Using Endurance Racing to Go Full Circle

Honda goes racing to not only win championships, but to also accomplish the necessary research and development for a new 750.

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by Dain Gingerelli

Only a few years after the CB750 Four’s landmark 1969 debut, Honda Motor Co.’s movers and shakers determined that it was time for a replacement. The bike that had once rocked the motorcycle establishment with its single-overhead cam, 4-cylinder inline engine was growing long in the tooth. What to do, and in typical Honda fashion they did what they did best — they went racing, this time as much to develop a replacement product as to win championships.

And for 1976, Honda rolled its all-new prototype open-class road racer onto the Zandvoort starting grid in the Netherlands for a non-championship 600-kilometer endurance race. The bike — actually Honda entered two race bikes at Zandvoort, one each by European distributors Honda France and Honda U.K. — was powered by an engine that eventually would form the basis for the new 1979 CB750K, CB750F and CB900F models. The French team won the Zandvoort race, and later followed that by winning at Mugello, Italy, the opening round for the 1976 Coupe d’Endurance, Europe’s endurance championship series at the time. Long story short, the Hondas won every race on the Coupe d’Endurance calendar that year, including the coveted 24-hour Bol d’Or to easily wrap up the title.

Slippery aerodynamic wind fairings dressed with number plates and Dzus fasteners for quick removal served as perfect aprons to shield from prying eyes the all-new engines that powered those racing laboratories.

Like the engine it was to replace, the new RCB 1000 motor was an air-cooled inline four. The comparison ended there. The new engine, its cases, cylinders and heads painted black to better dissipate heat, spun two — not one — overhead camshafts that monitored the up-and-down movement of four — not two — valves per cylinder. The cylinders were canted forward a few additional degrees, possibly to help centralize mass for snappier, more precise steering input, and the four exhaust headers were routed into a single silencer (racers never use the term muffler!), creating a 4-into-1 system, a design that was becoming ever more popular at the time.

Shortly after debuting the RCB 1000, Honda equipped all team bikes with its patented Comstar wheels that used pressed stainless steel spokes riveted to spun aluminum rims. Those wheels soon found their way onto production-series CB750s, first the SOHC 1977 CB750 Super Sport and later the 1979 F-model twin-cammers.

Various other technology was gleaned from the RCB racers, and by 1980 and one year after the new CB variants had been put to market, Honda conformed its racers to the revamped FIM world championship endurance rules requiring all entries be production-series models. Enter the CB900F-based racer, still known as the RCB 1000.

Having dominated the endurance racing scene from 1976-1979 with prototype bikes, Honda continued winning with its new production-based racer as well, scooping the 1980 championship to confirm yet again that racing can improve the breed. Using racing to accomplish necessary R&D, Honda Motor Co. had again gone full circle, this time with its inline 750 concept. MC

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