Mercedes-Benz M112 engine

Mercedes-Benz M112 V6 engine

The Mercedes-Benz M112 was a six-cylinder V6 petrol engine that was introduced in 1997 to replace the M104 engine. The M112 engine was manufactured in Bad Cannstatt, Germany, though the supercharged 3.2-litre AMG version was assembled in Affalterbach, Germany.

Closely related to the M113 V8 petrol engine, the M112 engine had cylinder spacing of 106 mm, a 90-degree ‘V’ cylinder configuration, sequential fuel injection, an alloy cylinder block with cast-in Silitec (Al-Si-alloy) cylinder liners, forged steel connecting rods, iron-coated aluminium pistons, an alloy cylinder head, a single overhead camshaft (SOHC) per cylinder bank (driven by a double-roller chain), two spark plugs per cylinder and a magnesium dual-length intake manifold.

The M112 engine had two intake valves and one exhaust valve per cylinder that were actuated by roller rockers. The use of one exhaust valve per cylinder was chosen to minimise heat losses when cold and enable the catalytic converter to reach its operating temperature faster. On the crankshaft in the cylinder V, a seated balancer shaft rotated opposite to the crankshaft at the same speed to counteract first-order mass rocking motions.

Although the M112 engine was superseded by the M272 engine in 2004, it continued to be used in the Mercedes-Benz W639 Viano.

Mercedes-AMG supercharged M112 V6 engine

Developed for the W203 C 32 AMG and R170 SLK 32 AMG, the supercharged M112.960 and M112.961 engines were assembled by hand at the Mercedes-AMG plant in Affalterbach. These engines were fitted with a twin-screw, belt-driven IHI supercharger which, to minimise fuel consumption, was activated by an electromagnetic coupling according to load and engine speed conditions. The supercharger featured Teflon-coated rotors – which could achieve 20,700 rpm at maximum engine speed – and provided peak boost pressure of 1.22 bar (17.7 psi). The water/charge-air cooler was mounted between the cylinder banks and connected to a separate radiator that was located at the front of the vehicle in the fresh air stream. While peak torque was 450 Nm at 4400 rpm, over 400 Nm was available from 2300 rpm.

Compared to the standard M112 engine, changes for the supercharged M112.961 engine included:

• A new crankshaft with bearings adapted to the high torque;
• New connecting rods;
• A temperature-resistant coating for the pistons to withstand peak pressures in excess of 90 bar;
• A new balancer shaft;
• A higher-volume oil pump for increase oil supply to the oil nozzles (which had a 70 pr cent higher output);
• Lightweight, assembled camshafts;
• Harder valve springs to increase the rated engine speed (from 6000 rpm to 6220 rpm) and resulting valve forces;
• An air pressure sensor instead of the usual hot film air mass meter; and,
• A unique exhaust system with four ceramic catalytic converters.

A derivative of the M112.960 and M112.961 engines was developed for the Chrysler Crossfire Coupe SRT-6 and Chrysler Crossfire Roadster SRT-6. For the Chrysler Crossfire SRT-6 models, however, peak boost pressure was 1.0 bar such that its peak outputs were 246 kW at 6100 rpm and 420 Nm at 3500-4800 rpm, rather than the 260 kW at 6100 rpm and 450 Nm at 4400 rpm of theC 32 AMG andSLK 32 AMG.