How the BMW R1250 variable cam engine works

BMW’s new 1,254 cc boxer engines will have variable cam timing, and this video shows you how the system works

BMW is adding more ccs to their flat twin/boxer engines, and all the (former) R1200 machines step into the R1250 era. The mills will gain an insignificant figure in weight but will be more powerful, but the biggest change the boxer engine receives is variable camshaft architecture.

Only a rumor weeks ago, this has become a certitude. The most recent animation from BMW depicts how the new 1,254 cc engine works, with a cool insight in the entrails of one of industry’s most successful platforms. The system is called Shiftcam and uses an actuator and a shift gate to switch between two different types of response.

BMW’s Shiftcam is triggered by the throttle valve position. Depending on the valve’s angle, the smart system engages a certain shift gate that moves the cam sideways to one of the two positions. When the throttle valve has a small opening, the engine enters a partial load mode, with the cams providing little lift for smooth power delivery.

As the throttle valve opens past a predetermined angle, the actuator shifts the gate to the other position, and, with it, the cam shaft. Valves will now reach their complete opening distance for full power delivery.

The biggest question is how smooth this transition will be. Honda’s VTEC system is renowned for the abrupt power surge generated when the engine opens all the valves, while Ducati’s Testastretta engines make the change almost seamlessly.

BMW’s new R1250 boxer will produce a peak torque of 143 Nm, with the power figure reaching 136 HP at its max, so the smoothness of the power delivery switching is rather crucial. Knowing how smooth the Germans’ R-machines have been for the past two decades, we can expect the new power plant to follow suit. Or will it?

READ MORE on BMW motorcycles: BMW G310RR prototype

 

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