The Big DKW 4=8

DKW made its name with its range of small, two-stroke engined, front-wheel drive cars. Introduced in 1930, the F (Frontreib) series went through a rapid evolution to become the second best-selling car in Germany by 1935. However, DKW also produced a range of mid-sized cars targeting the more affluent middle class in a separate factory in Spandau, near Berlin. Imaginatively named the "Big DKWs”, this range was fraught with mechanical problems and did not enjoy the market success of the DKW Front range, but despite this DKW persisted with the range right up to 1940.

Inherent problems of the two-stroke engine
DKW founder, Jorge Rasmussen, was convinced by the efficiency and simplicity of the two-stroke engine, but although they had good power to weight ratio for their size, all two-stroke engines suffered problems with thermal efficiency and the loss of unburnt fuel. Many solutions were attempted, including deflector pistons, port positioning and gas-flow scavenging, but none of these were entirely resolved the issue.

In 1927 DKW introduced a new 500cc twin-cylinder air cooled engine, called the Type Z. This engine used deflector pistons to improve gas flow in the combustion chamber, but uneven combustion led to overheating at the rear of the cylinders when in prolonged use. To address the overheating issue, DKW engineers installed a water jacket around the engine, changing it from air-cooled to water-cooled.

Cooling was effected via a small radiator mounted ahead of the engine. The Z 500 wasn't a particularly successful motorcycle however and the company quickly retired the model. This was to be the only water cooled motorcycle DKW would ever build.

DKW's first car - the DKW P-15

In the mid-1920s DKW had experimentally fitted two-stroke stationary motors to Slaby-Beringer elektrowagens, but these proved not particularly successful. The small capacity air-cooled engines used were not efficient enough to reliably power a small car. The new water-cooled Z-engine however appeared more promising, so the engineering team at DKW's Spandauwerkes initiated a new car project. Using the DEW electrowagen as a basis (https://dkwautounionproject.blogspot.com/2019/10/1926-dew-electrowagen.html), they developed a small plywood bodied car powered by a Z-engine bored out to 600cc capacity, delivering 15 brake horsepower. The engine was mounted inline and power was delivered to the rear wheels via a traditional prop shaft and differential. The car itself was constructed as a self-supporting plywood box and did not have a chassis. The P-15 went on sale in 1928 and over 3,000 cars sold. https://dkwautounionproject.blogspot.com/2017/07/1929-dkw-p-15-brochre.html

The P-15's 600cc engine proved to not to be entirely satisfactory so DKW engineers continued to investigate other solutions. One option was to use a charging pump to fill and clear the cylinders. This was method that would later be used with great success by DKW's motorcycle racing division.

Schematic of the V4 engine. The charging pistons are at the front of the engine, on the right. The pistons were driven by the crankshaft like the power cylinders, but without ignition.

The new charging pump engine comprised two three-cylinder engine blocks in a V-arrangement, driving a central crankshaft. The first two cylinders were used as charging pumps, receiving and compressing the fuel mixture before pumping it into the four combustion chambers. This complex piece of engineering had a notional capacity of 1000cc and delivered an estimated 25 brake horsepower. One of the (many) drawbacks of the design however, was that the crankcase was not lubricated by the petroil mix, requiring an oil sump and splash lubrication system like that in a four-stroke engine.

Like the P-15, the new car was also constructed as a chassis-less, self-supporting plywood box. The engine was mounted inline, driving the rear wheels via a differential. The gear shift was floor mounted, directly to the back of the gearbox. The car came as a two-seater two-door cabriolet, four-seater two- door cabriolet, and four-seater limousine versions. The car was designated the '4=8 Big DKW.'

The 4=8 hit the market in 1929 – just in time for the Wall Street Crash. The resulting economic downturn helped suppress sales of the Big DKW, which were lukewarm at best. Sales were hampered by the car's complex engine. Firstly, owners who failed to monitor oil levels in the sump – unnecessary in other two-stroke engines – quickly burned out their cranks. Secondly, the distributor ignition system, which was adapted from a four-stroke engine, was forced to work doubly hard in a two-stroke motor, rapidly burnt out the distributor and spark plugs. Fuel consumption was also high and the engine was noisy and vibrated excessively. Damage to the plywood structural members due to vibration was commonplace and, as the car had no chassis, was problematic to repair.

Rasmussen looks to break into a new market – in vain
In the meantime, DKW’s energetic director, Jorge Rasmussen, had been busily expanding his business empire. In 1927 he had traveled to the US where be purchased the bankrupt Rickenbacker motor car company. His sole intent behind the purchase was to sell the company’s 6 and 8 cylinder four-stroke engines to other German manufacturers. A large portion of DKW's income was derived from sales or generic two-stroke industrial and motorcycle engines to other manufacturers. Rickenbacker’s plant and designs were dismantled and shipped to Germany.

