POWER COMMANDER
It's expensive but it will add power and improve throttle response. Or will it? And does your bike need it? Here's the low-down on that little black box
Most modern bikes come with electronic fuel injection (EFI). It works like this: an on-board computer (the electronic control unit, or ECU) gathers information from a number of sensors that detect factors such as throttle position, crank and cam position, air temperature, engine temperature, intake air pressure and atmospheric pressure. The ECU then refers to a table of pre-programmed injector settings in its memory (the 'map') and sends a signal to the bank of injectors telling them exactly how much fuel to deliver to the throttle bodies, where it mixes with air before entering the cylinder. The fuel/air mixture determines how well the engine runs. A rich mixture (too much fuel) means unburned fuel will go to waste in the exhaust gases, while a lean mixture (too little) means the engine will run hot, lose power and possibly melt and wear engine internals (fuel helps cool valves, cylinders and pistons). For complete combustion the fuel/air ratio must be around 14.7:1 - that's 14.7lb of air to a pound of petrol. But complete isn't always best. Optimum combustion produces maximum power and is achieved with a slightly rich mixture (up to 10% air deficiency), while a slightly lean mixture (up to 10% air surplus) will give the best economy. The optimum fuel ratio sits between 12.8:1 and 13.2:1, but manufacturers have parameters to account for.
A standard fuel map must operate within legal emissions limits. And because a rich mixture flattens the exhaust note, some bikes run rich where the noise test is carried out. This means many injected bikes will have a rich mixture-induced glitch at around 5500rpm. Original maps also allow for differences in manufacturing tolerances, so the fuelling has to work both on a worst and best-case standard engine. They must also take into account engine life (which extra power and cylinder pressures might reduce) and the poorest quality fuel likely to be used.
Dynojet's Power Commander is a plug-in device that overrides the original map either to compensate for changes to the bike or just improve on the standard map - there's usually scope for doing so even without making any other changes, given the regulations manufacturers are forced to comply with.
Creating a new fuel map is a painstaking exercise that involves sticking the bike on a dyno and working through the rev range incrementally by rpm and throttle opening, adjusting the fuelling first at standard atmospheric temperature and pressure (STP). Algorithms (think back to those large books of numbers from school that translated into flow charts and computer programmes) also have to be utilised to alter the fuelling when the engine is accelerating rather than being held at constant rpm, deal with that stutter problem from closed throttle to open, and soften the power delivery as you open the throttle to make the bike more controllable.
A properly-fuelled bike can be a joy to ride and a night-and-day transformation compared to the standard set-up, but bear in mind that the improvements to a remapped engine may not be to everyone's tastes. The more precise fuelling and instant throttle response of a well set-up Power Commander can be in marked contrast to the relatively woolly response that comes as standard. Ideally remapping should be done on a dyno, by a trained operator and on an individual bike basis, but downloadable maps for specific bike and exhaust combinations are available on the internet.
POWER COMMANDER VERDICT
Results depend on a bike's standard set-up. Improvements can be dramatic or barely noticeable, so stick your bike on a dyno or get a feel for glitches before spending your hard-earned.
COST 1/5
EFFECTIVENESS 4/5
OVERALL 3/'5
