,

The Powerful BMW M73: the V12 engine used at Rolls Roce

In the world of classic cars, few engines capture the essence of luxury performance like the BMW M73. With its distinctive roar and mammoth power, the M73 has earned a place of honor in automotive engineering history. In this article, we’ll explore this iconic V12 engine in depth, from its groundbreaking design to its applications in some of BMW and Rolls-Royce’s most iconic vehicles.

Foto: ©BMW

Ingenious design

The BMW M73 is a naturally aspirated V12 gasoline engine with an overhead camshaft and two valves per cylinder. Its development marked a significant evolution over its predecessor, the M70, by featuring an updated roller valve train and an increase in displacement. With a cylinder bore increased by 1 mm and stroke increased by 4 mm, the M73 achieves a final displacement of 5,379 cc.

Although other engines in the BMW range had adopted the twin-overhead camshaft configuration with four valves per cylinder, the M73 remained true to a single overhead camshaft with two valves per cylinder. However, BMW engineers explored the possibility of a four-valve-per-cylinder V12 engine, known as the M72, which achieved a power output of 265 kW and torque of 530 Nm. Despite its impressive performance, this 48-valve engine did not make it to series production due to certain limitations in terms of comfort for the luxury sedan class.

Some versions of the M73 engine use two Bosch Motronic engine control units, while others employ a single Siemens unit. In addition, the hydrogen variants of the engine feature a clean combustion concept with a very high air-fuel ratio, allowing precise torque control without the need for engine throttling.

Models and Applications

The BMW M73 engine has been used in a number of flagship vehicles over the years. Below are some of the variants and their most prominent applications:

M73B54

VERSIONDisplacementPOWERTORQUE ENGINEYEAR
M73B545,379 cc240 kW490 Nm1994

Applications::

  • BMW E38 750i/750iL/L7 (1994-1998)
  • BMW E31 850Ci (1994-1999)

M73TUB54

This model, introduced in 1998, incorporated improvements to meet stricter emissions standards, such as an electronic heated catalytic converter, a variable absolute pressure thermostat and a water-cooled alternator.

Applications:

  • BMW E38 750i/750iL/L7/hL (1998-2001)
  • Cardi Curara (1998)
  • Rolls-Royce Silver Seraph (1999-2002)
  • Symbol Design Lavazza GTX (2009-2010)
  • Monte Carlo Automobile Rascasse (2013)

M73 (Hidrógeno)

VersiOnPOWERTORQUE ENGINEYEAR
Hydrogen150 kW300 Nm2001

This version of the M73 engine, adapted to run on hydrogen, has reduced power compared to the gasoline version due to the characteristics of the alternative fuel.

Prototype M72B54

As part of a feasibility study in 1989, BMW’s engine development department produced a four-valve version of its V12 engine. This prototype, known as M72B54, featured a displacement of 5.4 liters and achieved a power output of 265 kW and torque of 530 Nm. However, this 48-valve engine never made it to series production.

Recognitions and Awards

The BMW M73 received the prestigious “International Engine of the Year” award in the Best Engine over 4.0 Liter category in 1999, highlighting its excellence in performance and technology.

In short, the BMW M73 engine is a masterpiece of automotive engineering, combining power, refinement and reliability in one impressive package. Its legacy lives on in some of the most iconic BMW and Rolls-Royce vehicles, leaving an indelible mark on the history of internal combustion engines.