How BMW’s M115 four-cylinder became F1 world champion

The engine palette at BMW in the late fifties is fairly well-arranged. Two-cylinder boxers from motorcycles are used for the small Isetta and the compact BMW 700. At the top of the range, BMW has a V8 with a choice of displacement of 2.6 or 3.2 liters. There is also a six-in-line that is used in the 501 with a capacity of 2.0 and 2.1 liters. However, that six-cylinder actually dates from 1933 and, despite the necessary adjustments, is slowly approaching its best before date.
For the future, the development department is assigned to develop a compact four-cylinder; a displacement of 1.3 liters should be enough. In those days, driver cum engineer Baron Alex von Falkenhausen held sway in the engine department, and in his opinion a 1.3 liter is on the small side for what BMW needs in the future. He manages to convince the management that it makes more sense to develop a slightly larger engine, namely a 1.5 liter with the possibility to grow to two liters. Thus, Von Falkenhausen, assisted by sorcerer’s apprentice Paul Rosche, gets to work.

Initially, there will be experiments with four-cylinder engines based on the large aluminum V8. Both a four-in-line, derived from one of the cylinder banks of the V8, and a V4 are tried. In the end, preference is given to the inline engine. Initially, an aluminum engine is provided, with cast steel cylinder liners. However, that idea is considered too expensive. From a blank sheet of paper, a cast iron four-cylinder is then developed with a crankshaft bearing five times and a single overhead camshaft. This engine, with a displacement of 1.5 liters and a single carburetor, is internally designated M115 at BMW. The M115 makes its 80 hp debut in September 1962 during the IAA in Frankfurt under the hood of the all-new BMW 1500, also known as the Neue Klasse (new class).

BMW 2002 Ti

Variations on the M115 theme soon follow. In 1963, for example, the M118, which powers the BMW 1800 with a capacity of 1.8 liters and 90 hp, and in 1964 the M116 with 1.6 liters of displacement. A two-litre version (M05) appears in 1965 in the BMW 2000 Coupé. And when the New Class is replaced by the first 5-series in 1972, the four-cylinder provides the drive for the 518 and 520. The engine with different displacements is also used in the 02-series. In addition to versions with single carburetor, there are also variants with double copies, which increase the power to 120 hp. The performance is even higher when a Kugelfischer injection system is allowed to show its tricks in 1972: 130 hp in the 2000 and 2002 tii. A year later, a turbo in the 2002 turbo ensures that the power increases further to 170 hp. When the first 3-series (E21) appears in the same year, the four-cylinder is also quickly a familiar value in that car. This will remain so until the end of the eighties in both the 5-series (E28) and the 3-series (E30).

The sports department also sees potential in the four-cylinder. Equipped with a cylinder head with sixteen valves and injection, the engine is used in Formula 2 from 1966, initially with 260 hp at 8,500 rpm. The wealth increases over the years. The block is also a good starting point for touring car racing. Powers of more than 300 hp are no exception. With a shortened cylinder head of the six-cylinder M88 engine (used in the M1) and a cylinder capacity of 2.3 liters (later even 2.5), we also find the engine in the BMW M3 at the end of the eighties. The bike is now called S14 and manages to win one championship after another. The power ratings for the production versions range from 195 to 238 hp. Impressive? Yes. But … it’s child’s play compared to the performance the engine delivers when Paul Rosche takes it for Formula 1 in the early 1980s.

Fitted with an executioner of a turbo, the engine debuts as an M12 with a displacement of 1.5 liters in 1982 in the back of the Brabham BT50. That power grew a year later in the Brabham BT52 to 640 hp (in qualifying trim even to 850 hp) and Nelson Piquet conquers the drivers’ championship with it. In the following years, the power increases to 1,100 hp in Formula 1 (including Arrows and Benetton) and no less than 1,400 hp in the American IMSA class. Incidentally, the powers above 1,000 hp are theoretical calculations. There is no engine test bench that can withstand the violence of those days. Championships are not forthcoming, the mechanics suffer a lot and too often the Brabhams are standing along the track with a blown engine.

This article originally appeared in AutoWeek Classics issue 4 of 2016.