Car Features

Two-stroke engines have higher power-to-weight ratios than naturally aspirated four-stroke engines. Also, two-stroke engines have fewer moving parts and are lighter and cheaper to manufacture. Although the four-stroke eventually dominated, many car manufacturers used two-strokes in the 20th century.

First up, we’ll look at the fundamental differences between the two major engine types.

A two-stroke engine completes a power cycle with two strokes of the piston – one up and one down – in one revolution of the crankshaft, in contrast to a four-stroke engine that requires four strokes of the piston, in two crankshaft revolutions, to complete a power cycle. 

In the case of a basic two-stroke engine, as the piston moves from bottom dead centre to top dead centre, exhaust gas is forced out an exhaust port in the cylinder liner by the incoming air/fuel/oil mixture (known as scavenging), which is then compressed. The second, downward piston stroke is driven by combustion and expansion of the mixture, and, near bottom dead centre, the beginning of the scavenging gas flows.

Gas flows in a basic two-stroke engine rely on a sealed crankcase, because the piston’s power stroke compresses the air/fuel/oil mixture that has been sucked into the crankcase by the previous upward stroke of the piston. That compressed mixture is then forced up into the cylinder when the descending piston exposes a transfer port between crankcase and cylinder.

The power stroke of the piston exposes the exhaust port near the bottom of the power stroke, allowing most of the hot exhaust gas to escape. Residual exhaust gas is expelled (scavenged) by the incoming air/fuel/oil mixture.

In a basic two-stroke engine, lubricating oil for the crankshaft and connecting rod bearings, and for the piston, is pre-mixed with the fuel. Because the crankcase is sealed and pressurised by the descending piston it cannot have an oil-filled sump, as a four-stroke engine does.

This fuel/oil mixture is the weak link of the basic two-stroke, because it’s not the optimal way to lubricate the crank, rod bearings and the piston, and also it’s not an ideal combustion mixture, because the oil content gets burnt, increasing emissions.

Another issue is that when the engine is over-running – driven by the drivetrain as the vehicle rolls downhill – there is no incoming fuel/oil mixture, because the driver’s foot is no longer depressing the accelerator pedal, so the throttle is closed. That means there’s insufficient incoming oil to lubricate the rapidly-rotating engine parts.

Some car makers avoided that lubrication issue by having ‘freewheeling’ transmissions that disengaged the engine from the drive wheels when over-running, thus dropping engine speed to idle.

Another issue is that in a basic two-stroke engine, crankcase-transfer scavenging is imperfect, meaning that some of the compressing air/fuel/oil mixture passes out of the exhaust port, meaning a loss of engine efficiency.

Over the years, different engine makers have adopted various methods for overcoming the two-stroke’s flaws, as we’ll see.

Two-stroke engine history

The first commercial two-stroke engine involving cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881. However, unlike most later two-stroke engines, his had a separate cylinder that powered the scavenging cycle. The crankcase-scavenged engine is generally credited to Englishman Joseph Day.

The first practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott, who started producing twin-cylinder, water-cooled motorcycles in 1908. (Check out our Scott Motorcycle Brand story.)

A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab, German manufacturers DKW, Auto-Union and VEB Automobilwerke, and Polish manufacturers FSO and FSM.

Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution.  Eastern Bloc countries continued with two-stroke cars until around 1991, with the Trabant and Wartburg in East Germany.

Although the principles remained the same, the mechanical details of various two-stroke car engines differed: mainly because of the method of scavenging the cylinder – exchanging burnt exhaust for fresh mixture.

Since car makers abandoned the two-stroke engine, 21st-century types  are still used in some motorcycles and tools, such as snowmobiles and chain saws. Some have adopted innovations including intake reeds and rotary valves, pressured-oil lubrication and direct fuel injection – replacing fuel-oil premix. However, virtually all 20th century car two-strokes were basic designs, using piston-operated ports and premix.

