Citroën M series petrol engine 

The Citroën M-series engine is an internal combustion automotive petrol engine developed and produced by Citroën from 1974 to 1991.

History

The M-series engine available in gasoline and four-stroke diesel with four in-line cylinders, cast iron block, water-cooled, fitted with a five-bearing crankshaft, with controlled lateral camshaft. by timing chain or cascade of pinions (for atmospheric diesel up to January 1984). It is capped by an aluminium cylinder head with eight valves controlled by manually adjustable rocker arms. 

The M series engine was fitted to the Citroën CX ,it  is an evolution of the original D series engine, used by Citroën DS and ID. They have notable differences. First of all, the block is designed for transverse installation, unlike the DS and ID where it was longitudinal, and the lower engine is revised accordingly in order to transmit traction to the front wheels. The direction of rotation of the motor is clockwise (distribution side), while the D series motor Turns counter clockwise. In addition, in order to house this block in the body of the CX, it is tilted 30 degrees forward to reduce the height under the hood. The first version marketed was the 2-liter petrol directly derived from the DS20 engine. The 2.2 and then 2.3 liters are subsequently added, derived from the DS21 and DS23 models. A 2.5-liter petrol will also make its appearance to replace the 2.3l. The 2.5 petrol will even be equipped with a turbo thereafter, first without an air-to-air exchanger (intercooler) then with an exchanger currently in production of the 2nd series .

Petrol engines

• 2 liters: Type M20 / 616, bore 86 mm, stroke 85.5 mm, for a total displacement of 1 985 cc. Powered by Weber double barrel carburetor, compression ratio increased to 9: 1. Maximum power 102 DIN hp at 6000 rpm, maximum torque 152 Nm.
• 2.2 liters: Type M22 / 617, retains the dimensions of the 2.2 D series engine with 90 mm bore and 85.5 mm stroke for a displacement of 2175 cc. Powered by Weber double-barrel carburetor, compression ratio 9: 1, power 112 hp DIN at 5500 rpm, maximum torque 167 Nm at 3500 rpm.
• 2.3-liter: Type M23, introduced in 1976, retains the dimensions of the 2.3 D-series engine with 93.5 mm bore and 85.5 mm stroke for a displacement of 2,347 cc. This engine was the only one of the “M series” to be powered either by a carburettor or by electronic injection:
• Carburettor version (Weber double-barrel): compression ratio 8.75: 1, maximum power 115 DIN hp at 5500 rpm, maximum torque 180 Nm at 2750 rpm. From 1980, this engine underwent a slight modification in order to improve performance: maximum power increased to 120 hp at 5500 rpm and torque reached 196 Nm at 2750 rpm.
• Bosch L-Jetronic multi-point injection version, type M23 / 622, introduced in 1977: compression ratio 9: 1, maximum power 128 hp DIN at 4800 rpm, maximum torque 197 Nm at 3600 rpm. Slight improvements from 1980: maximum power 130 hp, maximum torque 201 Nm.
• 2.5 liters: introduced in 1983, replaces 2347cm3. Compression ratio 8.75: 1, bore 93 mm, stroke 92 mm, displacement 2,500 cc. Fuel supply only by Bosch LE-Jetronic multi-point electronic injection. Maximum power 138 DIN hp at 5000 rpm, maximum torque 211 Nm at 4000 rpm. In the catalysed version, power and torque drop to 123 hp and 191 Nm respectively.
• 2.5 liters Turbo: Introduced in 1984, supercharged version of the 2500 cc, initially without air-air exchanger. The compression ratio goes down to 7.75: 1 to tolerate turbocharging by Garrett TO3 turbo with maximum pressure of 0.7 bar. Fuelled by Bosch LE-Jetronic multi-point injection, maximum power 168 DIN hp at 5000 rpm, maximum torque 294 Nm at 3250 rpm. These characteristics remain unchanged on paper with the arrival of the air / air exchanger and a compression ratio dropping to 8.5 / 1 in July 1986 (model year 87) which however allows a clear reduction in consumption at high speed and in the oil temperature under sustained use. On the catalysed version, power and torque drop to 160 hp and 275 Nm respectively.