Both 300 SEb and 300 SEL were fitted with 2,966 cc M189 engine. The engine was an updated version of M186, originally developed in 1951 for Type 300 "Adenauer", with Bosch mechanical fuel-injection system that calibrated the optimal fuel mixture automatically based on throttle pedal position and movement, engine speed, atmospheric pressure, water temperature, and driving conditions. The engine's output was at 5,400 rpm, and 300 SEb and 300 SEL could accelerate to in 12 seconds and reach the top speed of ( with automatic transmission).