Scavenging options

The earliest two-strokes used ‘cross-flow’ scavenging, in which design the inlet and exhaust ports were opposite each other, in the cylinder wall. Piston travel opened the exhaust port, which ‘bled’ exhaust gas through the port until atmospheric pressure was established, after which the piston exposed the inlet port and the air-fuel mixture transferring from the pressurised crankcase forced out the remaining exhaust gas, before compression began.

The downside of this design was that some of the incoming mixture went out the exhaust port, decreasing efficiency and increasing fuel consumption.

‘Loop’ scavenging was implemented to reduce or eliminate this waste, by directing the incoming charge away from the exhaust port, ‘looping’ the incoming charge up into the combustion chamber, before  descending towards the exhaust port.

Two-stroke deflector piston – Autocar-Andy Dingley

Most commonly that was done by the use of a shaped, ‘deflector’ piston, with a raised crown, but some designs relied on shaped porting and had a normal piston top.

Better than both these ‘solutions’ was a 1926 invention by Adolf Schnürle that positioned two inlet ports and a central exhaust port on the same side of the cylinder wall.

A single exhaust port was located in the cylinder wall, with its lower edge at the level of the piston crown at bottom dead centre. On either side of that exhaust, and angled away from it, were two transfer ports to deliver the fuel/oil mixture from the crankcase that had been pressurised by the descending lower face of the piston.

Schnuerle porting from above – Andy Dingley

The flow path of fresh charge entered the cylinder through these transfer ports, flowed across the piston crown to the cylinder wall, flowed up it, across the underside of the cylinder head and back down the exhaust-side cylinder wall to the exhaust port. 

This design achieved separation of the intake and exhaust flows as effectively as did the use of a piston deflector, while eliminating its undesirable characteristics: weight, expense and combustion chamber shape compromise. Compression ratios could be raised and piston heating was reduced by around a third.

With ‘Schnuerle’ (anglicised) or ‘Schnürle’ porting, the piston crown could have any profile – even a bowl – allowing for far better combustion chamber shape and flame path, giving better combustion, particularly at high speeds.

This variation on loop scavenging became widely adopted in Germany during the 1930s, but the Nazi regime wouldn’t allow its patented design to be implemented abroad, because it offered distinct advantages for the coming war effort – particularly in the case of military motorcycle engines.

After World War II, war reparations enforced on Germany ensured that this technology was available globally and became the norm in loop-scavenged engines, in conjunction with later German innovations, led by MZ-engineer Walter Kaaden’s exhaust system expansion chamber. (Check out Kaaden’s handiwork in our MZ Motorcycle Brand story.)

Different scavenging systems – Gordon Cornell

By far the most efficient scavenging method was ‘uniflow’ scavenging that became essential in diesel two-strokes, but that required a supercharger, a camshaft, poppet exhaust valves and a valve train, in addition to cylinder inlet ports. An alternative was a valveless, opposed-piston design, but both types of uniflow scavenging were too complex and costly for car makers who needed two-stroke, low-cost simplicity.

Yet another approach was the so-called split-single or twingle design, where an additional piston and cylinder were added, to compress the incoming air and fuel mixture. This second cylinder didn’t actually ‘fire’.

The additional cylinder design was used by DKW in its V4+2 engines, where the front two cylinders acted as compressors, but this was fitted only to the more expensive cars in its range.

Two-stroke car makers

Many car manufacturers have had a crack at making two-stroke cars, but only a few built their production around two-stroke cars for years. We’ve written them up as stand-alone brands in our Car Brands section: Aero, DKW, Lloyd, Saab, Trabant-Wartburg and the little-known Australian Zeta.

Saab 96 engine

The remainder of those who’ve dabbled in the two-stroke arena are listed below and there may be some from the early days of automotive development – 1890s-1910 – that we’ve missed or can’t get details about. For instance, we’ve heard about Cameron, Skene and Atlas two-strokes from the USA that didn’t last long in the market, but one that did was Elmore.

