Honda Rc45
HONDA RC45
'94 PREVIEW
SET FOR A SUPERBIKE COMEBACK?
KEVIN CAMERON
NOTHING IS FOREVER. HONDA’S RC30 V-Four, such a revelation in 1987, winner of two World Superbike titles, has been left behind by the newer designs of other makers. Although a classic design, the RC can no longer win titles in World or AMA Superbike roadracing. This is no position for a company accustomed to leadership.
Obviously, a fresh design is needed. What will it be? Official info is scarce, but hints from insiders and photos of the bike taken when it made demonstration laps during the Suzuka 8-Hour endurance race in July are of value.
Its project code is RC45, and it will be powered by a 90degree V-Four with electronic fuel injection. The new bike is said to have a GP-inspired cassette gearbox, which can be pulled with the engine in the frame, permitting ratio changes in under 30 minutes. That will be a first in Superbike racing. The photos show a super-compact machine with a 16-inch front wheel, inverted fork and a ramp-nosed, GP-style fairing with twin NACA slots force-feeding a ram airbox.
A vague catalog of possibility? We need not stop here, for factory whisperings and long-lens photos are not the only sources of information. We can see the shape of the new RC45 in the problems of the old RC30, which fall into four main areas: 1) weight distribution; 2) chassis stiffness; 3) power characteristics; and 4) serviceability.
Ray Commonwealth Plumb, who builds team riders RC30 Mike Superbikes Smith and for Tom U.S. Kipp, says that unless everything is just right, the current bike “pushes the front and slides the rear,” a clear example of insufficient front weight.
It’s no surprise that the RC30-a six-year-old design-is now out of balance. Tire grip has increased since 1987. Weight distribution must keep pace with this, shifting forward to cope with greater rear grip, which otherwise tends to lift or push the front wheel. But the RC hasn't changed.
Change is more easily talked about than accomplished, especially since the RC’s Vee engine spreads its mass out lengthwise, one cylinder bank pointing ahead, the other behind. To have the RC30’s engine even as far forward as it now is, the radiator must be split in two parts, with the front cambox peeking through, close to the front tire. Further forward movement of the engine will require that it be rotated backward, pulling that front cylinder head up, out of the tire’s way. A 16-inch front tire will help here. It is also said that the engine’s cam drives will be moved to the side. This will push aside the “gear bulge” in the leading cam cover, out of conflict with the front wheel.
Weight distribution is only part of the story. Dale Quarterley (long the nation’s leading Superbike privateer) described what he calls “the number-one deficiency” of the late-model RC30s. “The old bike, on a roll-on it hooked up good, it had good weight transfer. But now, with peaky power, it won’t take it. Off turns, it slides now,” he says.
He is talking about powerband-handling interaction-not weight distribution. As originally designed, the RC had strong bottom power. As the opposition improved, the RC’s powerband had to be reshaped from wide and flat to tall and spiky. The powered-up RC30 Superbike, in Quarteley’s words, “doesn’t go anywhere until 9500 rpm.” An engine that hits hard will slide the rear where a smoother band will let it hook up.
Riders and that and even tuners large alike suspension say the present changes RC often “lacks have feel,” little effect. This is characteristic of a flexible chassis. Effects of suspension changes are obscured by the “noise” of chassis flex. Again, this is no surprise. This is a 1987 motorcycle on 1993 tires. It’s an old story; tires get better, so suspension has to be made stiffer. That increases flex, so the frame must be stiffened. The Superbikes of the other makers have been through several cycles of frame stiffening since the RC’s 1987 intro; a stiffer Honda is long overdue.
More specifically, there is criticism of the single-sided swingarm. This unique design, licensed from ELF, was adopted to speed wheel-changing, but has now become a Honda signature technology. Yet a single-sided swingarm is a special problem, for if it flexes laterally, it “steers” the rear wheel. By contrast, a conventional two-beam swingarm flexes as a parallelogram, tending to keep the rear tire pointed straight.
As the Suzuka photos show, the single-sider remains, undoubtedly beefed-up. Expect the RC45 to match the chassis stiffness of its competition, with larger-section frame beams and more extensive bracing, particularly at the steering head.
Power horsepower characteristics bikes. The are harder a part the of power handling comes on in, highthe more it upsets the chassis. The answer is to provide a powerband as wide as possible. Quarterley again: “You need 4000 rpm to work with.”
Powerband width is determined by pipes, cam timing, port sizes-and carburetion. The RC45’s fuel injection may do wonders for its powerband. Carburetors become “confused” at rpm where exhaust-pipe pressure waves suppress the vacuum that makes carbs work, but injection functions normally. The result is smooth running over a wider range.
