Under the skin: Honda’s factory RC45 – the world Superbike
REINVENTING THE WHEEL
Sir Alan of Cathcart delves deep into the world of the bikes that took the Honda RC30 concept and moved it on by a country mile. Just looking at the servos under the seat, for the linked braking, is sign enough that this bike was just outrageously interesting.
It’s been two decades since the RC45 retired from global competition. It’s worth remembering just how strong a machine the single-sided factory machine was against the other diesels.
Honda knew it had to come up with a radical advance on current four-cylinder Superbike technology if it was to stand a chance of elbowing its way back to the top of the rostrum. It had been a three-year absence from the Superbike paddock – a long time in racing. It was either get the four-cylinder faster, build a better V-twin or get to grips with a superior CBR900RR Fireblade-style in-line four, to defeat Ducati and Kawasaki at their own game. Those options may have been considered, and despite corporate denials perhaps even tested, but in the end there was only ever going to be one choice. The RC45 had to be a 90º dohc V4, like its RC30 predecessor, but with the gear camshaft drive moved from the centre of each bank of cylinders to the right side. This allowed weight and bulk to be reduced, by eliminating one crank journal and one cam journal, narrowing the engine and also reducing internal friction losses. Total included valve angle was reduced from 38º on the RC30, to 26º on the RC45. Combined with the offset camdrive which gave a steeper, straighter shot at the 2mm bigger inlet valves, and the radically different combustion chamber design (still with a single central plug per cylinder), this greatly improved cylinder filling on the shorter-stroke 72 x 46mm engine, which in standard form weighed 4kg less than the RC30 motor measuring 70x 48.6mm, even though the bike as a whole scaled 4kg more in street guise.
How Honda shaved weight
Much of this weight-saving came from technology carried over from the RVF750 Suzuka 8-Hours and Isle of Man TT racer, such as the metal composite (sintered aluminium powder mixed with graphite and ceramics) cylinder sleeves saving 1.4kg which Honda claimed also offered improved heat dissipation and reduced frictional losses. Titanium rods were employed, as on the RC30, plus three-ring slipper pistons (tworing on the works Superbikes, where oil consumption wasn’t such a factor), offering 11.5:1 compression on the standard engine – 13.2:1 on the Superbike. The close-ratio six-speed gearbox used an eight-plate 140mm clutch compared to the RC30’S 10-plate 125mm one, still a sprag-type oil-bath design even on the Superbike racer. The RC45 chassis used two large castaluminium sections for the steering head and swingarm pivot point, with extruded triple-box aluminium spars connecting them. There is no facility for altering the stock 24.5º head angle as on Ducati’s 916, so riders had to juggle with ride heights and offsets for the 43mm Showa race fork (up from 41mm on the roadster) to obtain the steering geometry they wanted. The beefier frame spars held the engine clamped in place via welded-on alloy pressings like those on the RVF. A revised version of Honda’s trademark Elf-derived ProArm single-sided rear swingarm had the usual Pro-link rising-rate link.
