Kawasaki ZX-6R, Honda CBR600RR And Yamaha YZF-R6 - Maximum Middleweights

Josh Herrin's Graves Motorsports Supersport Yamaha YZF-R6
With the early introduction of the '08 R6, Graves Motorsports was able to get a head start on developing the bike for AMA Supersport use, and by the time our test rolled around in early December Josh Herrin's '08 racebike was well into development. And according to the Van Nuys-based Graves team, the improvements from the '08 upgrades are just as noticeable in Supersport trim as they are on the stock bike.

Inside the engine, changes are limited by Supersport rules to cam timing, a YEC (Yamaha Engineering Corporation, the company's racing subsidiary) kit head gasket, valve job and higher compression ratio. Externally, however, Yamaha's kit ECU lets the team take advantage of the electronics incorporated into the R6's throttle bodies. In addition to the usual fuel- and ignition-mapping adjustments, the YEC black box allows the rpm at which the variable-length stacks operate to be changed. The addition of YCC-I, with this adjustability, is a big positive, according to team owner Chuck Graves. "You can have power down below and up top. Instead of always working to have it on one side or the other, now we can have long stacks and short stacks." Furthermore the ECU can alter the rate at which the electronically controlled butterflies open, and this can help the rider be smoother with throttle applications. A Power Commander piggybacked on the YEC box allows further fine-tuning of the fueling as well as the addition of a quickshifter.

On the exhaust side the short Graves Motorsports 4-into-2-into-1 system is an off-the-shelf "works" header system, and the team is experimenting with the carbon-fiber canister's length. Other Graves parts include the rearsets, clip-ons, steering-damper mount and engine covers. Although data acquisition is not allowed in the AMA's Supersport class, the team tests with a Magneti Marelli system, which was installed for our test day. "We can monitor what's happening with the wheel speeds, the lambda sensor, suspension travel and what's happening with the rider and the brake pressure-all the things that we want to look at so we can help the rider and the mechanics refine the motorcycle," Graves says.

We couldn't wrangle any overall power numbers out of the team, but we did find out the '08 model in Supersport spec makes 10 horsepower more in the midrange than last year's similarly modified machine and six horsepower more on top. The midrange improvement is in line with our findings on the stock bike, but the team has found some significant advantages in top end compared with last year's model. And though we found this year's R6 to be a few pounds heavier than last year's, the '08 racebike is slightly lighter-the additional weight on the stock bike is evidently all in the exhaust system.

Suspension modifications are likewise limited in the class, and Herrin's R6 sports an Ohlins TTX shock along with Ohlins complete replacement cartridges inside the stock forks. Wheels are stock, shod with Dunlop DOT race tires. "There are usually three or four different compounds and constructions that will be available," Graves says. "Nothing really wild or out of the ordinary, which I think is good. I think on a race weekend if you had too many choices you'd just get yourself in trouble. You just need to pick the right compounds-what suits that rider-and the settings around [them]."

Overall Graves reports that every change made to the '08 R6 is an improvement as far as performance in race trim. "We have better mass centralization; we have a better-balanced chassis, flexwise. The old bike was pretty stiff. This one has got a little bit better balance to it, and that's overall-from the fork tubes and the triple clamps to the frame and the swingarm. The engine makes more power; it has less friction and variable stacks. We got better valve springs this year and a higher-compression piston."

Even after riding the Graves YZF-R6 back to back with the more powerful Formula Xtreme bikes, Kunitsugu raves about the Supersport Yamaha's power, handling and brakes. "Superb power from the engine, with way more midrange than a stock R6 could ever dream of. Transition to the top end was nice, not a harder hit like the Attack Kawasaki. Superstrong on top, obviously not quite as beefy as the two FX bikes, but unbelievably fast for a Supersport-spec 600. Power started to peter out above 15,250 rpm, so it was best to shift there.

"The chassis was its real strong point, however-the same R6 agility it's always been noted for, only amplified on the racebike without being too twitchy or nervous like I was halfway expecting. Front-end feedback was excellent, and I always knew what the front tire was up to. Coupled with the razor-sharp steering I felt like I could put the Graves R6 anywhere I wanted in a turn, unlike the FX bikes that made me fight the big rear tire all the time. That's not to say the FX bikes were ponderous or anything; it's just that compared with the R6 they were a little heavier steering. Traction from the Dunlop NT D209s was excellent. The brakes were probably the best of the lot, even compared to the Brembos on the Attack Kawasaki, but that is really nitpicking. It's more that they were suited to my riding style, with a lot of progression, great feel and monster power."

"He's a fighter," Graves says of Josh Herrin, the team's sole rider in 2007. "If we can give him a motorcycle that's pretty close to the window come race time, he'll make up the difference. Bringing Ben Bostrom into Supersport along with Josh, we have a benchmark to help Josh learn to set up a motorcycle and refine it for what his likes are and a benchmark for where the machine should be. We used Ben a couple of times last year to help us help Josh so that Josh would have a benchmark, and Ben's been super about that. This is exciting for us going into this year."