The PSA XUD is a diesel engine designed and built by PSA - Peugeot and Citroën. It is an Indirect injection (IDI) engine, that uses a version of the Ricardo Consulting Engineers Ricardo Comet V prechamber cylinder head design.^[1] The engine comes in 1.8 L (1,769 cc), 1.9 L (1,905 cc), and 2.1-liter displacements. The 2.1 has 12 valves, all displacements were built either naturally aspirated or turbocharged. The XUD was the predecessor to the HDI range of engines. Early HDi Engines were a PSA design, later 16-valve engines were jointly developed with Ford.

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PSA XUD engine
XUD9 in a Citroën BX TRD
Overview
Manufacturer	PSA
Production	1982–2001
Layout
Configuration	Inline-4
Displacement	1.8 L (1,769 cc) 1.9 L (1,905 cc) 2.1 L (2,088 cc) 2.1 L (2,138 cc)
Cylinder bore	80 mm (3.15 in) 83 mm (3.27 in) 85 mm (3.35 in) 86 mm (3.39 in)
Piston stroke	88 mm (3.46 in) 92 mm (3.62 in)
Valvetrain	SOHC 2 valves x cyl. or 3 valves x cyl.
Combustion
Turbocharger	With intercooler (some versions)
Fuel system	Indirect injection
Management	Lucas, Bosch
Fuel type	Diesel
Cooling system	Water-cooled
Output
Power output	60–110 PS (44–81 kW; 59–108 hp)
Dimensions
Dry weight	157 kg (346 lb)
Emissions
Emissions control systems	Catalytic converter

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The XUD was available with either SOHC 8-valve or 12-valve heads. It was mainly applied transversally in front wheel drive vehicles, tilted by 30°. However, some applications in non-PSA vehicles had the engine installed longitudinally, with rear-wheel drive. The XUD is built in Citroën's plant in Trémery, near Metz.^[1]

Displacement ranges between 1.8 and 2.1 L (1,769 and 2,138 cc), and all XU diesel engines have a stroke of either 88 or 92 mm (3.46 or 3.62 in). The former was shared with the XU9. Bore sizes range from 80 to 86 mm (3.15 to 3.39 in), some of which are also shared with other XU engines.

Upon its release the engine was noted as one of the best diesel engines (for cars and light vans) in the world with its high power output and refinement it made all other diesel engines seem agricultural.^[1] It was also particularly light, with a ready-to-run XUD9 weighing 157 kg (346 lb), 15% less than a comparable diesel of the previous generation.^[1]

The XUD7 has a displacement of 1.8 L (1,769 cc), with a bore and a stroke of 80 mm × 88 mm (3.15 in × 3.46 in). Output is 60 PS (44 kW; 59 hp) for the naturally aspirated version or 78 PS (57 kW; 77 hp) for the turbocharged model. An intercooled turbocharged version was introduced later, with 90 PS (66 kW; 89 hp) on tap. All are Diesel engines.

The XUD9 has a displacement of 1.9 L (1,905 cc), with a bore and a stroke of 83 mm × 88 mm (3.27 in × 3.46 in). Both turbocharged and naturally aspirated versions were produced. Most turbocharged versions feature an intercooler, although a limited number of installations in the Citroën Xantia featured a Turbocharger without intercooler. Both engines also featured either a Bosch or a Lucas mechanical fuel pump and injectors. The engine version with the Bosch pump is known to have been run with vegetable oil. The original XUD9 engine is known as the "square port" engine, as its cylinder head has square exhaust ports. Later (and noticeably improved) XUD9A engines have oval ports.

PSA Group licensed a modified version of the naturally aspirated version of the engine with a catalytic converter designated the XUD9/Z to Hyundai which was rated at 50kw. It was used in the European specification of the Lantra (1996–1999).

The XUD11 was available in two displacements:

• 2.1 L (2,138 cc) — XUD11 A naturally aspirated
• 2.1 L (2,088 cc) — XUD11 ATE/BTE turbocharged

Both were 12-valve SOHC engines with a 92 mm (3.62 in) stroke. The naturally aspirated XUD11 A was bored to 86 mm (3.39 in) for a total displacement of 2.1 L (2,138 cc), while the turbocharged ATE/BTE versions were reduced in bore to 85 mm (3.35 in) for a total of 2.1 L (2,088 cc). The BTE engines used a Lucas EPIC (Electronically Programmed Injection Control) fuel pump, whereas the ATE engines used a Bosch injection pump with a throttle cable.^[6]

The engine has been installed into the following vehicles:-