World War I flying ace Eddie Rickenbacker with his 1924 Rickenbacker coupe. Rickenbacker lent his name and face to the company but otherwise was not involved with the business.

On his return, he was presented with another opportunity, this time in the form of the insolvent Audi motor company. Rasmussen’s financiers, the Bank of Saxony, were desperate to offload the company before it went bankrupt and encouraged Rasmussen to buy the ailing company in 1928. Audi's financial position was dire but Rasmussen saw an opportunity to break into the luxury car market. https://dkwautounionproject.blogspot.com/2018/02/1928-audi-eight-cylinder.html

1927 Audi 14 50ps. Before Rasmussen bought the company Audi's sales were pitifully low - around 20 cars per year.

However, if Rasmussen believed that Audi and Rickenbacker would advance his automotive ambitions, he was to be sadly mistaken. Despite all the cost and effort involved in setting up the Rickenbacker plant in Germany, when the engines finally began rolling of the production line they failed to attract any buyers. Production was stopped by 1930. https://dkwautounionproject.blogspot.com/2020/07/1930-rasmussen-6-and-8-engines.html

Audi proved to be in a much worse state than Rasmussen was led to believe and he was forced to ruthlessly purge the company of its expensive and unsaleable model range. He shut down Audi’s engine plant and installed his surplus Rickenbacker engines in the next two new Audi models, the SS and the Dresden. Neither car found a market and less than 100 of both types were built between 1931 and 1932.

Rasmussen's last throw of the Audi dice - the Audi P

In a last ditch effort to save Audi, Rasmussen decided to re-engine the DKW 4=8 with a 1.2 litre Peugeot four-cylinder engine and badge it as the Audi P. Although aimed at the middle class market, even this car failed to sell as customers preferred to buy the troublesome two-stroke powered DKW 4=8 car over the Audi car by a margin of 10 to 1. https://dkwautounionproject.blogspot.com/2021/01/1931-audi-type-p-last-throw-of-dice.html

The Audi P and DKW 4=8 side by side highlights the similarity between the models.

The radical gamble

After the failure of the Audi and Rickenbaker adventures, Rasmussen needed a surefire winner to get his company back into the black. In October 1930 Rasmussen charged the design team at the Audi plant to develop a new budget car that would undercut everything else in the market in time for the Berlin Motor Show in February 1931. The resulting car was a masterpiece of efficiency. By using front-wheel drive, the car dispensed with a heavy differential and prop shaft. The little two-cylinder two-stroke engine and motorcycle gearbox was mounted transversely across the frame. To top it off, a smart roadster body was mounted on a simple ladder chassis. Apart from the radical decision to employ front-wheel drive – the first in a production car – the car’s most important feature was its newly designed two-stroke engine.

In 1929 Rasmussen had come across an engineering patent by Dr Ing. Adolf Schnurle for a reverse scavenging two-stroke engine cycle. Schnurle had proposed the reverse scavenging concept as a technical exercise to improve heat exchange and efficiency in two-stroke diesel engines. He had published his paper, lodged a patent, and left it at that. After reading the paper, Rasmussen instantly recognized that the Schnurle patent could significantly improve two-stroke engine performance and, as the Schnurle patent used flat topped pistons, substantially reduce manufacturing costs. Rasmussen set his consultant engineer, Dr Ing Herbert Venediger, to investigate. After technical evaluation and testing, Venediger confirmed Rasmussen's assumptions, so Rasmussen rushed to meet with Schnurle and secured an exclusive licensing arrangement for DKW.

As anticipated, DKW’s new Schnurle-patent engines delivered a significant uplift in performance, endurance and fuel economy and instantly made every other two-stroke engine obsolete.
https://dkwautounionproject.blogspot.com/2020/04/portrait-of-engineer-herbert-joseph.html

The DKW F1 (Frontreib) was an instant success and the P-15, PS600 roadster and 4=8 were all retired. The Audi plant at Zwickau was given over to production of the new car.

The Poor Cousin

DKW’s Spandau plant was primarily a coachwork plant. It was here that the wooden bodies of the F1 and its successors were built before they were shipped to Chemnitz and fitted to their chassis. However, one small corner of the factory remained dedicated to the continuing development of the Big DKW. It was clear to everyone that the 4=8 engine had been rushed into production before the bugs had been ironed out. The Spandau team attempted to reduce the vibration problem by reducing the engine capacity to 800cc. Fuel and spark plug consumption were not improved however, so after trials reverted to 990cc capacity. 

