320 CDI vs 350 - Mercedes-Benz Forum
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post #1 of 2 (permalink) Old 05-03-2005, 07:56 AM Thread Starter
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Date registered: May 2004
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320 CDI vs 350

Hello,

I will do with this car 10000km/year; my other car is a Sportcoupe Brabus K3 with 230Hp.

I will buy the ML full loaded (all the extras minus the incompatible).

The prize of the 320CDI and the 350 here is exactly the same.

In my opinion right now the 320CDI has the advantage of more torque at lower rpm, best mpg(but I do few KM), 510nm; and the 350 has de advantage of 50Hp more and the sound of a gas engine.

Help me to choose.

Quote:
ML 320 CDI
Output: 200 kW/272 hp
Max. torque at rpm: 350 Nm 2400-5000 rpm
0–100 km/h: 8.4 s
Max. speed: 215 km/h
Fuel consumption: 11.5 l
Quote:
ML 320 CDI
Output: 165 kW/224 hp
Max. torque at rpm: 510 Nm 1600-2800 rpm
0–100 km/h: 9.4 s
Max. speed: 210 km/h
Fuel consumption: 9.4 l




Quote:
ML 320 CDI

Cylinder arrangement V6
Valves per cylinder 4
Displacement 2987 cc
Bore/Stroke 83/92 mm
Compression ratio 18 : 1
Output 165 kW/224 hp at 3800 rpm
Max. torque 510 Nm at 1600-2800 rpm


The world’s first aluminium V6 diesel engine

More output, more torque and lower exhaust emissions – the engineers at Mercedes approached the main objectives of their development work in various ways. Take lightweight construction, for example: owing to an intelligent choice of materials and innovative production methods, the DIN weight of the unit has been reduced to approx. 208 kilograms or roughly the level of the in-line five-cylinder. The power-to-weight ratio of the V6 engine is a remarkable 0.79 kW/kg.


As a world first, Mercedes-Benz has developed this diesel engine with an aluminium crankcase and cast-in grey iron cylinder liners. It tips the scales at only 41 kilograms and is therefore a prime example of lightweight construction. Aluminium is also used for the cylinder heads, cylinder head covers, pistons, coolant pump, sump and charge pressure distributor. Plastics are also used to save weight. Components in the fresh and charge air ducting systems, silencer and engine shrouding are of plastic.

A likewise newly developed valve control system reduces both friction and moving masses: the 24 intake and exhaust valves are controlled by an overhead camshaft for each cylinder bank, via roller-type rocker arms with hydraulic valve clearance compensation. The camshafts are driven by a tried-and-tested double-bush timing chain system into which the balancer shaft and the high-pressure pump for the fuel injection system are integrated.

Compact dimensions thanks to a new "one-box" design

Thanks to a newly developed "one-box" design, the V6 engine is among the most compact diesel power units in its displacement class worldwide. "One-box" design means that the engine forms a single, compact entity with its components and ancillary units. The complete air filter system is directly attached to the engine and therefore occupies no additional installation space. This makes the new V6 even more compact than the previous five-cylinder in-line unit.


In addition to lightweight construction, compact dimensions and low-friction valve gear, the new CDI six-cylinder would not be a Mercedes engine if it did not also meet the strict standards of the brand in terms of rigidity, vibration characteristics and long-term durability. Calculations and computer simulations provided the engineers in Stuttgart with valuable data and helped them achieve the demanding specifications. A look at the interior of the V6 engine:


The forged crankshaft rotates in four bearings which have been enlarged by five millimetres compared with the in-line six-cylinder unit in the interests of vibration comfort. The radii of the crank pins have been rolled to achieve high strength. The flexural and torsional rigidity of the crankshaft is more than twice that of the preceding engines.


The connecting rods are also of forged steel. Mercedes engineers have further optimised their weight by using a new alloy and making improvements to their geometry.


Careful design of the combustion chamber geometry, which includes the precisely calculated recesses in the piston crowns, optimises the combustion process and helps to achieve a lasting reduction in untreated emissions.


