Fuelling about with maps

Selecting a power mode on your bike? The future’s already been mapped out. Literally.

Fitting a litre sportsbike with a castrating low power engine mode sounds like a bad idea, even if you call it ‘Rain’ mode. And few electronic aids are as contentious because engine modes are, technically, voluntary restrictions. Each is, broadly speaking, an overlay of instructions directing the ECU to manipulate and reduce engine performance.

But what actually happens when you push that button? The story starts with an ECU fuelling map. Imagine a blank graph on which the X-axis is rpm, and Y-axis is engine load. All points are a combination of revs and engine load for which a development engineer has selected the ideal fuel injection settings (how long the injector fires; its pulse width) for a given target or permutation of power, fuel economy and emissions. He’ll perform this ‘calibration’ during engine development on a test-bench.
Now suppose the graph, or ‘map’ is actually 3D, with a third axis of ignition advance (as revs rise, ignition must start earlier in the stroke to maximise power and minimise emissions). The ECU now has a tri-axis map from which to select the target fuelling. And if the target is just high performance, that’s all the info it needs.

But modern engines must be useable, efficient and clean too (for 90 per cent of road riding most ECUs run a map prioritising emissions and putting a smooth engine and civilised throttle response a distant third equal).

Now it gets complicated. On new bikes, an array of sensors feed throttle position, ambient, coolant, oil and exhaust temperatures, manifold air pressure, exhaust gas oxygen content, crank speed, gear position, engine knock, wheel speed, brake pressure and traction control status into the ECU. From these multiple permutations (think of it as a huge data cloud) the ECU selects an appropriate, pre-programmed output: when to add fuel, for how long, how much air to mix it with (throttle position), and when to burn it. It’s a mathematical juggling act, carried out before the bike was built, then programmed into it.

Engine modes are a piece in this programming jigsaw: they’re a crude ECU setting, adjusted at the handlebars, to give us an engine strategy that boffins have chosen as the best for a given scenario. It may slow down or restrict throttle opening, reduce ignition advance in the midrange, or simply add less fuel. Or all of them, to varying degrees, at once. But it’s nothing an ECU doesn’t already do.

So surely it’s as daft to ignore an engine mode that makes, say, learning a new track in the wet a less fraught, as it is to rail against automatic exposure and shutter speed settings on a camera? You can have fully manual if you want; just sometimes it’s easier to switch to auto.

But then, why stop with different power modes? Who wouldn’t prefer a get-me-home engine mode that gives half the power but 30 per cent better fuel economy? Or a ‘dirty’ mode to enrich the mixture specifically at 80mph in top gear for a smoother engine cruising on motorways? Now those really do seem like good ideas...