The higher output rating can be attributed mainly to the use of a turbocharger with a variable nozzle turbine. The blades are adjusted via a logic-controlled electronic system, which significantly reduces backpressure as the engine nears its rated output. The adjustment of the blades also produces improvements in the build-up of charge pressure, which the driver senses in the form of increased responsiveness. Added to which, "turbo lag" is significantly reduced, thanks to an increase in the charge pressure at engine speeds under 1800 rpm.
Injection pressure of 1600 bar is another reason for the improved performance figures, with the necessary fuel injected at high speed through the small nozzle openings necessary to control emissions. Longer injection times would lead to a greater build-up of heat and thus less efficient combustion.
Despite the increased output and significantly more stringent emissions standards, the CDI engine is now even more efficient than ever. This has been achieved in part by reducing friction losses around the mechanical camshaft control and improving the efficiency of the high-pressure pump governing fuel supply. In a class-leading development, the CDI engine can be ordered with a catalytic converter near the engine and a large underfloor catalytic converter as an option to meet the EU4/III exhaust emissions standard. UK compliance will be confirmed closer to the vehicle's launch.
The diesel-powered variant of the Viano is fitted as standard with a six-speed manual transmission, with the V6 power units accompanied by a five-speed automatic transmission, which can also be ordered as an option for the diesel model.
The manual transmission has already proved particularly successful in Mercedes Benz passenger cars and its gear ratios have been optimally matched to the performance characteristics of the diesel models.
The automatic transmission – also an established star of the Mercedes Benz passenger car range – is electronically controlled and fifth gear has an overdrive ratio. The electronic control unit processes a range of different signals relaying information on the engine speed and torque, the position of the accelerator pedal, the kickdown switch and wheel speed. Shifting is calculated for extra comfort and measured according to the situation in hand. The electronics step in to prevent manual downshift if this would push the engine speed to excessive levels.
The manual and automatic transmissions are operated using an ergonomically positioned shift lever/selector lever located in the centre console of the cockpit area. The automatic transmission offers two additional safety functions: the ignition key can only be removed if the selector lever is in position "P" (parking lock) and the selector lever can only be moved from position "P" when the ignition is switched on and the brake pedal depressed.
The Viano, with its longitudinally mounted engine and rear-wheel drive, offers two major benefits over its predecessor model (laterally-mounted engine, front-wheel drive): improved traction regardless of the load on board and optimised passive safety - the front axle and front structure play an even greater role in energy absorption in the event of an accident. And that's not to mention the well-balanced weight distribution of 50:50 between the front and rear axles.
The front module features a MacPherson front axle. The load-bearing element is a subframe with a lightweight sheet steel construction, which absorbs the wheel location forces through the wishbones. The subframe also boasts effective deformation properties, helping it to aid energy absorption as well. Linked directly to the suspension strut and attached to the subframe is a torsion bar stabiliser which is matched to the different vehicle variants.
The driven diagonal swing rear axle comes as standard with steel suspension, whilst the AMBIENTE equipment line is delivered from the factory with the extra comfort of self-levelling air suspension on the rear axle. This construction can be ordered as an option for the other models and also features a rear-axle torsion bar stabiliser.
The Viano is fitted as standard with 6.5Jx16 wheels with 205/65 R 16 tyres. The AMBIENTE model leaves the factory with light-alloy wheels in the same dimensions. 225/60 R 16 tyres are available as an option for the light-alloy wheels and 7Jx17 light-alloy wheels with 225/55 R 17 tyres can also be fitted on request. In the event of a puncture, the compact Viano comes as standard with the TIREFIT system, complete with electric compressor. A full-size spare wheel is standard on long and extra long models.