Elmore

1908 Elmore – Akrasia25

Elmore Manufacturing Company made automobiles and bicycles in Clyde, Ohio, from 1893 until 1912. Founded by Harmon Von Vechten Becker and his two sons, James and Burton, Elmore used a basic two-stroke engine design that let its advertising read: ‘The Car That Has No Valves’,

Initial models were powered by a horizontal, 5bhp-9bhp single-cylinder engine, but later models had two, three and four vertical cylinders, with outputs around 30bhp. These engines had simple cross-flow porting, but some loop scavenging was encouraged by a deflector ‘fin’ on each piston crown. The last, 70bhp developments saw the use of ‘stepped’ pistons and rotary valves.

1910 Elmore 36 – Hyman Ltd

By 1909, Elmore production capacity was around 1000 cars per year and that success caught the attention of one William (‘Billy’) C Durant, who had founded General Motors and was on a acquisition crusade, having consolidated 13 car companies and 10 parts-and-accessories manufacturers under the new holding company’s control by 1908.

In 1909, Durant’s GM bought Cadillac, Oakland and Elmore. By 1910, Durant’s expensive purchases had put GM in financial constraints and Billy was forced out. Under the new management structure, several brands, including Elmore were shut down in 1912. By the time Durant regained control of GM in 1916, the US two-stroke was finished.

Japanese ‘Kei’ cars

Kei cars past and present – Autoevolution

The kei category was created by the Japanese government in 1949, to stimulate car ownership and growth of Japan’s post-War car industry. Kei two-stroke engines were manufactured by Suzuki, Daihatsu, Honda, Subaru and Mitsubishi.

At first limited to a displacement of just 150cc (only 100cc for two-stroke engines), dimensions and engine size limitations were gradually expanded in 1950 (four-stroke 300cc and two-stroke 200cc), 1951 (360cc and 260cc), 1955 (360cc for four-strokes and two-strokes) and 1976 (550cc for both types).

The kei engine size limit was raised to 660cc in 1990, but by then all the two-stroke engines had been eliminated by emissions laws.

The first-generation Suzuki Sunlight (1955) featured a 360cc two-stroke engine. The 4×4 Suzuki ‘Jimny’ LJ10 also used the 360cc two-stroke engine, then 546cc in the LJ50 that sold well in Australia.

German and Italian ‘bubble’ cars

As with bombed-out Japan, Italy’s and Germany’s industries had been devastated by World War II and there was very little spending power in their economies until the 1960s. So, the German and Italian bubble cars of the post-War era were the European equivalents of the kei cars.

Most of the European ‘bubble’ cars used small, economical, two-stroke engines.

1956 Fuldamobil – R M Sotheby’s

The Fuldamobil series of lightweight microcars is credited with inspiring the term: bubble car, thanks to its shape. Fulda was best known then as a tyre maker of some 30+ years standing, but in post-War Germany it was a case of: ’do what you can’. 

Fulda turned its hand to minicar production in 1951, making a series of small vehicles that were powered by sub-200cc two-stroke engines and featured aluminium, then FRP bodies. Most were three-wheelers, but some had four.

Fulda never committed to full-scale series production, but Fuldamobils were licence-built in the UK, Netherlands, Chile and Sweden.

Weirdly as it seems, the Fuldamobile was one of the first cars to pioneer ‘negative scrub radius’ steering geometry’ that is in common usage in today’s vehicles.

Messerschmitt Kabinenroller – Stephan Kuhn

Messerschmitt’s aircraft-production days were over in 1945, so the company turned to producing microcars. The FMR/Messerschmitt KR175 used a 173cc Fichtel & Sachs, two-stroke, single-cylinder engine and the KR200 used a 191cc version. The motorcycle transmission had no reverse gear, so the engine was stopped; the key pushed in further and then restarted; after which it ran ‘backwards’, giving the little car four reverse gears!

In keeping with Messerschmitt’s aircraft heritage, seating was in-line tandem and entry was via a lift-up canopy. The steering system was also aircraft-like, with a lateral ‘stick’ rather than a wheel. 

