The long rumored Honda MotoGP V-4 inspired RCV 215 Superbike finally broke cover in Prototypeform at EICMA a few months ago. Because this example features both street lighting and straight un-silenced exhaust pipes, and top end Ohlins Superbike Suspension, it is not exactly ready to race or to be sold to the public. We might hope for the production model to follow next year, with homologation for World Superbike in 2016.
Honda’s work with V-4s dates back to the NR500 oval-piston GP project of 1977-81. Prior to that, all Honda GP engines had been inline four-strokes, and championship-winning fours had carried the Honda name to world prominence. Yet engineers were dissatisfied with the inline-4 because it consists of two 180-degree twins set end-to-end. Each such twin wobbles vigorously about its center, applying a bending moment that flexes and may in time crack the crankcase and cause cylinder base-gasket leakage. To better contain this, in 1961, Honda’s racing engineers mastered the difficult task of casting the 250 racer’s upper crankcase half and the complex finned cylinder block in a single self-bracing unit. Such unit-case/cylinder construction was later applied to Honda’s CBR production inline-4s for the same good reasons.
The NR500 was built as a V-4, its crankcase and two cylinder blocks forming a compact, box-like structure that maximally centralized engine mass. If a 90-degree cylinder angle were chosen, the right and left cylinder pairs of such an engine could be self-balancing in the same way as Ducati’s 90-degree V-twins. NR500 failed to win a single GP point but did conceptually father the long line of Interceptor/VFR V-4s, which culminated in the World Superbike-winning RC30 and RC45. It is thought that five of the RC45’s highly sophisticated cylinders were the starting-point of Honda’s first MotoGP engine, the V-5 RC211V.
Although for some time Honda’s V-5 and later V-4 MotoGP engine architecture was compared unfavorably with the inherently more mass-forward inline concept favored by Yamaha (whose M1 has always been an inline-4), Honda has made the V-4 dominant in MotoGP in 2011-14.
