Fuel injection
The most notable change of the RC45 when released was the use of Programmed Fuel Injection. Fuel injection had been used on bikes previously but these had either been rather antiquated analog computers or very simple digital units with a minimal number of sensors for input, which resulted in very crude fueling. The RC30 had used 38 mm constant velocity carburettors which, for road use are quite nice, maintaining a high air velocity across a wide rpm range, though were not as well suited for racing. The RC45 did away with carburetors and in their absence a brace of four 46 mm throttles were replaced, Honda now had the throttle area it needed to make big horsepower at high revolutions. The system Honda used on the RC45 was very similar to the system used on the NR750. Contrary to popular belief the RC45’s fuel injection is not like a 4-stage carburetor, rather it is a proper fuel only system. Honda kept the ignition system separate. The Honda system obtained information from the following sensors: crankshaft position sensor, camshaft position sensor, air temperature sensor, coolant temperature sensor, manifold absolute pressure sensor, throttle position sensor, barometric sensor and battery voltage. With all of these sensors relaying information to the ECU, Honda could have quite easily incorporated the ignition control unit. The reason that they had not came down to the supplier of parts: they had different manufacturers supplying the ecu and cdi units. Regardless, it allowed the use of very large throttle plates seamlessly over a very wide engine operating range. The engine of the RC45 also used many magnesium castings, as of rather recently, it has become quite common to see fuel injection and magnesium engine parts on motorcycles, though in the early-to-mid 1990s this was expensive and incredibly innovative.