a hydraulically controlled multi-plate clutch to apportion drive between front and rear axles, whereas the manual transmission variants utilize a Torsen type 1 Torque Sensing center differential. The rear axle final drive unit contains a Torsen type 1 Torque Sensing differential, instead of the more common hypoid open differential. Engines Both available engines used a Bosch Motronic fully electronic engine control unit (ECU), with cylinder bank selective knock control, dual-barrel throttle valve, lambda mixture control via intake air volume metering and exhaust gas temperature sensor, and required unleaded petrol. Fuel was delivered to the combustion chambers via eight intake manifold-sited electronic fuel injectors, fed from two common fuel rails (one per cylinder bank), and were sequentially 'fired' or activated in accordance with the engine's firing order. Whilst the 3.6 V8 was able to use 95 RON (91 AKI) fuel, for the 4.2 V8, the more expensive 98 RON (93 AKI) 'SuperPlus' unleaded was required in order to achieve the quoted power output. The usage of 95 RON in the 4.2 V8 resulted in a lower power output, as well as increased fuel consumption. At the initial launch of the Audi V8, the only offering was the 3.6-litre powerplant, which displaced . This V8 engine was DIN-rated with a maximum motive power output of at 5,800 revolutions per minute (rpm), and generated a torque turning force of at 4,000 rpm. In August 1991, Audi introduced a 4.2-litre engine, displacing , to complement the choice of the existing 3.6-litre V8. This shared many components from the 3.6 V8, and the 4.2 unit was identical to the optional V8 used in the Audi S4 (aka Ur-S4), sharing the same rated outputs and ABH identification code. Like the 3.6 V8 model, the existing four-speed automatic gearbox remained available. However, a new six-speed manual gearbox replaced the five-speed manual. This powerplant is identified by chrome 'V8' badges on the front grille and at trunk lid, where in some cars also '4.2 quattro' badge is present. Details and performance Transmissions A choice of transmissions were offered. A ZF Friedrichshafen-sourced four-speed 4HP24A automatic transmission with a torque converter was available throughout the V8 production run. Automatic transmission has three modes: "S" – Sport; "E" – Economic and "M" – Manual operation. Sport mode is changing gears at higher rpm than Economic; Manual mode allows driver to choose gears using the lever. There were also two manual transmission