Australian comedian and actor, Buster Fiddess, could be seen running around Sydney CBD in his Messerschmitt, in the early 1960s.

Goggomobil T250 – Lothar Spurzem

The ‘Goggomobil’ range of microcars and microvans was built by Hans Glas GmbH and the odd name  these microcars featured an air-cooled, two-stroke engine and were available in sedan, coupé, and van variants.

The Goggomobil name came from Goggo: Hans Glas’ grandson’s nickname!

The engine was a rear-mounted, two-cylinder, 250cc two-stroke and later versions had 300cc and 400cc sizes. One variant had an advanced pre-selector Getrag transmission.

The Australian Goggomobil Dart sports car derivative was built on the sedan platform, but with FRP bodywork. We’ve covered this model in our Buckle Car Brand story.

1952 Kleinschnittger F125 Roadster – R M Sotheby’s

The 1950-57 Kleinschnittger F125 German microcar featured minimalist aluminium-body design and a 125cc, ILO, 5.5bhp two-stroke engine. Around 2000 examples were sold. The later, F250 model was equipped with a 15bhp, 250cc engine, but only 22 were sold.

The F125 looked remarkably like a ‘dodgem’ car and weighed only 135kg. That light weight was handy, because the motorcycle box had no reverse gear: to back up the F125 you simply lifted the rear end off the ground and walked the vehicle into the desired forward direction!

Isetta 300 – Underwhelming Cars

The Italian Isetta, front-entry car was designed by Iso SpA and was powered by a 236cc, split-single, two-stroke motorcycle engine. 

It was subsequently built under licence in Argentina, Spain, Belgium, France, Brazil, United Kingdom and Germany, making it the most successful bubble car. However, when BMW licensed the Isetta, it re-engineered the car and swapped the two-stroke engine for its own four-stroke motorcycle engine.

Vespa 400 – BlueBreezeWiki

The Vespa 400 was a rear-engined microcar, produced by ACMA in Fourchambault, France, from 1957 until 1961, to a design by the Italian Piaggio company. Three different versions were sold:  Luxe, Tourisme and GT. 

All these model descriptions were euphemistic, considering that the little Vespa had tubular frame seats, a full-length cloth roof, fixed side windows and a13bhp or 14bhp two-cylinder, 393cc, two-stroke engine. Its only concession to two-stroke modernity was an automatic device to add oil to the fuel.

Vespa 400 engine – Jedi

The standard transmission was a three-speed, but the GT scored four! The three-speed model needed 22 seconds of foot-flat action to propel the car to 60km/h.

Astra

JARC/Astra Delivery Van – Portaroumm

The Astra, (Little Horse), was an English car built by a subsidiary of British Anzani of Hampton Hill, Middlesex, from 1954 until 1960. At Stg£348 it claimed to be the smallest and cheapest four-wheeler on the British market. It could also be bought in DIY kit form.

The Astra had originally been built by JARC and sold as the Little Horse.

The Astra was powered by an underfloor, rear-mounted 322cc, air-cooled, twin-cylinder, two-stroke engine that drove the rear wheels through a three-speed motorcycle-type gearbox. (That meant stopping the engine and running it backwards to achieve reverse gearing!)

The steel channel section chassis had all-around independent suspension, with swing axles at the rear. Most aluminium-bodied cars had two seater estate car bodies, but some four-seat saloons were also made.

After production ceased, some coupés were made by Gill cars and sold as the Getabout. The rights were also bought by Harold Lightburn of  Adelaide, Australia, who fitted a new glass-fibre estate body and sold the car as the Zeta between 1963 and 1966.

Berkeley

1958 Berkeley SE328 – R M Sotheby’s

Berkeley Cars Ltd produced economical sporting microcars with motorcycle-derived engines from 322cc to 692cc and front wheel drive between 1956 and 1960. About 4100 cars were sold.

