Q What does Shiftcam really do?
An engine’s state of tune, both in terms of its physical components and the electronic control of fuelling and ignition, is usually a compromise between economy, emissions and performance. Shiftcam technology lets BMW’S 1250 alter its physical characteristics while running, from low-performance, low-emissions and higheconomy to higher performance, higher emissions and lower economy.
It does it by, literally, shifting cams. A cam – or more accurately, a cam lobe – is an egg-shaped part of a rotating shaft (called a camshaft) which forces an engine valve open. On one side, the valves let air and fuel in (inlet) and the other, burned gasses out (exhaust).
What’s important is when, for how long and by how far the valves open — timing, duration, and lift respectively — and it’s governed by the size and shape of the cam lobe – its profile.
A lobe with a tiny (mild) profile will open the intake valves a small amount and not for long, and you’ll likely have an engine that’s clean and economical, but with low performance. Open the valves further and for longer with a moreaggressive profile and you may have more performance but a dirtier and thirstier engine.
A cam lobe profile is fixed. But BMW’S Shiftcam has two cam lobes per inlet valve, and the camshaft is moved back and forth, mechanically, to engage one or the other depending on whether the rider opens the throttle wide and asks for performance or cruises on light throttle for economy. That’s the theory. Does Shiftcam succeed? It’s hard to tell. Partly because you can’t feel it working on the bike — there’s no physical sensation when the cam switches between lobe profiles — and partly because BMW has enlarged the new engine by 84cc. So when you study a dyno graph, a performance figure or just ride the bike, the extra capacity tends to mask other engine modifications. The probable truth is Shiftcam helps spread torque more evenly across the rev range and the engine should theoretically be more fuel efficient and cleaner than it would be without it. But the only way to tell for sure would be to take the same engine and disable Shiftcam — any volunteers?