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°. Displacement ranged between 1580 and 1998 cc, and all XU gasoline engines had a bore of 83 mm (3.3 in) or 86 mm (3.4 in). Its first Citroën application was on the Citroën BX in 1983, where it appeared in 1580cc format.
The XU was replaced by the more modern EW/DW family.