Berlin, Germany - BMW has been building flat-twin ‘Boxer’ engines since 1923 and, despite a valiant attempt to replace them with a weird inline flat four in the 1980s, the horizontal pots sticking out on either side of the frame are still the marque’s defining feature.
But that doesn’t mean BMW Motorrad’s technology has stood still over the years, with dual overhead camshafts, four-valve heads, liquid cooling and electronic fuel injection replacing the erstwhile airheads, pushrods and Bing carburettors.
But now the Blue Propeller Boykies have taken that progress one huge step further with the R1250 GS beetle-crusher and RT full-dress tourer, incorporating new variable-cam technology on the inlet side for a wider, smoother spread of power. However, to keep up with significantly more powerful adventure tourers from KTM, Triumph and Yamaha they first bored the cylinders of the current R1200 out an extra 1.5mm and increased the stroke by 3mm to increase its displacement from 1170cc to 1254cc.
Then they fitted new four-valve heads with dual overhead camshafts driven by a quiet-running Hy-Vo toothed chain, rather than the previous roller chain. The inlet cams can also slide sideways, controlled by a helical groove that looks just like a miniature version of the shift drum in a constant-mesh gearbox, varying both the timing and the lift of the inlet valves for improved breathing and precise throttle control (fly-by-wire, of course) across the rev range.
More than that, one inlet valve opens a little ahead of the other, to induce a classic ‘twin swirl’ in the combustion chamber for cleaner, more efficient running, together with twin-jet injectors and a new exhaust system.
The result is a nine percent increase in power, from 92kW to 100kW at the same 7750 revs, and a 14 percent increase in torque, from 125Nm at 6250rpm to 143Nm at 6500rpm. BMW doesn’t quote performance figures but experience leads us to expect a noticeably sharper midrange, a broader powerband, quicker acceleration and a top speed of around 210km/h for the R1250 GS, perhaps a little more for the R1250 RT tourer.