[1] This direct-drive aero-engine is unusual in two respects: it is very oversquare with a bore:stroke ratio of 1.295:1, and it has a side-valve (flathead) valvetrain.
The designer determined that since maximum continuous power output (65.3 kW[2]) was to be developed at only 2800 rpm, the extra weight and complexity of overhead valves (OHV) would be superfluous.
The resulting engine is compact and lightweight, with a dry weight of 58 kg (128 lb),[2] and a maximum power-to-weight ratio of 1.09 kW/kg (wet; coolant fluids weigh 5 kg (11 lb)[2]).
The engine has port injection, a dry sump lubrication system, and dual ignition.
With the aid of funding from the Belgian government,[3] D-Motor has developed a derivative 4-litre flat-six engine, the D-Motor LF39, which is claimed to produce 125 PS (92 kW) and to have dry weight of 78 kg (172 lb).