The free vibrations which are inherent to a V6 engine are compensated by a balancer shaft between the cylinder banks. This counter-rotates at the same speed as the crankshaft.
Heat exchangers for oil cooling, heating and exhaust gas recirculation

A separate roller chain is used to drive the oil pump. Via a large full-flow oil filter, the efficient and quiet external-gear pump delivers the oil to the oil-water heat exchanger located between the cylinder banks. The high 15-kW output of the heat exchanger ensures that even under extreme engine loads, the oil temperature does not rise above 130 degrees Celsius. The tunnel of the balancer shaft also serves as the main oil duct from which the oil flows to the main bearings, into the cylinder heads and to the piston-cooling spray units, which automatically open at a certain oil pressure and cool the pistons.


The mainstay of the water cooling system is a belt-driven pump on the crankcase. This is a double-helix pump which forces the coolant into the cylinder banks within the crankcase from the front, where it mainly flows to the exhaust side via special holes drilled in the cylinder head gasket. Cooling is thermostat-controlled on the cross-flow principle.

The flow of coolant for the oil-water heat exchanger comes from the crankcase on the right, while the exhaust gas recirculation (EGR) cooler and the heat exchanger for the heating system are supplied with coolant from the left cylinder head. The coolant circuit is therefore designed to ensure adequate heat dissipation under any load and engine speed conditions. Particularly high rates of flow are achieved at the valve lands, around the injector ducts in the cylinder heads, in the oil-water heat exchanger and in the exhaust gas recirculation cooler, enabling an efficient heat transfer to take place.

Turbocharger with variable nozzle turbine

The new V6 diesel engine is aspirated by a VNT turbocharger (Variable Nozzle Turbine). This technology already enables high levels of output and torque to be achieved at low engine speeds. Thanks to electric control, VNT turbochargers are able to vary the angle of their turbine blades rapidly and precisely to suit the operating status of the engine, and can therefore use the largest possible volume of exhaust gas to compress the intake air and build up charge pressure. At low engine speeds the turbine blades reduce the flow cross-section to increase the charge pressure, while the cross-section is enlarged at high engine speeds to reduce the speed of the turbocharger. More efficient cylinder charging and therefore higher torque are the results of variable, demand-related turbocharger control. Moreover, electric VNT technology allows a precise interaction with other units which are responsible for reducing untreated emissions and exhaust gas aftertreatment.


The turbocharger is combined with a downstream intercooler which reduces the temperature of the compressed, heated air by up to 95 degrees Celsius, allowing a larger volume of air to reach the combustion chambers. Behind the intercooler there is an electrically controlled flap which enables the V6 engine to be throttled back precisely when the exhaust gas recirculation is in operation. This electrically regulated control flap allows the volume and mix of the exhaust gases added to the combustion air to be very precisely metered. To optimise the volume of recirculated exhaust gas, it is abruptly cooled in a high-performance heat exchanger. Acting in conjunction with the hot-film air mass sensors integrated into the intake air ducts, which provide the engine control unit with precise information about the current volume of intake air, this significantly reduces nitrogen oxide emissions.


The combustion air then flows into the charge air distribution module, which supplies each cylinder in equal measure. The distribution module features an integral, electrically controlled intake port shut-off function with which the intake post cross-section for each cylinder can be variably reduced. This modifies the swirl of the combustion air, ensuring that the charge flow to the cylinders is adjusted for the best possible combustion and exhaust emissions under any load and engine speed conditions.

Piezo-ceramics for precisely metered injection within microseconds

The third generation of the well-proven common-rail direct injection system is entering series production at Mercedes-Benz with the new V6 diesel engine. This means that the injectors, high-pressure pump and electronic engine management system will operate even more efficiently, with a further reduction in fuel consumption, exhaust emissions and combustion noise.


Instead of the previous solenoid valves, the injectors are equipped with piezo-ceramics whose crystalline structure changes within milliseconds under an electric voltage. The engine developers used this effect, which was discovered in 1880 by the brothers Pierre and Jacques Curie, to lift the needle jet at the tip of the injector with a precision of mere thousandths of a millimetre and thereby achieve an extremely fine jet of fuel. Moreover, piezo injectors are considerably lighter and operate at twice the speed of conventional solenoid valves. With a response time of only 0.1 milliseconds, the fuel injection process can be even more precisely suited to the current load and engine speed situation, with favourable effects on emissions, fuel consumption and combustion noise. The number of fuel injections per power stroke is increased from three to five thanks to this piezo technology.

