The Rise and Fall of Two-Stroke Car Engines: A Historical Overview
We’ve seen many engine configurations come and go, with some being more noteworthy than others and some being just outrageous. Honda attempted to modify the shapes of the pistons used in its engine, but although this technology didn’t pan out as hoped, it was an interesting idea. At one point, Chrysler toyed with the idea of turbine engines, while Ford ditched engines entirely for nuclear reactors.
One engine configuration had merit and was once touted as a revolution in engine technology. That was the two-stroke engine, and while it’s most commonly associated with motorcycles, these were the go-to for some automakers and, at the time, were a promising prospect.
The Rise Of The Two-Stroke Engine
The advent of the two-stroke engine, or better yet, an engine with a two-stroke combustion cycle, dates back more than 200 years. The first appearance of a two-stroke engine was around 1879 when a German inventor named Carl Benz (yes, Benz as in Mercedes-Benz) invented a stationary one-cylinder two-stroke gasoline engine that ran for the first time on New Year’s Eve 1879.
While a single-cylinder engine might be weird, at one point, even Cosworth built one. Following significant commercial success with this new engine, Benz – widely considered the father of the automobile – pursued his dream of a lightweight car powered by a gasoline engine where the chassis and engine were formed as a single unit. By 1886, Benz filed a patent for the first vehicle powered by a gas engine, which took the form of a three-wheeled motor car.
The first commercial appearance of the two-stroke engine with cylinder compression is believed to be the creation of a Scottish engineer, Dugald Clerk, who patented his design in 1881. The defining aspects of the two-stroke engine were, in comparison to conventional four-stroke engines, its mechanical simplicity, power-to-weight ratios, and weight. The two-stroke engine and engine technology as a whole would continue to evolve, but the two-stroke engine’s mainstream adoption would only start in the 1970s.
Early adopters
One of the earliest examples of a two-stroke engine in an automobile was the Aero Type 30, which was powered by a twin-cylinder two-stroke engine that powered the front wheels and allowed it to reach a top speed of 65 mph. It would be the Czechoslovakian automobile company that produced more than 8,000 examples before production ceased in 1947. Another manufacturer to be one of the early adopters of the two-stroke engine was Berkeley Cars. This Bedfordshire-based automotive company produced microcars that were powered by motorcycle engines.
In 1956, Berkeley introduced the Berkeley Sports SA322, which employed a transversely mounted twin-cylinder two-stroke engine that generated 15 hp, powering the front wheels. This might not sound like much, especially considering that other cars with two-stroke engines produced more than double that. Still, it was housed in a microcar that weighed only 605 lbs. It also reportedly had commendable handling characteristics, and the model that followed improved on all its performance metrics, with the final incarnation of this microcar wielding an output of 30 hp.
In 1958, Auto Union GmbH began production on the Auto Union 100, a luxury compact car. At its core was a two-stroke inline three-cylinder engine with a displacement of 981cc that mustered a total output of 43 hp. Interestingly, this car would be used in various motorsport disciplines, garnering massive success in endeavors like the 1961 South African National Rally Championship.
How The Two-Stroke Engine Works
To understand how the stroke engine works, we first have to talk about the combustion cycle. A four-stroke engine, which is the common engine configuration in modern cars, works in four distinct stages: the intake, compression, combustion, and power stroke. The term “stroke” refers to the movement of the piston up and down, with each phase in a four-stroke engine representing one stroke up and down. In this configuration, spark plugs fire every other revolution, and power is generated after four strokes of the piston.
In contrast, a two-stroke engine’s combustion cycle features the same combustion cycle as a four-stroke engine, but its combustion cycle is in the span of two strokes of the piston instead of four. This is done by combining the intake and exhaust phases with the compression and power stroke stages. On the first stroke of the piston, it is driven upwards by compressing an air-fuel mixture that is drawn into the combustion chamber through the intake port, which closes along with the exhaust port as the piston reaches the top of its upward cycle (also known as top dead center).
After the air-fuel mixture is ignited, the piston is driven downwards, which generates power. As the piston is driven downwards, the exhaust port opens and allows the gases to be fed into the exhaust manifold. At the same time, the transfer port allows another portion of the air-fuel mixture to enter the crankcase to flow into the cylinder. Once the piston reaches the lowest point in its stroke (known as bottom dead center), the process starts over.
The advantages and drawbacks of the two-stroke engine
Compared to the four-stroke engine, two-stroke engines typically have the advantage of having fewer moving parts, making them more compact and therefore taking up less space. Additionally, these engines were initially cheaper to produce, which increased their appeal in comparison to four-stroke engines. The compact nature of two-stroke engines meant that these were typically lighter power units and, because of this, possessed a better power-to-weight ratio than the conventional four-stroke engine.
Additionally, these engines had the potential to generate twice as much power as a four-stroke engine of the same size, due to their two-stroke design allowing for more power stroke phases. However, while the benefits of the two-stroke made it an appealing option, these engines were notorious for their less-than-ideal fuel efficiency in comparison to four-stroke engines, which was compounded by the fact that these engines also suffered from high oil consumption as a result of high operating temperatures.
The Cars Powered By Two-Stroke Engines
It was during the 1960s that larger and more prolific automakers began implementing the two-stroke engine in their cars. In 1966, Daihatsu introduced the Daihatsu Fellow, a compact saloon powered by a water-cooled 356 cc two-stroke twin-cylinder engine. This engine offered roughly 23 hp exclusively to the rear wheels in a compact car weighing only 1,135 lbs. Interestingly, this bite-sized saloon was also configured as a pickup truck and van.
One of the better-looking cars to employ a two-stroke engine was the Malzoni GT, which was a road-going car based on a race car, that utilized the shortened wheelbase of the DKW Sonerklasse and was powered by a three-cylinder two-stroke engine. The Malzoni GT would see significant success in motorsport. Mazda was another name that tried its hand at the two-stroke engine, with the Mazda Chantez, which was a kei car introduced in the early 1970s. Although it wasn’t as sporty as another kei car with supercar styling, it featured a 359 cc twin-cylinder two-stroke engine that surprisingly offered 35 hp and could propel this 1,080 lb kei car to a top speed of 71 mph.
In 1969, Subaru began production of the Subaru R-2, a petite kei car powered by a 356 cc air-cooled two-stroke engine shared with the Subaru Sambar, a commercial truck. The R-2, in contrast, was a tiny car characterized by its rounded headlights. While the entry-level model offered approximately 25 hp, a sportier performance version called the R-2 SS had dual exhaust, an increased compression ratio, and a higher output. At one point, even Ford tried to take a swing at the two-stroke engine.
The Fall Of The Two-Stroke Engine
While there was some merit to the use of two-stroke engines in cars, it wasn’t good enough to compete with the feasibility of four-stroke engines. In the end, the two-stroke engine would be relegated to motorcycles as the four-stroke became the mainstream configuration. What caused the two-stroke’s reputation to sour was the poor fuel efficiency and, more importantly, the higher emissions produced compared to four-stroke engines.
The increasingly stringent emissions regulations would be the final and largest nail in the two-stroke engine’s coffin. While the two-stroke engine suffered, four-stroke engine technology was advancing. Today, we are on the cusp of a new six-stroke engine configuration by Porsche, characterized by six piston strokes for seven cycles, one of the exciting engines coming in the next few years. What was touted as a revolution in engine technology, the two-stroke engine is now remembered as a disappointment in the history of the automobile.
Sources: ResearchGate, Mercedes-Benz