Mercedes-Benz is extending its S-Class range with another diesel variant, the S 420 CDI. The new eight-cylinder model is powered by a 4.0-liter V8 CDI engine developing 235 kW (320 hp) of power at 3,600 rpm and 730 Nm (538 lb-ft) of peak torque from 2,000 rpm.
This latest addition to the model line-up means that the luxury sedan range from Mercedes-Benz now encompasses two diesel engines, six petrol models and two body variants, along with the new 4MATIC all-wheel-drive system. The new S 420 CDI is available to order now, with deliveries to customers due to start in December 2006.
The S 420 CDI powers from 0-100 kph in 6.6 seconds and has a top speed of 250 kph (155 mph), with fuel consumption figures of 9.4 to 9.6 litres of diesel per 100 kilometers on the NEDC cycle (24.5 to 25 mpg US).
That makes the S 420 the second-most fuel efficient vehicle in the S series, behind the V6 S 320 CDI, which, with 173 kW (235 hp) of power and 540 Nm of torque consumes between 8.3 to 8.6 l/100km (27.4 to 28.3 mpg US). The closest comparable gasoline vehicle in the series—the 4.7-liter V8 S 450 (250 kW and 460 Nm) consumes 11.2 to 11.5 l/100 km (20.5 to 21 mpg US) of fuel.
As another point of comparison, the hybrid powertrain in the Lexus LS 600h L combines a new 5.0-liter gasoline direct-injection V8 with large, high-output electric motors and a newly-designed battery pack to deliver more than 330 kW (442 hp) of total system power with fuel consumption of less than 9.5 liters/100km (more than 25 mpg US). (Earlier post.)
In the S 420 CDI, third-generation common-rail high-pressure injection technology with a maximum injection pressure of 1,600 bar and an ignition pressure of 175 bar contributes to efficient combustion. Optimized flow dynamics for the best possible gas cycle and twin turbochargers with variable-nozzle turbines support high power and torque delivery.
As many as five injections of diesel fuel per injection cycle, special orifice nozzles, piezoelectric injectors and highly effective exhaust gas recirculation all help to lower emissions significantly.
The new V8 powerplant is equipped as standard with a maintenance-free diesel particulate filter to cut untreated emissions even further, and also complies with the Euro 4 emissions standard. The engine development team was able to reduce noise levels by optimizing the chain drive and fitting a rigid crankcase with large engine bearings as well as extra acoustic covers. The square bore-to-stroke ratio combines with a counter-rotating balancer shaft for outstandingly smooth operation.
The engine is mated with a seven-speed automatic featuring a wide ratio spread.