Latest V8 and V6 Engines Feature Four-Valve Architecture

The 2007 model year marks the debut of a new Mercedes-Benz family of all-aluminium V8 engines featuring four-valve-per-cylinder technology and variable valve timing – first, a 5.5-litre delivering 382 horsepower and 391 lb.-ft. of torque in the new-generation S-Class sedan, followed by a 4.6-litre, 335-horsepower version in the new GL-Class sport utility. Beginning in fall 2006, the new 5.5-litre powerplant also replaced the previous 5.0-litre V8 in five other classes – the SL roadster, the CLS coupe, the E-Class sedan and wagon, the CLK coupe and Cabriolet, and the new-generation CL coupe.

In the 1990s, one of the most advanced engine technologies in the auto industry featured three valves per cylinder, in which a single exhaust valve kept exhaust temperature high and emissions low. In the ensuing years, Mercedes engineers have developed new ways to minimize emissions, allowing them to utilize higher-flow four-valve technology for the new engine family.

High-Tech V6 Powerplants, Too

The latest four-valve architecture actually made its debut on the Mercedes-Benz V6 that powers the new-generation SLK coupe/ roadster and is now available in three different sizes. The 3.5-litre V6 produces 268 horsepower and 258 foot-pounds or torque, with maximum torque available from 2,500 rpm all the way up to 5,000 rpm. In addition to the SLK coupe/roadster, the 3.5-litre engine powers the C350 and E350 sedans, the R350 luxury vehicle, the ML350 sport utility, and the CLK350 coupe and Cabriolet models.

In addition, a 228-hp 3.0-litre version of the new-technology V6 powers the C280 sedan, and the C230 sedan comes with a 201-hp, 2.5-litre version of the same basic engine.

Variable Intake and Exhaust Valve Timing

The latest Mercedes-Benz V6 and V8 engines make use of variable intake and exhaust valve timing to maximize efficiency and torque over a wide RPM range. Variable valve timing requires separate camshafts for the intake and exhaust valves, and valve timing can be automatically adjusted within a range of 40 degrees using electro-hydraulic vane-type adjusters on each camshaft. At part throttle, the valve timing adjuster keeps the exhaust valves open as the intake valves are opening, using this valve overlap for internal exhaust gas recirculation, reducing exhaust emissions and improving fuel economy. However, approaching full throttle, the camshaft adjustment optimizes valve timing for maximum power. To minimize disturbing air flow through the ports, valve stems are only six millimetres or about 1/4 inch in diametre (most valves have 7 or 8 mm stems), and the valves are angled at 28.5 degrees to optimize the combustion chamber shape.

Tumble Flaps Improve Fuel Efficiency

The engines are equipped with tumble flaps in the intake passages near the combustion chamber. The tumble flaps pivot open under part load, improving combustion by creating additional turbulence around the intake valve and in the combustion chamber. During higher engine loads such as full throttle, the tumble flaps are completely recessed in the wall of the intake manifold. Better combustion helps improve engine torque, but the primary purpose of the tumble flaps is to further increase fuel economy, and tests show that the tumble flaps indeed boost gas mileage by about two percent.

Two-Stage Intake Manifold Fattens the Torque Curve

While variable valve timing gets a lot of credit for the unusually broad torque curve of the latest engine architecture, a two-stage magnesium intake manifold plays a key role as well. At relatively low engine speeds, a set of flaps in the manifold close off short intake passages, forcing intake air to take a much longer route into the engine. This creates pressure waves that help the intake process and improve torque at lower engine speeds. Above about 3,500 rpm, the flaps open and intake air flows the shortest distance to the combustion chambers, helping to generate maximum horsepower, especially at higher speeds.

Assembling the Latest Mercedes-Benz Engine from Start to Finish

Whether it’s a new V8 or V6, the layout is nearly the same. A pressure-cast aluminium cylinder block uses innovative cast in silicon aluminium cylinder sleeves and low friction surfaces that allow very low piston ring spring tension. The sleeves are cast separately, but rather than being pressed into the block, the block is cast around them. In the process, the outer 20 percent of each sleeve melts, bonding each to the block. This process provides exceptional block stiffness while minimizing weight.

A forged crankshaft is placed into the engine block, which features wide main-bearing saddles and transverse bearing supports that minimize vibration. Iron-coated aluminium pistons are pinned onto forged steel connecting rods that are about 20 percent lighter than other comparable engines. The pistons slide into the cylinders, and the connecting rods are clamped around the crankshaft journals.

The two cylinder heads are bolted onto the block, and twin camshafts are installed in each head. The intake cams are driven by a double chain from the crankshaft, and small gears on the intake cams in turn drive the exhaust cams.

Double-wall exhaust piping is used to keep the exhaust air as hot as possible leading down to twin catalytic converters. With the help of secondary air injection, the catalysts promote additional downstream conversion of pollutants into carbon dioxide and water vapour, and two oxygen sensors for each catalyst monitor and help manage the entire process.

On the V6 engines, a balance shaft is added to the block to counter vibration that’s inherent to a 90-degree V6. The same duplex chain that drives both intake cams also loops under the balance shaft sprocket, so it counter-rotates at crankshaft speed. Located between the two cylinder banks (about where the camshaft would sit in a pushrod-type engine), its off-balance “lobes” are designed to cancel out vibration.

About Mercedes-Benz Canada

Mercedes-Benz Canada is responsible for the sales, marketing and service of the three brands within the Mercedes Car Group in Canada; Mercedes-Benz, smart, and Maybach. Headquartered in Toronto, Ontario, Mercedes-Benz Canada employs approximately 900 people in 18 locations across Canada. Through a nationwide network of 17 Mercedes-Benz owned retail operations and 39 authorized dealerships, Mercedes-Benz Canada sold 17,567 vehicles in 2006, the best year ever reported for Mercedes-Benz Canada Inc.

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