Inline six-cylinder engines are one of the pillars of BMW. They are a fundamental element of the manufacturer's DNA. BMW would be inconceivable without these engines. And they are not just a part of the brand's recent history: their origins go back to the time before the Second World War, when things were not going well in Munich and the situation was certainly not the best.

The BMW 326, the first model to position itself at the top of the market then occupied by Mercedes with innovative technical solutions and an engine that was to make history, got the company back on its feet: the M326. Here is its story ...

Six for history

To compete with Stuttgart, it was not enough to raise the bar in terms of quality and technology. Good performance and driving pleasure also had to be guaranteed. So the Munich engineers took the 1.9-litre from the 319, modified it in many ways, enlarged the bore and stroke and increased the displacement from 1,911 to 1,971 cc.

Equipped with a rocker arm control with overhead valves and two Solex carburettors, it initially produced 50 PS. Just enough for a car of the time that wanted to combine sportiness and elegance. But that was just the beginning of a story of ever-increasing performance. With the first tuning - for the BMW 320 and 321 - the output dropped to 45 PS.

BMW 326

BMW 326

With the 327, the Bavarian engineers began to further improve the M326 engine, increasing its output to 55 PS in 1937 by changing the compression ratio from the original 6:1 to 6.3:1. This was nothing special, but it was a start: the new in-line six-cylinder was an engine that could do even more.

BMW 328 Motor

The "more" came with the BMW 328, which was presented at the Nürburgring in 1936 and was a sporty further development of the 326 presented a few months earlier. A car that was developed in record time and on a low budget and was also created for participation in competitions.

An M326 engine with an increased output of 80 PS, an aluminium cylinder head, hemispherical combustion chamber and cross-flow valves were installed. The latter solution offered a not inconsiderable advantage: the unusual arrangement of the connecting rods made it possible to position the carburettors vertically. Better for the air supply.

BMW 327

BMW 327

BMW 328

BMW 328

In the racing versions, the power output was between 100 and 110 PS, a limit set not by the mechanics but by the petrol, which at that time reached a maximum of 80 octane and limited the compression ratio to 9.5:1. There would have been a risk of burning the pistons.

Thanks to the use of special fuels, the BMW engineers were able to increase the performance of the M326 even further, bringing it up to 136 PS. There were further developments, such as the introduction of the fuel injection system with three valves instead of carburettors in 1941. 

Second British life

At the end of the Second World War, BMW began supplying the M326 engine to Bristol (how voluntarily is debatable), a British car manufacturer founded in 1947 by the Bristol Aeroplane Company, a company specialising in aircraft. Just like BMW in the early years.

Bristol 450

Bristol 450

The German engine was modified by British engineers and used for the Bristol 400 family (which was very similar to the BMW 326 and its derivatives). Power was increased to 155 PS in the Bristol 450, a very special racing car that reached a top speed of 146 mph (235 km/h).

Gallery: BMW's M326 engine and its cars