Mercedes engineers have also made improvements to other components of the common-rail system and the injection process:


The hydraulically optimised injector nozzles have eight holes (previously seven), which ensures even finer distribution of the fuel within the combustion chamber and more efficient mixture formation.


The inlet-metered high-pressure pump operates with a maximum injection pressure of 1600 bar.


The pilot injection process developed by Mercedes-Benz, which ensures a smoother combustion process and thereby audibly reduces the operating noise of the engine, takes place twice in succession in the new V6 engine. Small pilot quantities of fuel are injected within less than a millisecond and preheat the combustion chambers even more efficiently.


To burn off the soot particles in the particulate filter, there is a double post-injection of fuel when required.
Emission control with two catalytic converters and a particulate filter

Two oxidising catalytic converters clean the exhaust gases emitted by the new Mercedes diesel engine. One acts as pre-catalytic converter, and is ready for action very soon after a cold start thanks to its position close to the engine. This unit is accompanied by a downstream main catalytic converter. The purpose of the oxidation-type catalytic converters is to convert carbon monoxide and unburned hydrocarbons by combining them with oxygen to form chemical compounds (oxidisation).


This efficient exhaust gas aftertreatment combined with the complex in-engine measures already enables the V6 diesel engine to meet the stringent EU4 exhaust limits.


To lower exhaust emissions even further, Mercedes-Benz combines the new six-cylinder powerplant with a maintenance-free particulate filter system (standard in Germany), leading to a further significant cut in particulate emissions. The particulate filter regenerates itself without the use of additives and remains effective over a very high operating mileage.

ML 350 with a new 200 kW/272 hp six-cylinder engine

Output, torque, fuel consumption, comfort and exhaust emissions – these were also task areas of equal importance when developing the new V6 petrol engine. This up-to-date six-cylinder unit makes its mark in each of these disciplines. It offers technical innovations which do not just represent stand-alone solutions, but rather have a positive impact across a number of areas.


The Mercedes engineers had already created important conditions for an exemplary performance curve with four-valve technology and four overhead camshafts, but this was not yet enough for them. In addition they developed a system by which the interaction of the 24 valves can be controlled as required – depending on the engine load – while ensuring an extremely rapid gas cycle in the cylinders: continuously variable camshaft adjustment. This means that the angles of both the intake and exhaust camshafts can be continuously varied by 40 degrees, ensuring that the valves open or close at the best possible moment in any driving situation.


Under low engine loads the engineers have used this technology to allow the exhaust gases to flow directly from the combustion chamber and back to the intake duct: during the process the camshafts are adjusted so that the exhaust valves remain open for a short time while the intake valves are opening. During this split second, some of the exhaust gases are able to flow from the exhaust duct to the intake duct. The vacuum pressure in the intake manifold assists this process.


This valve overlap when venting the exhaust gases and taking in the fresh mixture makes an efficient internal exhaust gas recirculation possible. This reduces the energy losses during the charge cycle in the cylinders, leading to a significantly lower fuel consumption.


Under higher engine loads the camshaft adjustment feature is also used to optimise the valve overlap in line with the engine speed so that the combustion chambers are efficiently supplied with fresh mixture – which makes for a high power and torque output.

ML 350

Cylinder arrangement V6
Valves per cylinder 4
Displacement 3498 cc
Bore/Stroke 92.9/86.0 mm
Compression ratio 10.7 : 1
Output 200 kW/272 hp at 6000 rpm
Max. torque 350 Nm at 2400-5000 rpm


The V6 developers devoted a great deal of attention to anything that would contribute to optimal aspiration. Sophisticated computer programmes were used to calculate airflows, e.g. helping to optimise the flow of air from the twin-chamber air filter. This is where the ducts interface with the hot-film air mass sensor (HFM). The housing of this unit is oval in shape for optimal flow characteristics and accommodates an electrically heated sensor element which measures the flow of intake air, providing the engine management system with important basic information for the composition of the combustion mixture.


An intake module produced in well-proven magnesium technology enables the air intake to be varied according to the engine load and rev speed. The length of the intake pipes leading to the cylinders is varied by means of flaps. At high engine speeds – from approx. 3500 rpm – the flaps are open and the air takes the shortest distance to reach the combustion chambers, producing a high engine output. At low engine speeds the flaps are closed, increasing the length of the intake duct. This creates pressure waves which assist the intake process and fundamentally improve the torque generated in the lower engine speed range. No less than 305 Newton metres are already available from 1500 rpm, which corresponds to approx. 87 percent of the maximum torque.

Tumble flaps in the intake ducts

Electro-pneumatically driven flaps at the end of each intake duct are the special feature of the intake module in the Mercedes six-cylinder engine. These make a significant contribution to fuel economy. Mercedes engineers refer to these as tumble flaps, which in some measure indicates their purpose: they literally cause the fuel/air mix to tumble, increasing the turbulence of the airflow and causing it to enter the combustion chambers at higher speed, with a more uniform distribution. The result is better, more complete combustion.


At partial throttle, the tumble flaps pivot upwards, optimising the airflow and increasing the speed of combustion – an advantage that makes itself particularly noticeable in terms of fuel economy where the mixture is lean as a result of exhaust gas recirculation. Under higher engine loads the tumble flaps are not required, and can be completely recessed into the intake manifold so as not to impede the intake process. Situation-related control of the tumble flaps is based on stored characteristic maps.


By virtue of the tumble flaps in the intake ducts, the fuel consumption of the V6 engine can be reduced by up to 0.2 litres per 100 kilometres depending on engine speed – while improving smoothness at the same time.

Aluminium crankcase and cylinder head

The cylinder head and crankcase of the new V6 engine are of aluminium. The pistons, connecting rods and cylinder liners are produced according to the latest design principles, which not only contribute to weight reduction but also have a positive effect on engine responsiveness and smooth running. For the lower the moving masses in the crankcase, the lower the vibrations and the more responsive the engine becomes to movements of the accelerator pedal:


The pistons are of iron-coated aluminium. Taking into account the valve angle (28.5 degrees), the piston crowns are designed to ensure a favourable combustion chamber shape.


Mercedes engineers have been able to reduce the weight of the forged steel connecting rods by approx. 20 percent compared to other V6 engines, thereby making a significant contribution to the extreme smoothness of the new six-cylinder power unit.


The cylinder liners benefit from low-friction surfaces featuring aluminium-silicon technology which have also proven their worth in other Mercedes-Benz car engines. Other advantages include minimal distortion, exemplary thermal flows and low weight. The weight saving compared to conventional cast-iron liners is approx. 500 grams per cylinder.


The forged crankshaft is equipped with four counterweights. Four wide crankshaft bearings attached to the crankcase by transverse reinforcing struts also contribute to reduced vibrations.


A balancer shaft between the two banks of cylinders compensates the free vibrations inherent to a V6 engine and ensures exemplary smoothness. It counter-rotates at the same speed as the crankshaft.
Emissions control using in-engine measures and catalytic converters

The emission control system follows a two-stage concept: it is based both on sophisticated engine-specific measures for a reduction in untreated emissions and on highly effective emission control using two catalytic converters located close to the engine with a volume of 1.3 litres each. Each of these is equipped with two oxygen sensors – a control sensor and a diagnostic sensor – with linear control. This means that the oxygen sensors are already active immediately after a cold start, supplying information about the exhaust gas constituents for the electronic engine management system to process when controlling the warm-up phase.


The engine-specific measures include e.g. variable camshaft adjustment, which makes efficient internal exhaust gas recirculation possible under partial load. In the same way the adjustable tumble flaps in the intake ducts, which improve the combustion process, make an important contribution to minimising the untreated engine emissions. A secondary air injection system is also used. This has an afterburning action on the exhaust gases, increasing the temperature in the exhaust ducts and enabling the catalytic converter to start converting the pollutants at an earlier stage. During this afterburning process the carbon monoxide and hydrocarbon content in the untreated exhaust gases is also reduced.
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post #2 of 2 (permalink) Old 05-03-2005, 03:36 PM
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Date registered: Aug 2002
Vehicle: '12 Peugeot 3008 HYbrid4 (sorry!)
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RE: 320 CDI vs 350

Hi,

Based on experience with the W163, there's no doubt in my mind - get the 320CDI. On a number of rather steep motorway inclines, the W163/320 switched irritatingly between 4th and 5th to keep a constant speed. The W163/270 just barely changes engine note.

Of course, your local road taxes may influence on the choice. Reveal in which (Euraopean) country you're located, and you might get a more accurate help in choosing.

Birger
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