Four factory 906s received an air-cooled eight-cylinder boxer engine of the type 771, which was already used in the 904/8. The engine had a displacement of 2.2 liters with a compression of 10.2: 1 and vertical shafts that drove the two overhead camshafts per cylinder bank. The maximum output was 198 kW (270 hp) at 8600 rpm. All vehicles were equipped with a five-speed manual transmission of the type 906 and a ZF limited-slip differential . The gear ratios could be exchanged as required without removing the gear.