Few motorcycle companies have done more to promote the popularity of the V-twin engine than Harley-Davidson. And while we commend their efforts, it's important to remember that other motorcycles ...

First produced in 1949, the Citroën featured a 375cc air-cooled horizontally-opposed twin with 9 horsepower. The engine continued to improve over the next 42 years. The 2CV engine was built to be ...