What directors Panter and Bond wanted to achieve was: “Something good enough to win World 750cc races… but cheap, safe, easily repairable and pretty”. They did just that, for five years, with numerous motor sport successes.

The ‘Sports’ (type SA322) two-seater open tourer design capitalised on Berkeley’s GRP experience and consisted of three large mouldings, with no conventional chassis.

Power was provided by a British Anzani, twin-cylinder, 322cc two-stroke engine, mounted transversely and producing 15bhp (18bhp in the later SA328). Drive was via a chain and three-speed gearbox. The engine incorporated a rotary inlet valve mechanism in the centre of the crankshaft.

The car had all-independent suspension by coil springs and weighed only 274kg.

The SE492 had an Excelsior 500cc engine, with 30bhp and a four-seater body option.

Later Berkeleys had four-stroke engines, except for the three-wheel T60 that was introduced in late-1959, with the 328cc two-stroke twin. Three-wheel T60 two- and four-seaters were still in production when the company folded in 1961.

FSO

The FSO plant was established in 1948 by the communist Polish Government, to produce automobiles. The first FSO car was the Warszawa which was essentially a Polish manufactured re-badge of the side-valve-engine-powered GAZ-M20 Pobeda, built under licence from the Soviets.

In 1953, an in-house team started development of a smaller and cheaper car, resulting in FSO’s second model: the two-stroke Syrena. The Syrena was powered by an in-house, two-cylinder engine and was introduced in 1957.

Production continued with only minor upgrades until 1983 and 521,311 cars were produced. All were two-door sedans with two-stroke engines, initially 746cc, two-cylinder. In 1965 the Syrena received a larger, 842cc, three-cylinder engine.

The Syrena was produced in various models: 100, 101, 102, 103, 104 and the most popular, 105.

Goliath

1931 Goliath Pionie – Lothar Spurzem

Goliath-Werke Borgward & Co was founded by Carl F W Borgward and Wilhelm Tecklenborg in 1928, as part of the Borgward group. Goliath was based in Bremen and specialised in three-wheel and four-wheel cars and trucks. 

We’ve focussed on its two-stroke car products, led by the Goliath Pionier of 1931, which had three wheels and a one-cylinder engine. 

Post-War came front-wheel-drive, two-door sedans, station wagons and coupes.

Goliath GP700 – Lothar Spurzem

The GP700 (1950–1957) was powered by an in-line, two-cylinder, two-stroke, 688cc, water-cooled, transverse engine to which, in 1952, Goliath introduced Bosch direct fuel injection: one of the first cars to use this technology. It was joined by the Goliath GP900 (1955–1957) that had a larger, 886cc engine.

A bigger, 1093cc, four-stroke, boxer engine was introduced in 1957 and the two-stroke models were then given the Hansa brand name, but the Borgward Group closed down in 1961.

Gutbrod

Gutbrod was a German manufacturer of cars, motorcycles and small agricultural machinery, founded in Ludwigsburg, Germany by Wilhelm Gutbrod in 1926. 

The company originally built Standard-branded motorcycles. In 1933 the company relocated and Standard Superior cars were built, with rear-mounted engines.

1951 Gutbrod Superior Sport Roadster with Wengler body – Alexander Migl

An updated version of the Gutbrod Superior, introduced in 1953, benefited from Bosch fuel injection, as did Goliath.

The small Gutbrod Superior model was produced from 1950 until 1954, using the company’s own, front-mounted, twin-cylinder, two-stroke engines, initially of 593cc. In April 1953 the engine size was increased to 663cc in Luxus 700 versions.

Claimed power output was 20bhp for the base version, while for the larger engine, 26bhp (carburettor)) or 30bhp (fuel injection).

Only 7726 cars were produced before the factory was forced to close, but in 1956, the Norwegian Troll car was built on a Gutbrod chassis – pioneering the use of fibreglass in automobile coachwork in Europe.

If we’ve missed any two-stroke car makers, please let us know!

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