The W engine configuration was an uncommon but fascinating type of mechanical layout for internal combustion engines that was employed in some automotive and aircraft applications from the early 20th century through the 1950s. Though certainly unconventional compared to the more traditional straight, V, or radial configurations, W engines offered some potential benefits that attracted engineers seeking novel solutions or performance improvements. This research paper will explore the history and design of W engines, technical challenges involved, notable applications, and reasons for their eventual discontinuation despite early promise.
One of the earliest patented W engine designs was created in 1909 by American engineer James S. Owen, who sought an engine architecture with balanced primary forces to minimize vibration. The Owen W engine stacked two cylinder banks at a 45-degree offset from each other, with each bank canted inward toward the other. This layout positioned the opposing pistons so their sideways forces counteracted each other, contributing to impressive smoothness even at high rpm. Owen’s concept recognized the potential of the W configuration for balancing while also increasing power output by effectively combining two smaller engine blocks into a compact package with fewer parts than a larger straight or V engine of equivalent displacement.
In the 1920s, several European automakers began experimental work with W engines to squeeze more power from smaller engine compartments in sports cars. Due to their inherently narrow profile, W engines took up less longitudinal space than a straight or V engine of comparable displacement. At the time, increasing horsepower in small, nimble sports cars while staying within tight layout constraints was seen as an advantage. One of the more unique early W engine powered vehicles was the 1922 Excelsior W-8, an Italian motorcycle with a tiny 8-cylinder W config engine producing an then-astounding 50 horsepower from just 1.1 liters of displacement.
W engines also posed new technical challenges compared to more conventional engine architectures. Balancing the primary and secondary forces of two banks meeting at an angle required precision in design and manufacturing. Oil and coolant flow paths were complicated, and accessories like carburetors or fuel injectors had to be creatively packaged in the tight center space between cylinder heads. Further, access for maintenance and repairs was hindered by the crowded design. These downsides meant W engines were more difficult and expensive to design and produce in smaller volumes compared to straight or V engines.
Nonetheless, W engine development continued through the 1930s, sometimes driven more by quests for novelty rather than pragmatic motives. Examples include the unique Mercedes-Benz W25 test car from 1934, powered by a 3.5L supercharged W12. Even more exotic was the Huckaby W16 aircraft engine built in the U.S. in 1937, packing 16 cylinders into a remarkably short powerplant just over 3 feet long. These remained one-off prototypes not put into production.
One of the most prominent production W engines was used in Germany’s BMW 132 luxury sedan from 1938-1941. BMW’s innovative 3.2L aluminum alloy W12 engine offered smooth power and high performance potential from a surprisingly small package, fitting amidships in the 132’s sleek body. With all-aluminum construction and twin overhead cams, the BMW W12 produced an impressive 130hp from just 3.2 liters while maintaining a low cruising rpm.
By World War 2 the technical difficulties of series production for W engines started to outweigh potential benefits for automakers. The majority of W engine development efforts through the late 1930s failed to demonstrate compelling advantages over more mass-producible straight or V engines that could also now offer comparable power-to-size ratios thanks to advances like overhead valves and multi-carb induction.
Following the war, only limited efforts persisted with W engines in heavier-duty off-road and marine applications where size/weight constraints remained an important factor. In 1947-48, GM produced the GMC TDH-5105 6×6 truck with a unique W18 diesel design exhibiting an unusual “split” layout with two banks at 90-degrees to each other. The large displacement W18 turned slowly for abundant torque hauling loads over tough terrain. Sintesi also built W16 and W18 diesel engines in Italy through the 1950s for marine and industrial use cases favoring compact dimensions.
Outside of specialized heavy-duty roles, the complexity and cost challenges of W engines could not be justified against more highly refined mass-production straight and V engine layouts taking hold across major automakers. By the late 1950s, W engines had nearly vanished from all automotive and aviation applications in favor of straighter-forward mass manufacturing techniques. Many technology advancements like fuel injection and multi-valve cylinder heads evolved straight and V designs enough to match or surpass the power densities and smoothness that were once potential benefits of a W configuration.
While never reaching high-volume production like conventional engine architectures, W engines demonstrated from their early 20th century inception the potential advantages of a compact, narrow-profile design achieving primary/secondary balance through internal cylinder bank opposition. Notable applications included exotic interwar sports cars and BMW’s lauded W12 powered 132 luxury sedan. Complex manufacturing, increased costs, and difficulty servicing ultimately caused W engine development efforts through the 1950s to fade out as offsetting technical benefits diminished against evolving high-performance straight and V engine technologies better suited for mass production. Although unconventional, W engines remain an intriguing historical example of engineers striving for new solutions within the constraints of automotive design.
Andrew Stroud