Mercedes Muscle

One of the most common attributes of factory-backed supercharger power upgrades is that the lift in output is almost always fairly mild. Holden's supercharged engine increases power 13 per cent from 152 to 171kW, Jaguar's blown 4-litre V8 has 28 per cent more power than its naturally aspirated brother. The Mercedes-Benz SLK 230? It develops only 63 kW/litre from its blown four cylinder.

But enter the Mercedes SLK 32 and the C 32 AMG!

Sharing an engine based on the 3.2-litre V6 that in NA form already develops 160kW and 310Nm, the supercharged version lifts peak torque by 45 per cent and power by a staggering 63 per cent! Yep, this engine pumps out 260kW at 6100 rpm and 450Nm at 4400 rpm. Put that much power and torque into the mid-sized C-class body and you're talking 0-100 in this automatic trans car in 5.2 seconds!

The lighter SLK 32? AMG suggests a flat 5 seconds...

So what have the Mercedes-AMG engineers done to the engine to so radically increase its power? As you might expect, it's no ordinary bolt-on conversion.

Mechanicals

The 90-degree V6 was heavily revised for its new high-boost forced aspiration role. Interestingly, most internal alterations were aimed at improving durability, rather than breathing. Mechanical changes included:

• a new crankshaft with bearings adapted to the higher output torque
• new connecting rods
• pistons of a "highly temperature-resistant material"
• a new balance shaft
• lightweight "assembled" camshafts
• harder valve springs
• a new oil pump with a higher output, supplying to oil nozzles that in turn are upgraded in flow by 70 percent

In addition, the exhaust was re-designed to incorporate four low back-pressure thin-wall catalytic converters, and the airflow meter normally fitted to the 3.2 litre six was discarded and replaced with manifold pressure sensing.

But if the engine is the heart of the new AMG models, the supercharger is its pacemaker...

Supercharger

Unlike the Roots-type Eaton blower used on the supercharged Mercedes four cylinder engines, the 260kW engine uses a very sophisticated Lysholm-type supercharger produced by IHI in Japan. Driven at 3.3 times crankshaft speed, the helical lobe supercharger develops up to 1 Bar (14.5 psi) of boost. One of its two cast aluminium rotors is Teflon-coated (it's the yellow one), and the supercharger drive is through an air-conditioning style electromagnetic clutch. Despite the high efficiency of this design of supercharger, the blower still requires 45kW to power it when the engine is at its 6220 max rpm. Of course, the blower is also then flowing a lot of air - up to 1200kg per hour of it, in fact.

In order that the supercharger could be fitted into the already tight confines of the SLK and C-class bodies, it has been mounted within the 'V' of the V6. Sandwiched between the supercharger and the inlet manifold is a reverse-flow heat exchanger for a water/air intercooling system. Aimed specifically at reducing temperature peaks (an area where Mercedes-AMG engineers believe that an air/air system can be less effective), the system has its own radiator and electric water pump. The complete supercharger and intercooler system adds only 25kg of mass - so the power/weight ratios of the two cars equipped with the upgraded drivetrain are radically improved!

The supercharger engages only as required; when it is not being driven, the intake air flows through its rotors (ie no external bypass is fitted). Supercharger operation is dictated by the Bosch ME 2.8.1 engine management system on the basis of engine speed and load. However, the supercharger, which is driven from the engine's serpentine belt, will not engage at engine speeds over 3000 rpm - if this occurred, the belt stresses would be too high. If required, the engine can develop 400Nm from 2300 rpm to 6100 rpm.

The better breathing and engagement-on-demand characteristics of the supercharger have not turned the engine into a polluting and thirsty monster. Mercedes-AMG engineers are proud that that the C 32 AMG has a NEDC combined fuel consumption of just 11.5 litres/100 km and already complies with the EU 4 emissions standard that does not come into effect until 2005.

The engine also develops the quoted performance figures on 'only' 95 RON fuel...

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