M73

The BMW M73 is a highly refined 5.4-liter, naturally aspirated V12 engine produced from 1996 to 2002. Serving as the successor to the original M70, it was engineered for flagship luxury models like the BMW E38 750i/750iL and E31 850Ci, prioritizing silky-smooth power delivery, abundant low-end torque, and reduced emissions.

• Updated Valvetrain: Unlike modern multi-valve engines, the M73 retained an SOHC 2-valve layout but upgraded to roller rocker arms (or rollenschlepphebel). This significantly reduced friction, minimized valve train noise, and improved longevity.
• Engine Management: It used the Motronic M5.2 (and later the M5.2.1) digital engine control, featuring dual electronic throttle bodies (Drive-by-Wire) and dual knock sensors.
• M73TU Update: In late 1998, BMW introduced the M73TU (Technical Update). This variant added a water-cooled alternator, ECU-controlled map thermostat, and electrically heated catalytic converters for better emissions compliance.
• Refined Exhaust and Emissions: The engine utilized secondary air injection to quickly heat up the catalysts during cold starts, heavily reducing warm-up emissions.