Most cars these days have boring engines. I4, Flat-6, V8, V12. Always with the even numbers, the modern car is. But I feel like some odd numbers today. Three-cylindered wonders, five-pistoned marvels, even those with nine cylinders.
Some of the prettiest engines with odd numbers of cylinders were radial engines, especially the ones from World War II. The one pictured above is a nine-cylindered Wright R-1820 that eventually was one of four that powered a B-17 Flying Fortress. The Wright R-1820 produced anywhere from less than 700 horsepower to more than 1,500 horsepower, depending on the application.
The only problem with radial engines is they tend to be, well, absolutely ridiculously enormous. That's not really a problem if it's stuck on a big plane, but it's a slight issue when you're trying to fit one into a car. There have been a few cars fitted with radials before, but they tend to look ridiculous.
But surely there are better examples out there, between Smart Cars and Volvos and the like. Show us the best odd-cylindered engines in the comments below!
Photo credit: Library of Congress