By May 12, 2011 Read More →

BMW M3’s four-cylinder engine

BMW M3 engine 1987After the production of the BMW M1 had stopped, the BMW CEO Eberhard Kuenheim commissioned a design for a successor. On one of his regular visits to Motorsport GmbH in Munich’s Preußenstraße he said, “Mr. Rosche, we need a sporty engine for the 3 Series.” Motorsport GmbH with its managing director of technical development Paul Rosche had demonstrated its expertise with the legendary 5 Series saloons driven by M engines as well as developing the Formula 1 turbo engine that powered Brazilian Nelson Piquet to win the World Championship in the Brabham BMW in 1983.

The new 3 Series engine had something in common with this: the crankcase. It originated from volume production and actually formed the basis for the two-litre engine with four cylinders. Four cylinders meant less weight and high torque, an ideal platform for a sports engine in the projected displacement class. Naturally enough, the series four-cylinder engine was much too tame for a sports engine. A comprehensive power boost was called for in order to turn the plucky daily workhorse into an athletic and sporty power unit. The BMW design engineers increased the displacement to 2.3 litres and applied a formulation that had already achieved significant successes over a period of many years: four-valve engineering.

There was also another reason for the decision to opt for a four-cylinder engine and not adopt the six-cylinder engine introduced in the BMW 3 Series. The longer crankshaft in the big engine started to vibrate much earlier than the shorter four-cylinder shaft. The design engineers therefore designed the crankshaft drive of the BMW M3 with sufficient torsional stability to achieve 10,000 revolutions a minute and more. By comparison with the four-cylinder engine installed in the series vehicles, this represented an increase of more than 60 percent. The rated speed for the road version of the BMW M3 was still significantly below the critical range at 6750 rpm and therefore offered sufficient scope for further developments.

Paul Rosche recalls: “We started work immediately. One advantage was that the big six-cylinder engine originally had the same cylinder gap as the four-cylinder engine. We therefore cut two combustion chambers off the four-cylinder head of the M88 and bolted a panel over the hole on the rear side.” This meant that the new four-cylinder engine had a second forebear. Paul Rosche: “Whether you believe it or not – we had created an outstanding four-cylinder engine for the 3 Series within the space of two weeks. The key data revealed a sports car that would punch way above its class; 200 hp ans 240 Nm would sprint the M3 from zero to hundred in 6,7 seconds and provide a top speed of 235 km/h.

Type

  • Straight 4-cylinder

Capacity

  • 2302cc

Power

  • 147 kW (200hp) / 6750rpm

Torque

  • 240 Nm / 4750rpm