BMW M73 Engine (1994-02)

Available from 1994, the M73 was a 5.4-litre V12 petrol engine that was first used in the E38 750iL. Based on the 5.0-litre M70 V12 engine which it replaced, the 5379 cc M73 engine had a 60-degree ‘V’ angle, an 85.0 mm bore and a 79.0 mm stroke. Furthermore, the M73 was mated to the ZF 5HP30 (BMW’s A5S 560Z) five-speed automatic transmission.

The M73 Technical Update (M73TU) engine was released in late 1998 for the 1999 ‘model year’ – it introduced an electrically-heated catalyst to satisfy US LEV and EU3 emissions standards. In 1999, the M73TUB54 won the ‘Above 4 Litre’ category in the International Engine of the Year awards.

The M73 was superseded by BMW’s N73 V12 engine.

The M73 block had an aluminium/silicon alloy (Alusil) block, a die-cast aluminium cylinder head with a cross-flow design, a single overhead camshaft (per cylinder bank, chain-driven), a forged steel crankshaft, sintered connecting rods, two valves per cylinder and knock sensors that were mounted to the cylinder heads. The M73 engine also introduced a new EML IIIs electronic throttle control system which was produced by Siemens.

The camshafts were produced by fusing sintered metal camshaft lobes to the hollow metal shaft and each camshaft had seven split bearings. For a more aggressive camshaft profile and reduced friction, roller rocker arms were used to actuate the valves. Unlike the M70 engine which had sodium-filled exhaust valves, the M73 engine had solid steel exhaust valves.

The M73 engine had aluminium alloy pistons which were coated with a 0.1 mm metal film; the pistons for the left and right cylinder banks, however, differed to compensate for the wrist pin offset and asymmetrical combustion chamber.

The M73 engine had two separate Bosch 5.2 Motronic Control Systems (one for each cylinder bank) and operated at a compression ratio of 10.0:1. The firing order was 1-7-5-11-3-9-6-12-2-8-4-10.