Real world rides, real world riders

The Horex 1200 VR6: The full story

The bike was launched in Munich on 15 June as a clean-sheet design full of original thought that promises stellar performance in giving new life to one of Germany’s most significant forgotten marques.

With fresh but understated styling by Peter Naumann, hitherto best known as the creator of the edgy MZ 1000S, the new bike brims with innovation, and heralds a range of future spin-off models down the line, including a Café Racer, Tourer, Streetfighter etc.

Set to start production in Germany in October 2011, with a first batch of 150 bikes selling at the company’s announced target price of around £17,000 on the road, the 1200cc Horex VR6 Roadster has been unveiled as the fruit of five years of development, ever since company founder Clemens Neese, a mechanical engineer with 20 years of management experience in the IT industry which included working for Oracle in Silicon Valley, California, decided in 2005 to build a motorcycle incorporating a narrow angle V6 engine, like the VR6 motor used so successfully by Volkswagen. Neese has taken the precaution of patenting the engine format for two wheeled use, and has assembled a team of top technicians to create the world’s first series production supercharged (as opposed to turbocharged) streetbike, after sourcing start-up financing from a group of European investors which his partner Franz Fischer, the Horex CFO, says will see the project through to production.

Private investors

“In addition to our own significant investment, we're supported by the KfW Mittelstandsbank ERP programme, which specialises in equity and venture financing to business start-ups,” states Fischer. “We also have several private investors along with funding from the German Federal Ministry of Economics and Technology, so all in all, the company has a double-digit million-Euro budget to finance the project up until the market launch. This includes construction of a factory in Germany where the first series production models are scheduled for manufacturing starting in the last quarter of 2011.”

Remarkable

To develop the comeback Horex VR6 model, in 2005 Neese commissioned a former schoolmate of his, Martin Doll, now Professor of Internal Combustion Engine Design at Munich’s University of Applied Sciences, to design a motorcycle VR6 engine – and he’s done this in conjunction with Rupert Baindl, one of the most unconstrained and inventive motorcycle engineers of the modern era. Creator of the twin-crank four con rod radial-valve 1430cc parallel-twin turbo diesel engine in the Neander cruiser, and before that the European title-winning radial-valve BMR Supermono road racer, Baindl has brought a similar kind of innovation to the VR6 motor in the Horex. To develop this, he first constructed a 200cc single-cylinder slave engine, which allowed many different design strategies to be experimented with, and wound up producing a remarkable and very satisfactory 40bhp, says Baindl. “We should make a 250cc version, and offer it for the new Moto3 class when it arrives!” he jokes. Six times 200cc equals 1200cc, so this then formed the basis for the VR6 design, which came into being in 2008.

This measures 68 x 55mm for a capacity of 1218cc, and the narrow 15 degree included angle between its two banks of cylinders delivers what is in effect a space-saving staggered straight-six with a mirrored offset cylinder format – at 429mm wide, the VR6 motor is more narrow than many inline fours. The compact layout means that just a single cylinder head is employed, as on a VW VR6, saving on costs and complication and in turn dictating Horex’s patented tohc (triple overhead-camshaft) format that’s unique in modern motorcycle engineering, with all three cams driven via a composite system. This sees the front and centre camshafts chain-driven directly off the crank, with the rear camshaft gear-driven off the central one.

That centre camshaft operates the exhaust valves in the rear cylinder bank as well as the inlet valves in the front row of cylinders, with the rear camshaft taking care of the inlet valves for the rear cylinders, and the front counterpart the exhaust valves for the front bank.

Optimum combustion

The three valves per cylinder (two inlets and a single exhaust) are set radially to one another, and are operated by tappets, with a single injector per cylinder for the Bosch EFI. “It was important to have a central spark plug location for optimum combustion and to maximise power output,” says Martin Doll, “and with four valves per cylinder this was impossible, so rather than use dual ignition, we’ve chosen a three-valve format.”

Owing to the narrow-angle Vee formation of the cylinders, the Mahle forged pistons for the Horex engine are designed with slanted crowns, which allows for all six combustion chambers to be arranged on a single plane. To optimize power output, the symmetrical port configuration between the cylinder banks positions all six intake ports in two straight, parallel rows with a vertical downdraught intake for each that’s as direct as possible from the airbox centrally mounted above the engine. The air flows through a super-charger located behind the cylinder block via special channels integrated into the frame spars of the new Horex’s chassis.

There’s a single 50mm Bing throttle body housed inside the airbox to save space, which also eliminates any need for complicated and potentially troublesome balancing of six separate throttle bodies. This delivers mixture to the red-painted Danish-made Rotrex centrifugal supercharger located behind the cylinder block, which is chain-driven via an intermediate gear directly off the crank, and has an internal gearbox with a 12.7:1 ratio which gears up the supercharger to run at 180,000rpm. The centrifugal compressor was chosen for its quieter operation and more linear build of boost and torque compared to a positive displacement Roots type, says Prof. Doll [see Supercharger sidebar (Not on-line, in the magazine only)].

Rideable package

Running 1.45bar/21psi of boost with a 9:1 compression ratio and a thin airbox-mounted intercooler, Horex claims a massive 113ft-Ib of torque peaking at 7200rpm from the blown VR6 motor, but spread over a broad range of revs via a very flat curve, with peak power of 200bhp delivered at 8500rpm, and the design safe to 10,200rpm at present. “But the engine is extremely friendly in the way it delivers this,” says Doll. “It’s a very rideable package. However, we intend to introduce a variable boost system to the compressor, which will spread the benefits of the supercharging over an even wider range of engine speeds.” This will be controlled by the Bosch ECU, and will vary according to rpm, throttle position, and gear selected, while according to Prof. Doll, Horex is also working on a cylinder cutout system aimed at improving fuel consumption and reducing emissions, which deactivates two or three of the six cylinders in conditions such as city traffic, or when travelling at constant speed at part load on the freeway.

Faithful

“We will also consider different engine formats with more or less cylinders, while remaining faithful to the core VR concept,” he reveals. The six-speed gearbox with overdrive top gear transmits all that performance to the rear Metzeler Sportec M5 Interact tyre via a hydraulically operated oil-bath clutch and Gates Kevlar belt – the first time such a final drive choice has been used with such a high-performance engine. Top speed is limited to 250kph, as on all German-made vehicles, irrespective of the number of wheels.

This powerful, completely innovative motorcycle engine that’s inevitably quite heavy – Horex declines to reveal its weight – is housed in an equally unusual composite chassis comprising twin aluminium side spars attached to a tubular steel subframe incorporating the steering head.

Geometry

This modular design will allow steering geometry to be varied between 22º and 28º for those future variants on the Horex VR6 theme, with the wheelbase varying between 1475-1502mm as a result, and the Roadster sees black-painted 50mm upside-down Öhlins forks matched to a shock with progressive rate link from the Swedish sultans of suspension, operated via a bell-crank by the single-sided cast aluminium swingarm. This delivers space for the 6-1-3 catalyst exhaust to tuck its three megaphones in on the opposite side in what designer Peter Naumann calls “a gentle reminder of what this engine is”, with the distinctive H-shaped rear light another signature feature.

“When the new Horex goes on sale, we will have a solid network of qualified retail partners.”