Rc51

RC51

Big pistons and the latest technology come at a surprisingly low price

STEVE ANDERSON

IF ONE WERE EVER TO GET THE IDEA THAT HONDA'S RC51 is just a slightly hot-rodded VTR1000, Honda quashed that concept with a throw-away line buried deep in its press kit: "Gear-driven camshafts utilize three-axis drive gears to maintain accurate valve timing and durability at sustained engine speeds." That is the only reference to the RC's geared cam drive. They're just details, why should anyone care?

Because it reveals just how different the RC51 is from the VTR, and how seriously Honda has prepared the bike for its Superbike role. Not only will the RC5 l-along with the CBR929RR-be the sportiest motorcycle in Honda’s line, it will also serve as the basis for the company’s U.S. and World Superbike racing efforts. And Honda doesn’t race to lose.

Consequently, the RC is not a VTR with hotter cams. Instead, it’s a thorough re-engineering of the VTR's 90degree V-Twin concept. Start with the engine-Honda did. Castings are new, and almost every detail, down to the bore and stroke, has changed. The VTR measured 98.0 x 66.0mm, right in the 1.5:1 bore/stroke ratio range favored by almost all new Japanese sportbike engines. But the RC pushes that farther, to 100.0 x 63.6mm, eking out an extra few hundred rpm in rev potential with the shorter stroke, and pushing closer to the extreme bore/stroke ratios of modem Formula One automotive engines. Those huge pistons span just .060 of an inch less than those of a small-block Chevy. The cylinders that they mn in are fabricated by Honda’s powder-metal process that combines aluminum, ceramic and graphite for a lightweight liner with high durability, excellent heat transfer and low friction-no heavy iron here. Then, there’s that cam drive, with a stable system of three gears reaching up from the crank to drive gears on the cam ends, and taking the place of the VTR’s less expensive cam chain. It wasn’t that long ago

that geared cam drives were an exotic piece of Honda Sixties’ Grand Prix lore; now the company barely bothers mentioning them. The cylinder heads for the RC are new, with bigger valves and betterbreathing ports. Feeding the inlets are two enormous, 54mm throttle bodies that are part of a racing-caliber injection system. With an operating pressure of 50 psi, and two injectors per cylinder,

the system can squirt deposits of finely atomized fuel at precise times to maximize inlet cooling and improve charge density, while metering fuel accurately over the entire engine operating range-something difficult for singleinjector systems to do, and vital for the best throttle response.

The peripheral systems support the internal engine updates. The airbox has grown from 8 liters on the VTR to 9.4 for the RC, and is now fed ram air through an efficient, centrally mounted duct that flows right through the steering head back to the airbox. Muffler volume has grown similarly, from 9

liters to 10.6; big Twins need big mufflers to make horsepower while passing sound checks.

The results reported by Honda are impressive. The company claims 130 horsepower at the crank, which should translate into about 112 horses or more reaching the rear wheel-making the RC one of the most powerful Twins ever.

More impressive, though, is the shape of the power curve.

Honda’s charts show it dipping ever so slightly and briefly below that of the torquey VTR somewhere around 3500 rpm, matching that of the VTR in the midrange, and then simply taking off at the top. In other words, almost nothing is lost from the strong VTR midrange, while impressive topend is added.

Carrying this newly bulked-up VTwin is an equally new chassis. When Honda came out with the VTR, there was much talk of “con-

trolled rigidity” and how a chassis could be designed “too stiff.” But when development of a racing model started around the VTR, one of the first needs determined was for greater chassis stiffness. On the VTR, the engine cases contained the swingarm pivot, and the main frame was reduced to a bracket that attached steering head to engine. For the RC51, Honda has reinvented the full frame. It reaches down to and around the swingarm pivot, with the pivot bolt now passing through both frame and engine. With substantial amounts of aluminum added, the RC51’s frame-at 25.6 pounds-is fully 8 pounds heavier than that of the VTR. The swingarm itself fills all available space with aluminum structure, just like that of any other Superbike contender. All this helps explain why,

at 432 pounds, the claimed dry weight of the RC is 10 pounds heavier than that of the VTR. The new structure, though, according to Honda, is extremely rigid.

While stiffening the frame,

Honda engineers didn’t forget the suspension. The VTR’s conventional fork is gone, replaced by an upside-down Showa unit.

Both the fork and shock use Honda’s HMAS (Honda Multiple Action Valving) system, which gives fine control of both lowand high-speed compression damping. But the suspension performance goes beyond function:

The components look just like those fitted to HRC machines.

In truth, the Honda Racing Corporation’s reputation is played to the hilt on the RC51; the HRC logo is cast into engine covers, the wheels are six-spoke designs that look like those used on works racers, and yes, the finish and decals of the fork and

shock match those of the Showas used on GP bikes. Even the left headlight is used exclusively for low beam, recalling the asymmetric lights of Suzuka 8-Hour endurance bikes. More importantly, the RC spent at least as much time in the wind tunnel as any GP bike.

According to an American Honda spokesman, the new V-Twin is the second most aerodynamic bike Honda has ever sold, and the slickest Honda ever offered in the U.S. (Only the Japanese-market 400cc V-Four NC30 had less drag.) The low drag results from both a small frontal area, and from details such as the side-mounted radiators that cool more efficiently. Top speed has benefited dramatically, claims the spokesman, with the RC capable of a speed roughly equal to that of the 929, which makes fully 20 more horsepower. If so, expect to see a 170plus-mph production Twin. Who’d have thought it a few years ago?

Not everything is ^totally track-oriented, however. In terms of riding position, the RC is actually quite close to the VTR.

with the seat-to-pcg ^relationship almost identical. Befitting its racer-replica status, though, the handlebars are slightly lower. And breaking from the tradition set by the RC30 and the RC45, the 51 comes with passenger pegs and a rear seat to replace the tailcowl.

Not to worry that the RC is just another street poser, though. The three stages of HRC race kits promise to eliminate that possibility. Fit them all-availability and price yet to be determined-and you’ll have 180 horsepower at the crank, claims Honda.

All in all, the RC51 is the i raciest Honda ever aimed at a large market. For unlike its V-Four predecessors, the 51 carries a popular price tag:

[ S9999. And if this Twin is * anything like what Honda has described, the only tag you’ll see on an RC51 sitting in a dealership is this: SOLD. □