BMW M73

BMW M73 engine
BMW M73 engine
Overview
Manufacturer	BMW
Production	1993–2002
Layout
Configuration	60° V12
Displacement	5.4 L (5,379 cc)
Cylinder bore	85 mm (3.35 in)
Piston stroke	79 mm (3.11 in)
Valvetrain	SOHC
Valvetrain drive system	Chain
Combustion
Fuel type	Petrol 95 RON; Hydrogen;
Chronology
Predecessor	BMW M70
Successor	BMW N73

Last updated January 27, 2025

The BMW M73 is a naturally-aspirated, SOHC, V12 petrol engine which replaced the BMW M70 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 1 mm (0.04 in) ending with a cylinder bore of 85mm and a stroke increase of 4 mm (0.16 in) to have a final piston stroke of 79mm.^[1] 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 and with two valves per cylinder. However, BMW engineers did create a prototype four-valve per cylinder V12, called the M72, which developed 265 kW (360 PS; 355 hp) and 530 N⋅m (391 lb⋅ft) 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.^[2]

These engines have two separate Bosch Motronic engine control units,^[3] which are connected to a third single Siemens control unit, called EML.^[4] The engine utilizes four knock sensors mounted on the heads, a cam position sensor mounted on the right head and two crank sensors, one for each ECU. Throttle by wire is used. Similar to its predecessor, the M70, spark distributors are still present for each cylinder bank.

The hydrogen versions of the engine feature a $\lambda \geq 3.0$ lean burn concept,^[5] which allows quality torque control similar to a Diesel engine (i. e. no engine throttling).^[6] 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.^[5]

Models

Version	Displacement	Power	Torque	Year
M73B54	5,379 cc (328.2 cu in)	240 kW (322 hp) at 5,000 rpm	490 N⋅m (361 lb⋅ft) at 3,900 rpm	1994
M73TUB54		240 kW (322 hp) at 5,000 rpm	490 N⋅m (361 lb⋅ft) at 3,900 rpm	1998
M73 (Hydrogen)^[7]		150 kW (201 hp) at 5,800 rpm	300 N⋅m (221 lb⋅ft) at 3000/min	2001

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,^[8] 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 Simbol 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 265 kW (355 hp) and 530 N⋅m (391 lb⋅ft) respectively.^[9]

Awards

1999 International Engine of the Year - Best Above 4.0 Litre category winner^[2]

Related Research Articles

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References

↑ "Information on M73 engines". www.bmwheaven.com. Retrieved 5 August 2017.
1 2 "BMW Super Bild Of The Day: 5.4 liter BMW V12". www.bmwblog.com. Archived from the original on January 18, 2013. Retrieved 5 August 2017.
↑ M73 Training Reference Manual (PDF). p. 2. Retrieved 10 April 2017.
↑ "E38 750iL Engine electrical system engine". www.realoem.com. Retrieved 10 April 2017.
1 2 Schüers, Andreas; Abel, Alois; Fickel, Hans-Christian; Preis, Michael; Artmann, Richard (February 2002). "Der Zwölfzylinder-Wasserstoffmotor im BMW 750hL". MTZ Motortechnische Zeitschrift. 63 (2): 100. doi:10.1007/BF03226613.
↑ Schüers, Andreas; Abel, Alois; Fickel, Hans-Christian; Preis, Michael; Artmann, Richard (February 2002). "Der Zwölfzylinder-Wasserstoffmotor im BMW 750hL". MTZ Motortechnische Zeitschrift. 63 (2): 103. doi:10.1007/BF03226613.
↑ Schüers, Andreas; Abel, Alois; Fickel, Hans-Christian; Preis, Michael; Artmann, Richard (February 2002). "Der Zwölfzylinder-Wasserstoffmotor im BMW 750hL". MTZ Motortechnische Zeitschrift. 63 (2): 99. doi:10.1007/BF03226613.
↑ "BMW M70, M72 and M73 V12 Engines". www.unixnerd.demon.co.uk. Archived from the original on 7 January 2016. Retrieved 5 August 2017.
↑ "BMW M72 twelve-cylinder four-valve engine". www.mwrench.com.