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 30ð. Displacement ranged between , and all production XU gasoline engines had a bore of . The engine uses an aluminium cylinder head in all models. All models' blocks are made, except XU10, in cast aluminium alloy with removable cast iron wet cylinder liners. XU10 blocks are made in cast iron, with bores machined directly in the block, without removable cylinder liners. Its first Citroën application was on the Citroën BX in 1982, where it appeared in format.
The XU was replaced by the more modern EW/DW family.
The XU5 had a displacement of , with a bore and a stroke of . All XU5 engines were SOHC 2-valve per cylinder designs. They used either a single or double-barrel carburetor, or fuel injection, depending on model. Output ranges from .
The XU7 had a displacement of , with a bore and a stroke of . All XU7 engines used fuel injection, with a 16-valve DOHC version, the XU7 JP4, also produced. Output ranged from .
The XU8 had a displacement of , with a bore and a stroke of . The only engine in this family is the 16-valve DOHC turbocharged XU8 T which was fitted to the Peugeot 205 Turbo 16.
The XU9 was the predecessor to the XU10 and had an aluminum block with wet iron liners. It had a displacement of , with a bore and a stroke of . Many versions were produced, from a double-barrel carburetted 8-valve to a 16-valve DOHC fuel injected model. Output ranged from .
The XU10 has a cast iron block with a displacement of , with a bore and stroke of , making it a square engine. Many versions were produced, from a double-barrel carburetted 8-valve to a 16-valve DOHC, fuel injected, turbocharged model. Output ranged from .
The XU engine was used in motorsport for over 3 decades.