In 1932 an improved version of the 4=8 was released as the Sonderklasse 1001. The wheelbase had been lengthened to 2800cms and the bodywork given more modern styling. The longer wheelbase stretched the chassis-less structure to its outer limits and when placed under great stress, the car exhibited a disturbing tendency to break in two. Nevertheless, the car continued to find a market, albeit in much lower numbers than its Front stablemate. The Sonderklasse was still a more economical car than a contemporary Wanderer, however, engine warranty repairs for the Sonderklasse became an industry unto themselves.

This contemporary cigarette card shows the self supporting wooden body and chassis.

The 4=8 engine

The Floating Car

The mid-1930s saw the beginning of the streamlining movement and in 1935 DKW unveiled its contribution – the Schwebeklasse, the replacement for the Sonderklasse. Although the drive-train was unchanged, the body was completely new. The Schwebeklasse also introduced the DKW patented 'floating axles' on the rear, which DKW exploited via highly publicized cross country trials. Here again though, the car could not escape its fundamental underlying weakness. The chassis-less body fractured under stress and the engine continued to perform poorly. A later version with a bored out 1054cc engine failed to improve its performance.

A cigarette card of the Schwebeklasse

The last throw
In the years after the National Socialists took power in 1933, Germany’s domestic economy substantially improved. In 1934 Adolf Hitler personally promoted the idea of a ‘people’s car’ and was very specific in his expectations. The German people’s car would be a modern, steel car, not a wooden or baby car. This pretty much excluded DKW’s entire range from consideration so the Auto-Union design bureau went into overdrive to develop the next generation of vehicles. For the Front range, DKW began working on an entirely new steel bodied car powered by a three cylinder two-stroke engine. This would be unveiled in 1940 as the DKW F9; the car that would restore DKW’s fortunes in post-war Germany. https://dkwautounionproject.blogspot.com/2017/07/1939-dkw-f9-prototype.html

While the DKW F9 project was underway, Auto-Union's design bureau saw opportunity to hit the market early. Wanderer already had a small middle-class car in the market in their W24 model. Re-engining this car with a two-stroke engine would go some way to reducing its cost, although nowhere near the Volkswagen's proposed 1000RM price tag. As the new 3=6 engine was not yet ready for production, the 4=8 engine was used instead. In 1937 the new car went on sale as the New Sonderklasse. The car received good reviews in the automotive press and sales were reasonable, but could not compete with budget DKW F7 in terms of sales. The engine remained the car's weak point however. Despite technical improvements, the engine still suffered from catastrophic crankshaft failure if not carefully maintained. Customers were offered two free engine replacements under warranty. After the third engine failure they were given a replacement Wanderer engine. https://dkwautounionproject.blogspot.com/2020/07/1937-dkw-sonderklasse-review.html

The 1937 Sonderklasse was basically a Wanderer W24 coupe with a two-stroke engine and different radiator grill. At 3100RM the Sonderklasse was 750RM cheaper than the basic Wanderer.

Sales continued to tick over until Auto-Union passenger car production was shut down in 1940 and the factories given over to war production. Due to their mechanical unreliability, few 4=8 cars remain today. Obviously the chassis-less wooden bodied cars were lost to rot and fire, while most of the steel-bodied Sonderklasse were lost in the war.

Why did DKW persist with what was obviously a flawed design for so long? I suspect DKW wanted to retain a larger model in the market, but had no alternative power-plant to work with. They had earlier tried to increase the capacity of the two cylinder 700cc engine to 1100cc, but encountered limitations with its performance. The 3=6 was first designed in 1936 but took several years of development to perfect. The 4=8, although a poorly performing engine, was at least available. Surprisingly, customers seem not to have been put off by the car’s engine problems and they always found a market, albeit much smaller than the market for the smaller Front model. In the course of its 10 year production run, approximately 40,000 4=8 cars of all models were produced.

1931 DKW 1001 Sonderklasse brochure: https://dkwautounionproject.blogspot.com/2017/07/1931-dkw-48-brochure.html
1932 DKW 1001 Sonderklasse brochure: https://dkwautounionproject.blogspot.com/2017/06/1932-dkw-sonderklasse-48.html
1937 DKW New Sonderklasse brochure: https://dkwautounionproject.blogspot.com/2020/06/1937-dkw-sonderklasse.html
1937 DKW New Sonderklasse review: https://dkwautounionproject.blogspot.com/2020/07/1937-dkw-sonderklasse-review.html
1937 Wanderer W24 brochure brochure: https://dkwautounionproject.blogspot.com/2020/06/1937-wanderer-w24.html