The BMW M73 is a naturally-aspirated,

SOHC An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

, V12

petrol engine A petrol engine (gasoline engine in American English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as ' ...

which replaced the

BMW M70 The BMW M70 is a naturally-aspirated, SOHC, V12 petrol engine, which was BMW's first production V12 and was produced from 1987 to 1996. The BMW S70/2 engine, largely unrelated to the M70 and S70B56 engines, is a naturally-aspirated, DOHC, V12 ...

and was produced from 1993 to 2002. It was used in the BMW E38 7 Series, E31 8 Series and Rolls-Royce Silver Seraph.

Design

Compared with its M70 predecessor, the M73 features an updated roller-rocker valve-train and an increased displacement, due to a bore increase of ending with a cylinder bore of 85mm and a stroke increase of to have a final piston stroke of 79mm. While most other engines in the BMW range had switched to dual overhead camshafts with four valves per cylinder, the M73 used a

single overhead camshaft An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

and with two valves per cylinder. However, BMW engineers did create a prototype four-valve per cylinder V12, called the M72, which developed and of torque. However, this 48-valve engine did not fulfill the comfort demands of the large sedan class in all respects and, as a result, did not go into production. Some versions of the engine have two separate Bosch Motronic

engine control unit An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by ...

s, while others use a single Siemens ECU. The hydrogen versions of the engine feature a

\lambda \ge 3.0

lean burn concept, which allows quality torque control similar to a Diesel engine (i. e. no engine throttling). Due to the lower LHV of a hydrogen-air mixture, and the fact that the engine was designed as a Bi-Fuel (petrol and hydrogen) engine, the power output is reduced by 38 per cent compared to the petrol only version of the engine.

Models

M73B54

Applications: * 1994-1998 E38 750i/750iL/L7 * 1994-1999 E31 850Ci

M73TUB54

Due to more stringent emissions standards, the 1999 model year marked the addition of an electronically heated catalyst, variable MAP thermostat, and water cooled alternator. Applications: * 1998-2001 E38 750i/750iL/L7/hL * 1998 Cardi Curara * 1999-2002 Rolls-Royce Silver Seraph * 2009–2010 Symbol Design Lavazza GTX * 2013 Monte Carlo Automobile Rascasse

M72B54 prototype

In 1989, as part of a feasibility study, BMW's engine development department produced a four-valve version of its V12 engine. Only one engine was produced, having an up-sized variant of the M70B50 engine called the M72B54. Bore and stroke was increased to 85mm and 79mm and the total displacement of 5.4L was achieved, matching the values of the standard M73 engine. The power and torque both increased to and respectively.

Awards

* 1999

International Engine of the Year The International Engine of the Year is an annual competition for automotive industry internal combustion engines and electric motors, judged by a panel of automobile journalists from around the world. It is organised by UKi Media & Events' Automot ...

- Best Above 4.0 Litre category winner