The Missile Science Behind Two-Stroke Engines

As PopMech‘s autos editor, I obviously consider myself an automotive guy. But when it comes to two wheels, the capabilities of modern motorcycles amaze me. We now have road-legal bikes producing over 200 horsepower – from a 1-liter engine – rolling through showrooms with anti-lock brakes, wheel control and even speed-sensitive traction control. the inclination. While these modern two-wheelers are stunning, things were different when two-stroke engines were in their early development and drum brakes were the norm.

It all started in the 1960s with the MZ Racing Team. Originally known as Motorrad und Zweiradwerk, which translates to “motorcycle and two-wheeler factory,” the German motorcycle manufacturer took their machines to the racetrack to huge success. These victories and triumphs are due to a German missile specialist: Walter Kaaden.

During World War II, Kaaden was a Nazi engineer who reportedly worked on the V-1 and V-2 rockets. Like many Germans at the time, he was not a Nazi by choice and was forced to join the party after Hitler entered the war. After the defeat of the Axis, he sought to use his knowledge for more peaceful purposes in motorcycles. His understanding of gas flow and rocket resonance allowed him to design an expansion chamber to optimize a motorcycle’s power and efficiency. Using an oscilloscope, Kaaden made adjustments to the bulbous exhaust piece that would lead to big compression gains, which translated to more power.

Kaaden accomplished this by harnessing the sound waves and exhaust gases emitted from the engine itself. After each combustion stroke, the expansion chamber would suck the clean cylinder of spent exhaust gases. Then, before the next combustion cycle, it would draw in cool air and return it to the cylinder for more power. Kaaden basically understood forced induction before supercharging and turbocharging. The end result was a two-stroke engine that produced up to 200 horsepower per liter, nearly double what was previously possible – the most powerful engine ever produced at the time.

The engine of a DKW 350 RM.

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In fact, Kaaden’s engines were so successful that Soichiro Honda (the man behind Honda Motor Company) tried to outdo him using four-stroke technology. To rival the sheer power of Kaaden’s machines, Honda engineers attacked the problem with more pistons while maintaining similar displacement. The culmination of their work was the 1966 RC166 motorcycle, which used a 250cc twin-cylinder engine that produced 280 horsepower per liter and revved up to 20,000 rpm, one of the most powerful engines in the world.

However, after Kaaden’s success on the circuit with famed motorcycle racer Ernst Degner, the duo parted ways for the 1962 season. Degner ended up stabbing his longtime compatriot by selling Kaaden’s two-stroke secrets to Suzuki, which was struggling to build an engine that would go along with its riders. Degner won the 50cc World Championship, single-handedly putting Suzuki back on the map. Kaaden’s MZ machines had won races, but the Suzuki was the first two-stroke to win a world championship. After other manufacturers caught wind of what the Japanese motorcycle maker had “discovered,” the rest was history. Kawasaki would go on to use a carbon copy of Kaaden’s engine in their KR250s and 350s to win eight world titles.

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Emissions regulations eventually prevented the widespread use of two-stroke engines, notorious for belching out tons of smoke and pollution. However, now that we have direct-injected two-strokes, which can actually run cleaner than modern four-strokes, we could see a resurgence in Kaaden’s machines. Manufacturers could reap the traditional benefits of lighter, more affordable and now even more efficient two-stroke engines.

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