The Lamborghini V12 engine was virtually unchanged from the engine used in the 400 GT 2+2. This engine, based on Giotto Bizzarrini's original design for Lamborghini, had an aluminum alloy crankcase with cast-iron cylinder liners, aluminum pistons, 24 valves (two per cylinder) and two chain-driven overhead camshafts per bank. Cylinder bore was 82 mm and stroke was 62 mm. Compression ratio on series I engines was 9.5:1, which increased to 10.7:1 in the series II/II engines. Six Weber 40DCOE side-draft carburetors were equipped, along with a single distributor for ignition. Wet sump lubrication was used, with an oil capacity of . The weight of the engine alone was , or including the transmission. Power output of series I cars was stated as 325 hp at 7,200 rpm, while Series II/III cars produced a stated 350 hp at 7,500 rpm.