Church of MO: 2003 Honda CBR 600 RR – Part One: On Paper

Due to circumstances beyond MO control, ahem, we did not ride the new Honda CBR600RR at last week’s U.S. press launch, but we do have the scoop on what Honda says is “the most advanced sport bike Honda has ever produced.”

No big, really: Like we said after young Sean’s rain-out on the Kawasaki ZX-6R/ RR (see also the recent follow-up ZX-6R track test), we don’t really need to ride this new RR to know it’s going to be a far more capable motorcycle than nearly everybody who buys one. The question as to which of this latest herd of trick 600’s — Yamaha R6, Kawasaki 636R or Honda CBR600RR–is the real performance king is simply too close to call until a real same-day comparison can come together.

And even at that, I feel safe in predicting that the winner will be by a nose (and highly subjective). Press reports we have read in other places, and reliable sources within the U.S. motopress, lead us to believe the new CBR is, as suspected, fault-free and extremely competent. Surprise. I’m not being flip when I say if you want a new 600 in ’03, going for the one you like the looks of, from a dealer you like to deal with, would not be a bad strategy.

On to the CBR-RR then. It’s all-new. As you know, Honda’s strategy with the long-running CBR600 has always been “big-circle” philosospy–one bike able to do it all, from daily driver to Daytona racer. With the RR, that philosophy is history. The superzoot racey RR will be sold alongside the pre-existing CBR600F4i–now relegated to sensible-shoes status. On paper, the two bikes don’t look dissimilar at all: specs say each weighs 370 pounds dry, 54.7-inch wheelbase for the RR vs. 54.5 for the F4, 24-degree rake for both and nearly identical trail figures (95 for RR, 96 for F4). Both bikes even have 67 x 42.5mm, 599cc engines with 12:1 compression.

The difference lies in the packaging: in the RR, the rider and engine have been moved forward, transmission shafts have been stacked a’la Yamaha, and the swingarm’s been lengthened also a’la Yamaha–all of which produces a bike that can banzai deeper into corners thanks to superior front-end traction and feel. Honda’s beating the mass-centralization gong again. The transmission mainshaft now lies 48.4mm above the centerline of the engine cases, which allowed the countershaft to move closer to the crankshaft. Rotating exhaust ports 30 degrees downward (compared to the F4i) moved the headers rearward enough to shove the compacted four-cylinder even further forward. The fuel tank, or most of it anyway, sits where the F4’s rear shock used to be.

Those things allowed Honda to push the rider fully 70mm further forward. Again, just like Yamaha and its new R6, Honda built the RR’s all-new frame using an all-new aluminum casting technique: “Hollow Fine Die-Cast” is not a rapper, it’s the way Honda now lines sand molds with ceramic, which makes possible finer castings with wall thicknesses as thin as 2.5mm. (Yamaha’s new technique involves using vacuum to suck molten alloy into its molds.)

Using this technique in the steering head, main spars and swingarm pivot plates, Honda says, gives its engineers greater latitude in tuning frame rigidity for “enhanced handling.”

Compared to the F4i, the RR has greater torsional stiffness in the steering head, decreased lateral stiffness due to thinner rear frame rails and vertical stiffness “uncompromised by a beefy structure for the top shock mount.” All of that, taken from the RC211V, is said to result in less wheelspin at corner exits.

Mr. Swingarm is all trick too, and controlled, like on the RC211V GP Honda, by Honda’s new “Unit Pro-Link” linkage system, which sort of compresses the shock from the bottom instead of the top, therefore causing compression of the shock to pull on the lowest frame crossmember instead of pushing on the middle of the frame in typical fashion. It sounds cool and looks cool; mostly it makes room for the RR’s 4.8-gallon fuel load to be moved into the much better location the shock used to occupy.

The top half of the fuel tank now resides beneath a plastic cover; ahead of it under the cover sits a new, bigger airbox. And speaking of swingarms, stacking the transmission shafts, etc., allowed the swingarm pivot to move 30mm closer to the crank, which in turn made room for the swingarm to be 43mm longer than the F4i’s unit–which produces numerous benefits: better mass centralization again, forward weight bias, and reduced swingarm angle changes as the rear wheel strokes upward.

“Honda says the conventional injectors’ proximity to the intake valve gives instant throttle response.”

The engine shrunk laterally too. The starter migrated from the left to the right side of the crankshaft, allowing the generator to move 21.5mm inboard. Along with reshaped generator and clutch covers and your undertail exhaust, the RR’s got three degrees more lean angle in both directions sayeth Honda. The engine, as we said, is all new too, and Honda says it looked at a bunch of other bore/stroke ratios before concluding that the preexisting one is ideal.

Peak power comes now at 12,500 instead of 12,000 rpm–with newfound overrev potential (watch the Yam R6 Mamola vids to understand the beneficiality of that round a racetrack) all the way out to 15,000 rpm. RR pistons are therefore 131 grams each instead of 145 g (F4i). Smaller piston-pins are 36 instead of 44 g each. New nutless carburized rods weigh 232 instead of 244 grams apiece. Add it up and you’re looking at 4.8 ounces less reciprocating weight, in an engine Honda says is 0.7 kg lighter than the F4i’s. Intake valves are now one mm bigger, at 27.5, all the valves are closed by dual springs, and a new, “dual-pivot” camchain tensioner keeps out the dread whip, when applying the whip in top cog.

Fuel delivery is another item Honda says came directly from the RC211 GP project: DSFI means Dual Stage Fuel Injection. Four 40mm Denso throttle bodies contain one twelve-hole injector each, which masticate fuel and air  below 5500 rpm. Four more twelve-holers are located in the roof of the new, 15-liter airbox, shower-style, and begin spritzing above 5500 rpm about one-billionth of a second ahead of the lower nozzles, all of it perfectly timed by a new, 32-bit ECU. Honda says the conventional injectors’ proximity to the intake valve gives instant throttle response–while the shower shnozzles’ distance gives time for even more complete atomization, as well as a cooling effect that results in a denser charge, 125 times per second at 15,000 rpm.

And this: “A Dual-Stage Air Induction ram-air system feeds dense, cool air to the airbox, but now via larger inner/outer ducts. Extensive testing in the wind tunnel and on the race track showed the larger ducts resulted in a slight increase in steering effort. To counteract that trait, the outer ducts have holes punched through them, an idea Honda successfully tried years before on its Grand Prix roadracers. As a result, the RR makes high-speed transitions with ease and confidence.” That’s all we have for now. Next step, full-blown comparo?