Monday, May 23, 2016

Time is running out for Bentley’s 6.8-liter V-8, but not in a hurry

2015 Bentley Mulsanne Speed twin-turbocharged 6.75-liter V-8 engineWith torque characteristics and a soundtrack reminiscent of an ocean liner’s steam engine, the Bentley Mulsanne‘s venerable 6.8-liter V-8 is a one-of-a-kind powerplant. But the 57-year-old engine, which the company calls a “6 3/4 Litre” won’t survive beyond the current Mulsanne, we are told by Bentley CEO Wolfgang Dürheimer, who says that the V-8 has found “its final home” there. He confirmed that the next generation of Bentley’s flagship would be powered by a 12-cylinder engine, but didn’t pin down a timeline for that car’s introduction.

If Bentley seems to be in no hurry to shed this key attribute of its heritage, it has also been clear for years that one of the industry’s most enduring powerplants couldn’t last much longer; now time seems to be ticking down to the end. Known as the L-series, the V-8 was launched in 1959 and subsequently used by generations of Rolls-Royce and Bentley models, it appeared that BMW had finally killed it off in the late 1990s, when it replaced the engine with a BMW-derived 4.4-liter V-8. At the time, Munich was already asserting that it wasn’t worth updating what was then a 40-year-old design to meet ever-stiffening regulations requirements for emissions and fuel economy. But just a year later, VW took over and humbled BMW by re-introducing the L-series engine under the “Red Label” moniker. The BMW engine, christened “Green Label,” sold so poorly that it was discarded shortly thereafter. (It wasn’t good enough for BMW-owned Rolls-Royce, either, where V-12s now power everything).

Mulsanne Speed V-8 NewsThe big powerplant, like the Chevy small-block V-8 that traces its origins four years farther into the past, has undergone significant re-engineering along the way. The bore center spacing is the same as on the original dual-carburetor 6.2-liter version that launched in the 1959 Bentley S2 and Rolls Royce Silver Cloud II, but the block (always aluminum) has undergone redesigns to stiffen the bottom end, the pushrod valvetrain now employs cam phasing to vary the timing of the pushrod-operated valves, there’s cylinder deactivation to shut down four cylinders under light loads, and turbocharging arrived as far back as 1983. With twin turbos and a new cylinder head design introduced in 2015, today’s port-injected L-series engine boasts 530 horsepower and a locomotive-like 811 lb-ft of torque at only 1750 rpm in the Mulsanne Speed.

The L-series engine should not be confused with the modern 4.0-liter dohc V-8 design Bentley offers in the Flying Spur and the Continental GT. The engineering world isn’t entirely out of tricks that could still be applied to Bentley’s aged pushrod lump—General  Motors uses direct fuel injection in its latest small-block V-8 and the Dodge Viper V-10 employs more exotic cam-in-cam technology to allow wider variation of valve timing—but Durheimer’s statement suggests his company is done spending to modernize its L-Series. It’s still got some years to run, though. With the Mulsanne just updated for 2017, it appears its replacement could be 5 years away yet.


from Car and Driver Blog

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