The V4 engine was retained for the Evo, producing 720 PS (530 kW; 710 hp) without fuel flow restrictions. As the amount of recovered energy that could be used was increased from 6.37 MJ (1.77 kWh) for Circuit de Spa-Francorchamps to 8.49 megajoules (2.36 kWh), the output of the electric motors was increased from 400 to 440 PS (294 to 324 kW; 395 to 434 hp). By removing air conditioning, windscreen wipers, headlights and other electrical devices, the car's weight was reduced by 39 kg (86 lb); it weighed at 849 kg (1,872 lb) dry and 888 kg (1,958 lb) with driver ballast. Extensive aerodynamic upgrades to the 919 Evo increased downforce by 53% and increased aerodynamic efficiency by 66%, compared to the 919 Hybrid's 2017 6 Hours of Spa-Francorchamps qualifying specifications. These upgrades consist of the inclusion of an active drag-reduction system, an enlarged rear wing, a wider front diffuser and fixed-height side skirts