The straight-six is undeniably one of the most successful engine configurations in motoring history.
Think Mercedes-Benz, BMW, Jaguar, and here in Australia, Ford, and some years back, Valiant and Holden.
And while it has always been the dream of engineers to transplant the technology into bikes, it is something that few customers have ever warmed to.
The biggest issues with six-cylinder units have always been weight and size, off-setting any power advantages and disturbing weight distribution and centre of gravity.
But BMW Motorrad is having another go at it with the new Concept 6, technology that is set to make its way into the K-Series in the not too distant future.
BMW claims the engine is approximately 100 mm slimmer than all former straight-six production engines and only a bit wider than a large-capacity straight-four with conventional technology.
The reduction in width is achieved by the slightly over-square bore-stroke ratio with relatively long stroke and very small gaps between cylinders. To achieve the compact configuration the electrical ancillaries and their drive components are positioned behind the crankshaft in the open space above the transmission.
The two hollow-drilled camshafts and light connecting rods help to keep the weight down.
The straight-six featured in the Concept 6 follows the straight-four in the K 1300 model series, again coming with cylinders tilted to the front by 55-degrees.
The engine features with dry sump lubrication leading to greater reliability under extreme conditions and meaning the engine can be positioned lower than on a conventional layout.
Power output will be about the same as BMW's 1.3-litre straight-four power units, but torque is boosted to 130Nm and is available from 2000-9000rpm.
There is no word on fuel efficiency or emissions yet, but BMW says with a catalytic converter it is comparable to other four-cylinder units under touring conditions.
The design – with its long front end and short rear – draws on the legendary Cafe Racer, created with the engine at the heart to visible from every angle.
The Concept 6 also scores 17-inch HP forged wheels and six-piston fixed callipers to add to the sporting look.
The instrument panel is minimalist in design, but replaces the conventional rev counter with an LED display which shows the rider how much torque is available whenever required.
by Tim Beissmann