Why do motorcar engines stop at V12? why isn’t there a V 16 or V20?
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A V12 is physically a very big engine. Packaging it in a modern car is difficult. A V16, with 33% more cylinders, would be even bigger, heavier and more cumbersome. This is why it has rarely been tried in cars, and even when it was it was in specific niche categories like racing and luxury cars. Cadillac and Marmon built V16 luxury road cars in the 1930s, while Cizeta built a V16 supercar in the 80s. Auto Union and BRM built V16 F1 cars, AU before WWII and BRM in the 1950s.
Other companies have built other types of 16 cylinder car engines, mainly for racing. Porsche built a flat-16 version of their mighty 917 sports racing car, but decided to build a turbo version of their flat-12 car instead as they felt it had more potential. The resulting 917/30 turbo flat-12 Can-Am car was known as the ‘Turbopanzer’ and was for a long time the most powerful circuit racing car ever built. Bugatti also built a car with a U16 layout, which was effectively two separate inline 8 cylinder engines geared together.
In the 1960s, not content to rest on their laurels with the insane 1.5l supercharged V16 they built in the 50s, BRM entered the 3.0l F1 era with a monstrosity called an H16, which was effectively two 1.5l flat-8 engines mounted one on top of the other. It was, unsurprisingly, big, heavy, complex, unreliable and caused mounting problems as it had to sit very high to let the exhausts of the lower bank of cylinders pass underneath it. It somehow won one race before it was replaced with a V12.
I have never heard of a V18 or V20 being designed for car use, as by the time you get to that many cylinders the engine’s crankshaft potentially starts becoming very long and flexible, meaning the engine can develop issues with vibration, fatigue and even harmonics, causing it to rip itself apart from the inside. I am willing to be proved wrong, though, if anyone knows of such an engine.
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