The PSA XU is a family of internal combustion engines used in Citroën and Peugeot automobiles. It became the dominant mid-size engine in Peugeot and Citroën products through the 1980s and 1990s.The XU design was introduced in 1981 with the Peugeot 305. It was a SOHC or DOHC straight-4 design with two or four valves per cylinder, using petrol as fuel. It was applied transversely in front wheel drive vehicles only, tilted by 30°.