2008 BMW HP2 Sport - First Ride

DOHC, Radial Valves And 133 Horsepower Make This The Sportiest Boxer Ever

By Alan Cathcart, Photography by Kel Edge, Courtesy of BMW

2008 BMW HP2 SportHard Parts A Look Under The Skin Of The Sportiest Boxer Ever
Ultra-light PvM forged-aluminum wheels, with the same spoke pattern as the endurance racer, carry Metzeler Racetec tires and Brembo brakes. Twin 320mm front discs are gripped by four-piston, two-pad Monobloc calipers that are radially mounted (for the first time ever) to the Telelever sliders. The 265mm rear disc, meanwhile, is paired with a twin-piston caliper. BMW's signature ABS is an option, with the ability to switch the system off for racetrack use.

The fuel-injected, 1170cc flat-twin is essentially identical to that of the company's world endurance racer, with the same 101 x 73mm cylinders and DOHC, four-valve heads that do away with the boxer's venerable pushrods. The cams are chain driven and operate 39mm intake valves (3mm larger than before) and 33mm exhaust valves (2mm larger), which are arranged radially at an angle of 11 degrees. The improved breathing, optimized combustion and enhanced mixture swirl that the radial valves deliver mean that the standard R1200S Twin Spark ignition is no longer needed. Forged Mahle high-compression (12.5:1) pistons paired with uprated steel connecting rods round out the upgrades to the reciprocating parts. On the fueling front, a Bosch BMS-K ECU controls a single injector in each 52mm Dell'Orto throttle body, actuated by the same variably progressive butterfly linkage as on the R1200S. Twin, stacked oil coolers mounted in the nose of the bike control temperatures and a deeper, finned sump minimizes sloshing under heavy braking or acceleration. Twin, gear-driven counterbalancers smooth out the secondary imbalance of the 180-degree crankshaft and the complete engine weighs just 101 lbs.-much lighter than any water-cooled v-twin. A Euro 3-compliant, stainless steel, underseat exhaust (with single catalyst) is now routed beneath the sump to provide additional cornering clearance. An ECU-controlled, cable-actuated power valve broadens the torque curve, and twin oxygen sensors (one in each head pipe) help regulate the mix. This street-legal engine delivers 133 bhp at 8750 rpm-just 7 bhp down on the racer (due to the more-restrictive exhaust) and a useful 11 bhp up from the 122-bhp R1200S.

The Telelever front end consists of Marzocchimade telescopic struts held in special triple clamps milled from aluminum billet, acting on a fully adjustable hlins shock that now includes the compression-damping adjustment lacking on the R1200S. The single-sided, shaft-drive Paralever rear end is identical to that of the R1200S, and works on a fully adjustable, cantilevered hlins shock. Both suspension units are 20mm longer than the R1200S's WP components to increase cornering clearance.

The flat-twin engine acts as a fully stressed chassis member. The main frame section and the front subframe are constructed from tubular steel; the rear subframe is a selfsupporting carbon-fiber component that weighs just 4.9 lbs.-4.4 lbs. less than the aluminum rear subframe on the R1200S. Sophisticated ducting incorporated into this subframe/seat unit assists with heat dispersal around the underseat muffler.

The close-ratio, six-speed Getrag tranny utilizes slightly higher first- and second-gear ratios than the standard R1200S. Helical-cut gears are retained for slicker, quieter operation, and a Formula 1-derived sleeve-and-roller selection system replaces conventional shift forks. For the first time ever on any production streetbike, a quick-shifter is fitted to the HP2 Sport to allow wide-open, clutchless upshifts by momentarily cutting both spark and fuel supply when the shift lever is loaded. The rider retains the option of changing gears conventionally, simply by using the clutch lever to hydraulically operate the single-plate dry clutch.

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