Headline 1997: Champion at last
Honda’s V4-engined RC45 had a difficult birth, at a time when Superbikes were challenging 500GP lap records. It took four years for the successor to the legendary RC30 to win the World Superbike championship, but on the eve of Honda’s corporate 50th birthday, American John Kocinski delivered the prize the company’s founder Soichiro Honda coveted above all others. That title was the top honour in four-stroke motorcycle racing for a company whose corporate and sporting success over the
previous half-century had until recently been based on ever more sophisticated fourstrokes. To do this in 1997, the company’s engineers produced a virtual four-stroke GP bike that revved to nearly 15,000rpm. It was a sweet triumph for Honda, whose previous World Superbike titles had been won a decade earlier in 1988/89, courtesy of Fred Merkel and the Team Rumi RC30. Honda then sat out the Superbike class at world level for three years at the start of the decade, while they worked on their next-generation successor to the RC30. But throughout this time they continued to win Suzuka 8-Hours endurance races run to TT Formula 1 rules on the RVF750, which allowed full-on four-stroke racers with essentially just the engine castings derived from a streetbike. The absence from contention as the Superbike class attained significant world status must have been acutely frustrating to Honda management, in commercial as well as sporting terms. Then to make matters worse, the RC45 was at least a year late when it finally appeared at the end of 1993. The new bike had a troubled debut season, although Aaron Slight’s eight second places in 1994 without ever quite achieving a race victory, showed it could be a contender. It suffered handling problems exacerbated in 1995 by a swap from Dunlop to Michelin tyres. Team manager Neil Tuxworth’s Britishbased Castrol Honda team had been charged with World Superbikes victory in 1997. HRC chief engineer Shuhei Nakamoto had supplied a 186bhp version of Honda’s V4 engine. John Kocinski recruited from Ducati in a straight swap with Honda’s Carl Fogarty, was the vital final piece of the puzzle. Eventually it was mission accomplished for the Castrol Honda team, with Kocinski clinching the world championship ahead of Ducati’s Fogarty and his Honda team-mate Aaron Slight. Debuting on racetracks in 1994, the RC45 took time to obtain Honda’s targeted dominance in World Superbike racing. Riding the Castrol Hondas of John Kocinski and
Aaron Slight at Sentul revealed that to do so and win the 1997 World Superbike title, Honda had reinvented the RC45 motor – a fact confirmed by talking to the leader of the R&D team charged with bringing up baby, HRC’S chief engineer Shuhei Nakamoto. “Between the 1996 and 1997 seasons, we made many detail changes to the engine specification,” Nakamoto told me. “On its own, each was maybe quite small – but together, they gave a major improvement in engine performance. Compared to 1996, we had about 10bhp more on this year’s bike, giving more than 180bhp at the gearbox, at our 14,750rpm power peak. This is more powerful than our world champion NSR500 Grand Prix machine!” Indeed, such power figures used to be the exclusive copyright of 500GP two-strokes, and helped explain how the four-stroke Superbikes of the era had so greatly narrowed the performance gap with GP racing, as well as arguably overtaking it in terms of spectacle. The main factor in Honda’s horsepower hike for 1997 was the adoption of twin injectors for the 72 x 46mm 16-valve V4 motor’s PGM-F1 EFI. Combined with larger air intakes and a bigger airbox, as well as revised valve and ignition timing, this delivered a significant power increase from 10,000rpm all the way to the 14,750rpm redline – and maybe beyond. Riders from rival teams reported constantly hearing the Castrol Hondas fluttering the revlimiter for extended periods of time when locked in combat with them, as if the engine wanted to keep pulling stronger but was prevented from doing so by a revlimiter imposed in the interests of reliability.
