A U engine is a piston engine made up of two separate straight engine engines (complete with separate crankshafts) joined by gears.
This configuration is uncommon as it is heavier than a V design, it main interest is to share common parts with Straight engines.
An engine of this type was the 16-cylinder engine found on the Bugatti Type 45, and only two were produced. However, Bugatti licensed the design to Duesenberg in America, who produced about 40, and Breguet of France, who both intended the engine for aircraft use.
Matra develloped a high-end Bagheera prototype powered by a 2,6 L U8 engine made of two Simca 1000 Rallye 2 Straight-4 connected by chains around 1974. However with petroleum crisis this car was never put in production.