All the usual “soup-up” techniques narrow the band; shorter pipes, longer cam timing, bigger ports. Experienced engineers would avoid these traps-if they had a choice. But the RC’s built-in limitations may have tied Honda’s hands. What limitations? For one, the all-gear cam drive. Mike Velasco, who tuned RC30s for Freddie Spencer in ’91 and ’92, says that with the original “three-gear” geardrive, “We got harmonics from the crankshaft through the geartrain that were breaking valve springs.” Indeed, Honda has made frequent changes to the valve drive, suggesting chronic valvecontrol trouble.
How could the RC’s valve drive be a design triumph in 1987, but a limitation in 1993? The trend in engine design is to gain powerband width by using shorter-duration but higher-lift cam profiles. Short duration boosts bottom power because it prevents intake-charge backflow. High lift supplies the airflow for higher revs-which go higher all the time. The result is a relatively smooth, very wide powerband-just what the RC45 will need to deal with its competition. Trouble is, profiles like this are violent, with high peak valve accelerations that rattle all the parts in the cam drive. As more vigorous cam profiles and higher revs put more shock through the drive, its design may no longer be adequate. At one time, gear drive was regarded as the ultimate. Could it be that a modem chain drive, with its rubber dampers and its multitude of internal oil films, actually provides a stabler drive for super rpm than Honda’s present gear drive? It’s an open question.
Martin Adams, manager of Commonwealth Racing, notes another inherent limitation of the RC30: its combustion chambers. He says that while the RC bums best at a ratio little over 12:1, its competition is able to use a full ratio or more higher. Compression boosts bottom power-provided it doesn’t make the chamber so tight that it won’t bum well at higher rpm. To have the benefit of higher compression, the RC45 will require a flatter, more compact combustion chamber. That almost certainly means a narrowed valve angle-down from 32 degrees to more like the 20 degrees of the current Kawasaki.
Combustion and porting are interrelated. As the tuner makes ports and valves bigger-the simplest route to high-rpm power-he also reduces intake velocity at lower revs. This, in turn, generates less in-cylinder turbulence, leading to poor combustion. In Japan, making the valves and ports smaller is a common RC30 mod-because they are used on the factory RVF endurance bike. Kenny Augustine, a top cylinderhead specialist here in the U.S., says of this, “Of course. Provided you can get the flow the engine needs, you use the smallest ports you can.”
Imagine two different cylinder heads, each delivering 100 cubic feet per minute on a flowbench. One head achieves this with highly developed, streamlined ports of small size, the other with bigger but cruder ports. The small-port head will equal the big-port head’s top-end, but will deliver superior acceleration. The extra turbulence produced by higher airflow velocity helps speed combustion at lower rpm.
On all inline Superbikes, cam timing can be changed in under an hour; pull the cam cover, loosen the cam-sprocket bolts, change the timing, retighten and check lobe center. On the RC30, the cams are made in halves and pressed into a central drive gear. Timing can be changed only by whole teeth, or by pressing the cam halves out of the gear and carefully re-indexing them-not a track-side operation. A new side cam drive could correct this. Sometime RC30 tuner George Vincensi remarked that although “on the bench, the engine is a dream to work with, it’s a nightmare once it’s in the frame.” Martin Adams described the RC30 as “densepack,” noting that operations that are routine on other designs take so long on the RC30 that they won’t fit the normal pace of race practice. Even to jet the carbs requires unbolting them from their rack. Cylinder liners are integral with the upper case, so cylinder damage requires new cases. A high price was paid for the RC30’s compactness; like the overpackaged NR500 fourstroke GP bike of 1977-81, it became hard to service. Look for clever engineering to correct this in RC45.
And what about the obvious question? Is there to be a Big Bang four-stroke racer? Can Honda’s close-firing-order concept revolutionize Superbike racing, as it did GP racing last season? Reports are that Honda R&D and the Italian Rumi team have already evaluated a pair-firing RVF engine, but it didn’t work well enough to justify the necessary redesign of clutch and gearbox to accept the more concentrated loads. Yet if it had worked, would they be telling us about it? Wait and see.
In machine sum, expect recognizably a 90-degree like the V-Four present design, but with stronger chassis parts and fuel injection. It will be more accessible for adjustments and service. Expect an engine producing, in Superbike form, 160 crankshaft horsepower at about 14,500 rpm, and mechanically safe to at least 1000 revs higher.
Oh, and one other thing. If the limited-edition street-going RC45 comes here to the U.S., expect a whiff of “technological inflation.” The bike’s price may double-to $30,000.