Which begged the question: did Honda shift the revlimiter to 15,000 revs or more on occasion, for use when needs be? Maybe. Whatever, the twin injectors (already used for some time by Ducati on their big-bore V-twin, but never before on an engine with four smaller cylinders) were used sequentially, as Nakamoto explained: “Before, with a single injector system, we needed much gasoline at maximum revs, but not so much on the bottom side, which compromised performance. For this year, twin injectors not only made development easier, but also improved engine settings all through the power curve. We use the first injector only until 8,000rpm, then the second one comes in as well, to give maximum fuel flow. We can change the point at which this happens, but so far we didn’t do so at races, only in testing. But it made a big improvement to engine performance.” This step largely enabled HRC technicians to fill in the midrange trough in the power curve which on the RC45 had previously necessitated the use of variable-length intake trumpets in the four 46mm Keihin throttle bodies, to provide a solution. Just as well, because fitting the second injector meant there was no longer any space available for the ‘adjustable air funnels’, as they were called in Hrc-speak, which were anyway banned in AMA Superbike racing, in which American Honda’s Ben Bostrom was crowned champion in 1998 using a spin-off version of Kocinski’s 1997 world champion RC45. But part of this improvement also came from Honda’s ability to fine-tune the fuelling for various parts of the power curve via their on-board adjustment system, whereas Ducati could only do this by swapping EPROM chips on their less user-friendly Magneti Marelli EFI package, which did however have the ignition incorporated in it, for a fully-integrated engine management system. Honda used a separate
Nippondenso ignition which, while fully programmable even down to choosing a different curve for each ratio in the six-speed gearbox, was still completely separate from the EFI. Nakamoto revealed why: “The truth is that we have two separate suppliers, one each for injection and ignition – and maybe we would need a third to provide us with an integral system!” he smiled. Still, one area the two packages did meet was on the wide-open powershifter for the gearbox, which in 1997 for the first time also worked by cutting out the ignition (as on other bikes) as well as a the fuel supply, which was all it did before. b But the transmission still didn’t use u a dry clutch, even at the cost of the power p sacrificed by the increased drag of o the wet oil-bath unit used on every works w V4 Honda Superbike ever built. “The problem is that our back-torque limiter [Hrc-speak for a slipper clutch – Ed] would necessitate a very large oil seal if we fitted a dry clutch,” said Nakamoto. “Not only does this create concern about oil leaks, but also oil consumption – and please understand this machine was also developed for success in the Suzuka 8-Hours, as well as other long distance events.” However, one of the many detail improvements for 1997 was adoption of a Ducati-style side oil feed for the crankshaft, to reduce drag – though the design of the titanium rods, two-ring slipper pistons giving 13.2:1 compression, cylinder head porting and cam profiles all remained the same, and while the same sizes as before, the shape of the titanium valves was slightly changed, and springs and retainers were new. Yet that hefty power increase hadn’t been
accompanied by a notable increase in top speed, with trap speeds hardly any higher that year than before. “That’s correct,” said Nakamoto. “While our power increase for this season was a big improvement, straight line speed was not so different, because we calculate we need 5bhp more power for each 1kph more in top speed. The problem is aerodynamics – and of course for Superbike, we cannot change the body shape from the homologated street bike, not like in GP. “So the main benefit of this extra power is in the improved acceleration.” This helped explain why at high speed circuits like Hockenheim or Daytona, where acceleration wasn’t so much a factor as outright top speed, the Honda’s supremacy wasn’t so evident – whereas on tighter tracks like Laguna Seca or Albacete previously thought to favour the more nimble Ducatis, the RC45 was unbeatable thanks to its improved acceleration. Honda’s main development for its championship season went into the motor, and it paid off with the world title, but, by contrast, the RC45’S chassis was very little changed, said Nakamoto, the only major novelty being the introduction of a race version of Honda’s CBS linked-brake system introduced on the CBR1100XX Blackbird street bike a year earlier. Whether this was adopted on the RC45 for marketing or functional reasons was hard to decipher, and of the Castrol Honda team’s two riders, Kocinski didn’t use it on the grounds it did nothing he couldn’t do himself with separate foot and hand controls, while Slight said he liked it because it made the bike more stable under the heavy braking that was all part of his stop-and-go riding style. The Racing CBS linked system on the RC45 worked via an electric servo motor mounted under the chassis crossmember beneath the seat, computer-controlled via a sensor which monitored pressure on the front brake lever. This led the servo to operate two of the four pistons in the rear brake caliper an instant before the front, to encourage a pro-dive mode, resulting a lower cee of gee and more balanced, thus theoretically more effective, braking. But Honda engineers could alter the settings via the dedicated ECU mounted above the servo, working on three parameters: the pressure on the front brake lever, the length of operation, and the time lag between front and rear, adjustable over a 1/10th to 1/100th second range. And of course the rider could still increase rear wheel braking force at will, by using the foot lever to operate the second pair of pistons in the rear caliper, via the secondary, conventional hydraulic system.