Dual Stage Programmed Fuel Injection

The blink of an eye takes about one-quarter of a second, or 250 milliseconds. At 15,000 rpm, each intake and exhaust valve of Honda's CBR600RR opens and closes 125 times a second, or 8 milliseconds. That means the valves will open and close 31 times before the rider can even blink.

More importantly, at 15,000 rpm there's only 4 milliseconds for the fuel squirting out of the Denso injectors to vaporize and combine with incoming air into a combustible mixture; fuel droplets simply do not burn well. The RR's engine demands at that rpm exceed the capabilities of conventional fuel delivery systems, however sophisticated--there's just not enough time.

In Formula 1, the successful answer was to place a second injector as far from the intake valve as the length of the intake tract would permit. This so-called showerhead injector, positioned over the open end of each velocity stack, injects fuel at higher rpm. Its greater distance from the cylinder provides extra vaporization time, plus exposure to the turbulent mixing of the intake flow. It also significantly cools the airflow, resulting in a denser charge that yields more horsepower.

Honda incorporated such a system on its RC45 Superbike machines, and more recently on the world-championship-winning RC211V. The same concept drove the design of the CBR600RR's fuel delivery, its Dual Stage Fuel Injection System (PGM-DSFI). On the RR, this advanced system utilizes a set of four 12-hole fuel injectors mounted in new, larger 40mm throttle bodies, plus another full set of 12-hole injectors mounted high in the roof of the airbox. At higher engine speeds--5500 rpm and above--the showerheads deliver fuel just a fraction of an instant before the main throttle-body-mounted injectors do. Because of the conventional injectors' proximity to the intake valves, the CBR600RR's throttle response is razor-sharp below 5500 rpm. Combined with the airbox-mounted showerheads, the RR continues to deliver incredibly strong power all the way to its stratospheric, 15,000-rpm redline.

To ensure the RR's Dual Stage Fuel Injection System has sufficient computing power to take care of the engine's needs at sky-high rpm, Honda has fitted a new 32-bit-processor ECU. The new ECU provides phenomenally higher-speed operation and accuracy for optimum performance throughout the engine's rpm band. Engine rpm and throttle angle--n-alpha--control how, when and how long the injectors fire. As with other Honda fuel injection systems, the RR's PGM-DSFI includes an automatic cold-start and warm-up enrichment system, which eliminates a conventional manual choke/enricher control, and provides smooth, crisp throttle response right from start-up.

And it all happens before you can even blink your eye.

  • share: