent control of thermal needs under all working conditions, the benefits were: faster engine warm-up, improved fuel economy and emissions reduction. To push the thermal efficiency even higher, friction was reduced to its minimum through different measures: 0W-20 oil, low tension piston ring, piston DLC coating, two-stage variable displacement oil pump and electrification of the accessories. With the combination of these technologies, and further optimization, the new dedicated 1.5NA high-efficiency engine achieved top level thermal efficiency in its class. Applying this engine to the DM-i plug-in hybrid architecture, the vehicle can achieve a charge-sustaining fuel consumption of 3.8 L per 100 kilometers in the WLTC cycle.